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Discussion Starter #1
For my conversion, I'm planning on a Z1K-HV and PFC-20. This gives me
some real options on batteries in the future.

The Z1K-HV gives 72-300V range
The PFC-20 gives 12-360V range

(These are both nominal voltages, right?)

So this combo can handle quite a range of pack voltages. I can have 10
or 12 or 16 12V lead-acids (25 if I add more wheels to carry the
weight). Or I can use 93 of the 3.2V50Ah headway packs that are being
talked about, or some other lithium tech when it becomes affordable
(maybe my 2nd or 3rd pack). Or something in the middle. And I can use
these parts on my next EV once the current frame rusts to its grave.
(This is all speculation. There is a 100% chance my first pack will be
lead.) Even for the lead pack, having some breathing room will be
nice. If I find my range to be 2-3 miles shorter than I'd like, I could
squeeze in "just one more" battery (early enough in the pack's life
cycle to make that not a terrible idea, hopefully), without blowing any
voltage limits.

Thing is, I can't find a DC/DC converter that's equally flexible.

The Iota units at evsource are 108-170V or 208-320V. I assume because
they're just switching power supplies meant for 120 or 240VAC usage.
The ones EVA sells don't seem to go above 144V. I know this is probably
the cheapest electrical component, so maybe I shouldn't worry about it
and buy another one when I change pack voltages in the future. I also
don't know if these are nominal voltages or absolute limits. If they're
absolute limits, then a 168V lead acid pack would not be an option with
the lower voltage Iota unit. The Brusa units look good, but the cost
more than the Zilla. Ouch. Running without a DC converter is an
option, but not a good one. A converter that outputs 14V for 10-14V
input might be a compromise to using the accessory battery on its own,
and keep the lights up bright. (Costs about $150) But now I'm just
rambling.

Is anyone else thinking about what they have to do to switch battery
technology in the future, or are you just expecting to configure future
packs for the same voltage as your lead packs?

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Discussion Starter #3
Mark Eidson wrote:
> I had a problem with my DC-DC dropping out when the pack dropped
> during high current loads......I eventually had to add a separate 12V
> battery for the Zilla and associated controls. me
>
Yes, I plan to use a small accessory battery (small SLA or motorcycle
starting battery or something) with the DC-DC, to handle any
high-current spikes. (Power accessories like windows and such, might
want a power steering pump, etc.) It would help in this case too, I assume.

If the DC-DC cuts off when out of its voltage range (and automatically
cuts back on), maybe that's fine for me. I'm pretty concerned about
touching the high end of the voltage range when coming off a fresh
charge, though. Don't want to smell anything in that case.

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Discussion Starter #5
Is that what Otmar suggested, or did you even bring it up with him?
(That's the first thing I would do.)

This seems crazy. If the zilla is powered by an accessory battery fed
by the DC-DC, it shouldn't matter if the DC-DC cuts off. The result
would be exactly what you have now, unless the DC-DC is lame and
actually sucks current from your accessory battery when it undervolts.

Mark Eidson wrote:
> I tried having the batery tied to the DC-DC but I would still get drop
> outs with the main contactor disconnecting and the Zilla reporting
> errors under heavy acceleration. I once had to restore the default
> settings in the Zilla flash to correct errors caused by the dropouts.
> This is problem is caused when the dropouts occured diring hairball to
> Zilla communication......Now I have a separate battery and charger for
> the 12V supply to the Zilla and hair ball. I still use the DC-DC for
> other 12V loads that are not critical to operation. me
>
>

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Discussion Starter #7
> I can't find a DC/DC converter that's equally flexible.

IOTA units (power supply) don't work very well below 110VDC input. When
loaded, their output voltage drops with decreasing input voltage, but they
handle the "brownout" very well. Roland uses them in series/parallel in
his El Camino.

Ditto for the Zivan NG1-DCDC. It holds up better at low input voltage, but
output voltage still sags.

The Belktronix DC/DC works from 84V to 200V. It will do 250V if you keep a
1A or higher load on it. The manual requires precharging BOTH the input
and output before connecting them, so you may need to use a precharge
circuit if you regularly disconnect the input OR the output. I think a few
listers are using them.

If you have an even number of batteries you could connect a DC/DC to each
half of the pack. A 192V pack would feed two 96V DC/DC units. If their
output voltage drops slightly with load (most do), they should draw
similar amounts of current from each pack half.

You could also use the 10-14V input, 14V output converter with a modified
version of Lee's battery balancer. Divide the traction pack up into 10-14V
groups and take turns feeding the DC/DC with each group to avoid
unbalancing the pack.

As a last resort, use another PFC-20/30/50 to keep your 12V battery
charged. They run 60-250VAC, and SHOULD work with 84-336VDC (check w/
Manzanita to be sure). Not cheap, but rock solid (if a bit noisy with the
dual fans).

-Adrian

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Discussion Starter #9
what is the efficency of dual DC/DC converters?


----- Original Message -----
From: "Adrian DeLeon" <[email protected]>
To: <[email protected]>
Sent: Wednesday, January 09, 2008 8:37 PM
Subject: Re: [EVDL] DC/DC with flexible pack voltage?


>> I can't find a DC/DC converter that's equally flexible.
>
> IOTA units (power supply) don't work very well below 110VDC input. When
> loaded, their output voltage drops with decreasing input voltage, but they
> handle the "brownout" very well. Roland uses them in series/parallel in
> his El Camino.
>
> Ditto for the Zivan NG1-DCDC. It holds up better at low input voltage, but
> output voltage still sags.
>
> The Belktronix DC/DC works from 84V to 200V. It will do 250V if you keep a
> 1A or higher load on it. The manual requires precharging BOTH the input
> and output before connecting them, so you may need to use a precharge
> circuit if you regularly disconnect the input OR the output. I think a few
> listers are using them.
>
> If you have an even number of batteries you could connect a DC/DC to each
> half of the pack. A 192V pack would feed two 96V DC/DC units. If their
> output voltage drops slightly with load (most do), they should draw
> similar amounts of current from each pack half.
>
> You could also use the 10-14V input, 14V output converter with a modified
> version of Lee's battery balancer. Divide the traction pack up into 10-14V
> groups and take turns feeding the DC/DC with each group to avoid
> unbalancing the pack.
>
> As a last resort, use another PFC-20/30/50 to keep your 12V battery
> charged. They run 60-250VAC, and SHOULD work with 84-336VDC (check w/
> Manzanita to be sure). Not cheap, but rock solid (if a bit noisy with the
> dual fans).
>
> -Adrian
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev

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Discussion Starter #10
Adrian DeLeon wrote:
>
> If you have an even number of batteries you could connect a DC/DC to each
> half of the pack. A 192V pack would feed two 96V DC/DC units. If their
> output voltage drops slightly with load (most do), they should draw
> similar amounts of current from each pack half.
>
And wire the DC/DC outputs in parallel? They won't have a cow? It
seems like the voltage sensing/regulation of the two units would fight
each other. Or maybe they can output 6V and be wired in series on the
output end as well. (2 small 6V batts, or center tapped 12V if they
exist.) Or maybe it would work fine. It's a neat idea.
> You could also use the 10-14V input, 14V output converter with a modified
> version of Lee's battery balancer. Divide the traction pack up into 10-14V
> groups and take turns feeding the DC/DC with each group to avoid
> unbalancing the pack.
>
Another neat idea. I've always thought fast switching a large series
pack would be a good replacement for DC/DC conversion, but I suspect it
probably requires more power electronics than a DC/DC converter to begin
with, so there'd be no savings. For low power needs, though, maybe it
would be economical.
> As a last resort, use another PFC-20/30/50 to keep your 12V battery
> charged. They run 60-250VAC, and SHOULD work with 84-336VDC (check w/
> Manzanita to be sure). Not cheap, but rock solid (if a bit noisy with the
> dual fans).
>
That sounds creative. My car will probably already have a PFC for
charging, but reconfiguring it for DC/DC every trip wouldn't be
sustainable. It might be good for an emergency field repair. :)

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Discussion Starter #11
This certainly seems to be a weak spot in EV components. Therefore, I
am developing a DC/DC converter that has an input range of 70 to 500
volts with an output of 14.7 volts from 0 to 140 amps. This is a Hot
Juice Electric project and the progress can be monitored at:
http://www.hotjuiceelectric.com/development.html

I bring this up for feedback.

At this time, a working prototype is in testing. All good so far except
for one problem. There is approximately $1,200 in parts alone. I am
afraid that adding labor and enough profit to maintain sustainability
would push the price out of most peoples range.

The project is now being refined to maintain the current specifications
and reliability while reducing the cost. The progress is encouraging,
but I think it would help if I could get some feedback.

So, I present this question to the list: What would be a reasonable
price for a DC/DC converter (I call it Chassis Power Module) that would
maintain 14.7 volts output from 0 to 140 amps with an input range of 70
to 500 volts?
Check out the website for additional information.

Keep the Juice flowing!

Ken





-----Original Message-----
From: Chuck Homic <[email protected]>
To: Electric Vehicle Discussion List <[email protected]>
Sent: Wed, 9 Jan 2008 10:55 am
Subject: [EVDL] DC/DC with flexible pack voltage?



For my conversion, I'm planning on a Z1K-HV and PFC-20. This gives me
some real options on batteries in the future.

The Z1K-HV gives 72-300V range
The PFC-20 gives 12-360V range

(These are both nominal voltages, right?)

So this combo can handle quite a range of pack voltages. I can have 10
or 12 or 16 12V lead-acids (25 if I add more wheels to carry the
weight). Or I can use 93 of the 3.2V50Ah headway packs that are being
talked about, or some other lithium tech when it becomes affordable
(maybe my 2nd or 3rd pack). Or something in the middle. And I can use
these parts on my next EV once the current frame rusts to its grave.
(This is all speculation. There is a 100% chance my first pack will be
lead.) Even for the lead pack, having some breathing room will be
nice. If I find my range to be 2-3 miles shorter than I'd like, I could
squeeze in "just one more" battery (early enough in the pack's life
cycle to make that not a terrible idea, hopefully), without blowing any
voltage limits.

Thing is, I can't find a DC/DC converter that's equally flexible.

The Iota units at evsource are 108-170V or 208-320V. I assume because
they're just switching power supplies meant for 120 or 240VAC usage.
The ones EVA sells don't seem to go above 144V. I know this is probably
the cheapest electrical component, so maybe I shouldn't worry about it
and buy another one when I change pack voltages in the future. I also
don't know if these are nominal voltages or absolute limits. If they're
absolute limits, then a 168V lead acid pack would not be an option with
the lower voltage Iota unit. The Brusa units look good, but the cost
more than the Zilla. Ouch. Running without a DC converter is an
option, but not a good one. A converter that outputs 14V for 10-14V
input might be a compromise to using the accessory battery on its own,
and keep the lights up bright. (Costs about $150) But now I'm just
rambling.

Is anyone else thinking about what they have to do to switch battery
technology in the future, or are you just expecting to configure future
packs for the same voltage as your lead packs?

_______________________________________________
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Discussion Starter #12
Adrian DeLeon wrote:
>> If you have an even number of batteries you could connect a DC/DC
>> to each half of the pack. A 192V pack would feed two 96V DC/DC
>> units. If their output voltage drops slightly with load (most do),
>> they should draw similar amounts of current from each pack half.

Chuck Homic wrote:
> And wire the DC/DC outputs in parallel? They won't have a cow?

No; almost any DC/DC (or even AC/DC power supply being used as a DC/DC)
will work. The key is that they need to have an adjustable output
voltage, so you can set them to each provide half the load current.

If they aren't adjustable, then you need to add a small series
resistance (or equivalent) to each output. A convenient way to do this
is with an output fuse and/or a series diode. The diode has the
advantage of blocking current from flowing from the battery back into
the supply's output. Most supplies draw current from the battery when
they are not powered.

> Or maybe they can output 6V and be wired in series on the output end
> as well. (2 small 6V batts, or center tapped 12V if they exist.)

You can connect two supplies in series, just like batteries. This forces
them to run at the same output current. If one shuts down, the other one
can't deliver any current either. So, it's better to parallel the
outputs instead. If one quits, the other keeps working and charging your
12v system.

You could use two supplies and two 6v batteries; but this gets to be
complicated for no purpose.

>> You could also use the 10-14V input, 14V output converter with a
>> modified version of Lee's battery balancer. Divide the traction
>> pack up into 10-14V groups and take turns feeding the DC/DC with
>> each group to avoid unbalancing the pack.

> Another neat idea. I've always thought fast switching a large series
> pack would be a good replacement for DC/DC conversion, but I suspect
> it probably requires more power electronics than a DC/DC converter to
> begin with, so there'd be no savings. For low power needs, though,
> maybe it would be economical.

My Balancer has a single DC/DC, powered by the pack as a whole. Its 12v
output then gets switched (by relays; one per battery) to whichever
battery needs charging. The 12v accessory battery can be included in
this list, so it can double as your DC/DC converter.

Adrian DeLeon suggested a related method; you could have N small DC/DC
converters, one per battery. They all have 12-14vdc outputs, which are
all connected together (thru a diode and fuse, as mentioned above) to
your 12v accessory battery. If you arrange it right, these converters
load their respective batteries according to their state of charge; so
the highest-voltage battery delivers the most current. This would give
you a DC/DC converter and a battery balancing system.

>> As a last resort, use another PFC-20/30/50 to keep your 12V battery
>> charged.

> That sounds creative. My car will probably already have a PFC for
> charging, but reconfiguring it for DC/DC every trip wouldn't be
> sustainable. It might be good for an emergency field repair. :)

They aren't isolated.

--
Ring the bells that still can ring
Forget the perfect offering
There is a crack in everything
That's how the light gets in -- Leonard Cohen
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net

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Discussion Starter #13
Lee Hart wrote:
> No; almost any DC/DC (or even AC/DC power supply being used as a DC/DC)
> will work. The key is that they need to have an adjustable output
> voltage, so you can set them to each provide half the load current.
>
I half get you, except why do they have to be adjustable? If they both
have the same output voltage it should be good. Or do you mean to
account for manufacturing tolerances, as in even if they're "supposed"
to output exactly the same voltage, they won't.
> If they aren't adjustable, then you need to add a small series
> resistance (or equivalent) to each output. A convenient way to do this
> is with an output fuse and/or a series diode.
The voltage drop of the diode won't confuse things even more so?
> Adrian DeLeon suggested a related method; you could have N small DC/DC
> converters, one per battery. They all have 12-14vdc outputs, which are
> all connected together (thru a diode and fuse, as mentioned above) to
> your 12v accessory battery. If you arrange it right, these converters
> load their respective batteries according to their state of charge; so
> the highest-voltage battery delivers the most current. This would give
> you a DC/DC converter and a battery balancing system.
>
That is sexy, though how cheap can you get 12 5A DC/DC's. Well, don't
they call 'em voltage regulators in that application? Hmm..., actually
that sounds really cheap. :) :)
>
>> That sounds creative. My car will probably already have a PFC for
>> charging, but reconfiguring it for DC/DC every trip wouldn't be
>> sustainable. It might be good for an emergency field repair. :)
>>
>
> They aren't isolated.
>
>
Oh fudge. I knew that. :) Please nobody try that! :)

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Discussion Starter #14
140 amps is nice, but that is a LOT of headroom. Could you offer a smaller
model for less?

Personally, half that would be fine. The biggest load in my EV is the
blower fan @ 28a. I have never seen any combination of accessories pull
more than 68a peak.

-Phil
----- Original Message -----
From: <[email protected]>
To: <[email protected]>
Sent: Thursday, January 10, 2008 8:20 AM
Subject: Re: [EVDL] DC/DC with flexible pack voltage?


> This certainly seems to be a weak spot in EV components. Therefore, I
> am developing a DC/DC converter that has an input range of 70 to 500
> volts with an output of 14.7 volts from 0 to 140 amps. This is a Hot
> Juice Electric project and the progress can be monitored at:
> http://www.hotjuiceelectric.com/development.html
>
> I bring this up for feedback.
>
> At this time, a working prototype is in testing. All good so far except
> for one problem. There is approximately $1,200 in parts alone. I am
> afraid that adding labor and enough profit to maintain sustainability
> would push the price out of most peoples range.
>
> The project is now being refined to maintain the current specifications
> and reliability while reducing the cost. The progress is encouraging,
> but I think it would help if I could get some feedback.
>
> So, I present this question to the list: What would be a reasonable
> price for a DC/DC converter (I call it Chassis Power Module) that would
> maintain 14.7 volts output from 0 to 140 amps with an input range of 70
> to 500 volts?
> Check out the website for additional information.
>
> Keep the Juice flowing!
>
> Ken
>
>
>
>
>
> -----Original Message-----
> From: Chuck Homic <[email protected]>
> To: Electric Vehicle Discussion List <[email protected]>
> Sent: Wed, 9 Jan 2008 10:55 am
> Subject: [EVDL] DC/DC with flexible pack voltage?
>
>
>
> For my conversion, I'm planning on a Z1K-HV and PFC-20. This gives me
> some real options on batteries in the future.
>
> The Z1K-HV gives 72-300V range
> The PFC-20 gives 12-360V range
>
> (These are both nominal voltages, right?)
>
> So this combo can handle quite a range of pack voltages. I can have 10
> or 12 or 16 12V lead-acids (25 if I add more wheels to carry the
> weight). Or I can use 93 of the 3.2V50Ah headway packs that are being
> talked about, or some other lithium tech when it becomes affordable
> (maybe my 2nd or 3rd pack). Or something in the middle. And I can use
> these parts on my next EV once the current frame rusts to its grave.
> (This is all speculation. There is a 100% chance my first pack will be
> lead.) Even for the lead pack, having some breathing room will be
> nice. If I find my range to be 2-3 miles shorter than I'd like, I could
> squeeze in "just one more" battery (early enough in the pack's life
> cycle to make that not a terrible idea, hopefully), without blowing any
> voltage limits.
>
> Thing is, I can't find a DC/DC converter that's equally flexible.
>
> The Iota units at evsource are 108-170V or 208-320V. I assume because
> they're just switching power supplies meant for 120 or 240VAC usage.
> The ones EVA sells don't seem to go above 144V. I know this is probably
> the cheapest electrical component, so maybe I shouldn't worry about it
> and buy another one when I change pack voltages in the future. I also
> don't know if these are nominal voltages or absolute limits. If they're
> absolute limits, then a 168V lead acid pack would not be an option with
> the lower voltage Iota unit. The Brusa units look good, but the cost
> more than the Zilla. Ouch. Running without a DC converter is an
> option, but not a good one. A converter that outputs 14V for 10-14V
> input might be a compromise to using the accessory battery on its own,
> and keep the lights up bright. (Costs about $150) But now I'm just
> rambling.
>
> Is anyone else thinking about what they have to do to switch battery
> technology in the future, or are you just expecting to configure future
> packs for the same voltage as your lead packs?
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>
>
> ________________________________________________________________________
> More new features than ever. Check out the new AOL Mail ! -
> http://webmail.aol.com
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>

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Discussion Starter #15
Who the heck needs 140 amps? Are you planning on powering a 5th wheel too?

I'm just asking. Seems to me that cutting the power in 1/2 would still be
more than adequate and would reduce costs quite a bit.
Heck, I think most people would be happy with 55 amps... well anyone
without a Wayland Sound System (tm)

> This certainly seems to be a weak spot in EV components. Therefore, I
> am developing a DC/DC converter that has an input range of 70 to 500
> volts with an output of 14.7 volts from 0 to 140 amps. This is a Hot
> Juice Electric project and the progress can be monitored at:
> http://www.hotjuiceelectric.com/development.html
>
> I bring this up for feedback.
>
> At this time, a working prototype is in testing. All good so far except
> for one problem. There is approximately $1,200 in parts alone. I am
> afraid that adding labor and enough profit to maintain sustainability
> would push the price out of most peoples range.
>
> The project is now being refined to maintain the current specifications
> and reliability while reducing the cost. The progress is encouraging,
> but I think it would help if I could get some feedback.
>
> So, I present this question to the list: What would be a reasonable
> price for a DC/DC converter (I call it Chassis Power Module) that would
> maintain 14.7 volts output from 0 to 140 amps with an input range of 70
> to 500 volts?
> Check out the website for additional information.
>
> Keep the Juice flowing!
>
> Ken
>
>
>
>
>
> -----Original Message-----
> From: Chuck Homic <[email protected]>
> To: Electric Vehicle Discussion List <[email protected]>
> Sent: Wed, 9 Jan 2008 10:55 am
> Subject: [EVDL] DC/DC with flexible pack voltage?
>
>
>
> For my conversion, I'm planning on a Z1K-HV and PFC-20. This gives me
> some real options on batteries in the future.
>
> The Z1K-HV gives 72-300V range
> The PFC-20 gives 12-360V range
>
> (These are both nominal voltages, right?)
>
> So this combo can handle quite a range of pack voltages. I can have 10
> or 12 or 16 12V lead-acids (25 if I add more wheels to carry the
> weight). Or I can use 93 of the 3.2V50Ah headway packs that are being
> talked about, or some other lithium tech when it becomes affordable
> (maybe my 2nd or 3rd pack). Or something in the middle. And I can use
> these parts on my next EV once the current frame rusts to its grave.
> (This is all speculation. There is a 100% chance my first pack will be
> lead.) Even for the lead pack, having some breathing room will be
> nice. If I find my range to be 2-3 miles shorter than I'd like, I could
> squeeze in "just one more" battery (early enough in the pack's life
> cycle to make that not a terrible idea, hopefully), without blowing any
> voltage limits.
>
> Thing is, I can't find a DC/DC converter that's equally flexible.
>
> The Iota units at evsource are 108-170V or 208-320V. I assume because
> they're just switching power supplies meant for 120 or 240VAC usage.
> The ones EVA sells don't seem to go above 144V. I know this is probably
> the cheapest electrical component, so maybe I shouldn't worry about it
> and buy another one when I change pack voltages in the future. I also
> don't know if these are nominal voltages or absolute limits. If they're
> absolute limits, then a 168V lead acid pack would not be an option with
> the lower voltage Iota unit. The Brusa units look good, but the cost
> more than the Zilla. Ouch. Running without a DC converter is an
> option, but not a good one. A converter that outputs 14V for 10-14V
> input might be a compromise to using the accessory battery on its own,
> and keep the lights up bright. (Costs about $150) But now I'm just
> rambling.
>
> Is anyone else thinking about what they have to do to switch battery
> technology in the future, or are you just expecting to configure future
> packs for the same voltage as your lead packs?
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>
>
> ________________________________________________________________________
> More new features than ever. Check out the new AOL Mail ! -
> http://webmail.aol.com
>
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>


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If you send email to me, or the EVDL, that has > 4 lines of legalistic
junk at the end; then you are specifically authorizing me to do whatever I
wish with the message. By posting the message you agree that your long
legalistic signature is void.

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Discussion Starter #17
Could this system be reversed to put voltage back into you drive pack one
set of 12vdc batts. at a time from an alternator off the shaft of your
motor, say if you were pulling the ev somewhere or even using a pusher
trailer, or is there a more effecient way of doing this?


----- Original Message -----
From: "Lee Hart" <[email protected]>
To: "Electric Vehicle Discussion List" <[email protected]>
Sent: Thursday, January 10, 2008 11:34 AM
Subject: Re: [EVDL] DC/DC with flexible pack voltage?


> Adrian DeLeon wrote:
>>> If you have an even number of batteries you could connect a DC/DC
>>> to each half of the pack. A 192V pack would feed two 96V DC/DC
>>> units. If their output voltage drops slightly with load (most do),
>>> they should draw similar amounts of current from each pack half.
>
> Chuck Homic wrote:
>> And wire the DC/DC outputs in parallel? They won't have a cow?
>
> No; almost any DC/DC (or even AC/DC power supply being used as a DC/DC)
> will work. The key is that they need to have an adjustable output
> voltage, so you can set them to each provide half the load current.
>
> If they aren't adjustable, then you need to add a small series
> resistance (or equivalent) to each output. A convenient way to do this
> is with an output fuse and/or a series diode. The diode has the
> advantage of blocking current from flowing from the battery back into
> the supply's output. Most supplies draw current from the battery when
> they are not powered.
>
>> Or maybe they can output 6V and be wired in series on the output end
>> as well. (2 small 6V batts, or center tapped 12V if they exist.)
>
> You can connect two supplies in series, just like batteries. This forces
> them to run at the same output current. If one shuts down, the other one
> can't deliver any current either. So, it's better to parallel the
> outputs instead. If one quits, the other keeps working and charging your
> 12v system.
>
> You could use two supplies and two 6v batteries; but this gets to be
> complicated for no purpose.
>
>>> You could also use the 10-14V input, 14V output converter with a
>>> modified version of Lee's battery balancer. Divide the traction
>>> pack up into 10-14V groups and take turns feeding the DC/DC with
>>> each group to avoid unbalancing the pack.
>
>> Another neat idea. I've always thought fast switching a large series
>> pack would be a good replacement for DC/DC conversion, but I suspect
>> it probably requires more power electronics than a DC/DC converter to
>> begin with, so there'd be no savings. For low power needs, though,
>> maybe it would be economical.
>
> My Balancer has a single DC/DC, powered by the pack as a whole. Its 12v
> output then gets switched (by relays; one per battery) to whichever
> battery needs charging. The 12v accessory battery can be included in
> this list, so it can double as your DC/DC converter.
>
> Adrian DeLeon suggested a related method; you could have N small DC/DC
> converters, one per battery. They all have 12-14vdc outputs, which are
> all connected together (thru a diode and fuse, as mentioned above) to
> your 12v accessory battery. If you arrange it right, these converters
> load their respective batteries according to their state of charge; so
> the highest-voltage battery delivers the most current. This would give
> you a DC/DC converter and a battery balancing system.
>
>>> As a last resort, use another PFC-20/30/50 to keep your 12V battery
>>> charged.
>
>> That sounds creative. My car will probably already have a PFC for
>> charging, but reconfiguring it for DC/DC every trip wouldn't be
>> sustainable. It might be good for an emergency field repair. :)
>
> They aren't isolated.
>
> --
> Ring the bells that still can ring
> Forget the perfect offering
> There is a crack in everything
> That's how the light gets in -- Leonard Cohen
> --
> Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net
>
> _______________________________________________
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Discussion Starter #18
Josh Creel wrote:
> Could this system be reversed to put voltage back into you drive pack one
> set of 12vdc batts. at a time from an alternator off the shaft of your
> motor, say if you were pulling the ev somewhere or even using a pusher
> trailer, or is there a more effecient way of doing this?
>
I assume a generator that's actually wired for pack voltage would be
much more efficient and cheaper. But this would be such a rare use
case, I wouldn't imagine it being useful at all. This would kind of be
like regen braking without a controller (and thus not very controllable).

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Discussion Starter #19
The expense is in the input range. The current capability adds some
expense, but is dwarfed by the cost of tracking that large of input
voltage range. I chose 140 amps because many OEM cars come with 90 to
140 amp alternators. My personal conversion project, a Pontiac Fiero
has a 140 amp alternator, so I want to maintain that capability and
reliability.
Many EVs use an aux battery to fill in for generally poor DC/DC convert
reliability. I would like to provide a system with enough headroom,
both on the input side as well as the output side to be at least OEM
automotive standard reliable.
Certainly, a DC/DC converter could be designed with less current
capability, but the cost reduction would not be linear.

So, ignoring the output current, what do you think would be a workable
price for a 70 to 500 volt input, OEM automotive reliability DC/DC
converter would be?

Ken




-----Original Message-----
From: (-Phil-) <[email protected]>
To: Electric Vehicle Discussion List <[email protected]>
Sent: Thu, 10 Jan 2008 10:53 am
Subject: Re: [EVDL] DC/DC with flexible pack voltage?



140 amps is nice, but that is a LOT of headroom. Could you offer a
smaller
model for less?

Personally, half that would be fine. The biggest load in my EV is the
blower fan @ 28a. I have never seen any combination of accessories pull
more than 68a peak.

-Phil
----- Original Message -----
From: <[email protected]>
To: <[email protected]>
Sent: Thursday, January 10, 2008 8:20 AM
Subject: Re: [EVDL] DC/DC with flexible pack voltage?


> This certainly seems to be a weak spot in EV components. Therefore, I
> am developing a DC/DC converter that has an input range of 70 to 500
> volts with an output of 14.7 volts from 0 to 140 amps. This is a Hot
> Juice Electric project and the progress can be monitored at:
> http://www.hotjuiceelectric.com/development.html
>
> I bring this up for feedback.
>
> At this time, a working prototype is in testing. All good so far
except
> for one problem. There is approximately $1,200 in parts alone. I am
> afraid that adding labor and enough profit to maintain sustainability
> would push the price out of most peoples range.
>
> The project is now being refined to maintain the current
specifications
> and reliability while reducing the cost. The progress is encouraging,
> but I think it would help if I could get some feedback.
>
> So, I present this question to the list: What would be a reasonable
> price for a DC/DC converter (I call it Chassis Power Module) that
would
> maintain 14.7 volts output from 0 to 140 amps with an input range of
70
> to 500 volts?
> Check out the website for additional information.
>
> Keep the Juice flowing!
>
> Ken
>
>
>
>
>
> -----Original Message-----
> From: Chuck Homic <[email protected]>
> To: Electric Vehicle Discussion List <[email protected]>
> Sent: Wed, 9 Jan 2008 10:55 am
> Subject: [EVDL] DC/DC with flexible pack voltage?
>
>
>
> For my conversion, I'm planning on a Z1K-HV and PFC-20. This gives me
> some real options on batteries in the future.
>
> The Z1K-HV gives 72-300V range
> The PFC-20 gives 12-360V range
>
> (These are both nominal voltages, right?)
>
> So this combo can handle quite a range of pack voltages. I can have 10
> or 12 or 16 12V lead-acids (25 if I add more wheels to carry the
> weight). Or I can use 93 of the 3.2V50Ah headway packs that are being
> talked about, or some other lithium tech when it becomes affordable
> (maybe my 2nd or 3rd pack). Or something in the middle. And I can use
> these parts on my next EV once the current frame rusts to its grave.
> (This is all speculation. There is a 100% chance my first pack will be
> lead.) Even for the lead pack, having some breathing room will be
> nice. If I find my range to be 2-3 miles shorter than I'd like, I
could
> squeeze in "just one more" battery (early enough in the pack's life
> cycle to make that not a terrible idea, hopefully), without blowing
any
> voltage limits.
>
> Thing is, I can't find a DC/DC converter that's equally flexible.
>
> The Iota units at evsource are 108-170V or 208-320V. I assume because
> they're just switching power supplies meant for 120 or 240VAC usage.
> The ones EVA sells don't seem to go above 144V. I know this is
probably
> the cheapest electrical component, so maybe I shouldn't worry about it
> and buy another one when I change pack voltages in the future. I also
> don't know if these are nominal voltages or absolute limits. If
they're
> absolute limits, then a 168V lead acid pack would not be an option
with
> the lower voltage Iota unit. The Brusa units look good, but the cost
> more than the Zilla. Ouch. Running without a DC converter is an
> option, but not a good one. A converter that outputs 14V for 10-14V
> input might be a compromise to using the accessory battery on its own,
> and keep the lights up bright. (Costs about $150) But now I'm just
> rambling.
>
> Is anyone else thinking about what they have to do to switch battery
> technology in the future, or are you just expecting to configure
future
> packs for the same voltage as your lead packs?
>
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Discussion Starter #20
Actually I was thinking of a single DC/DC powered by each traction battery
in turn. Switch input batteries every few seconds to share the load. It
would have wiring similar to your battery balancer. Your interpretation of
my idea is also interesting as it balances the traction pack, but only on
discharge.

> Adrian DeLeon suggested a related method; you could have N small DC/DC
> converters, one per battery. They all have 12-14vdc outputs, which are
> all connected together (thru a diode and fuse, as mentioned above) to
> your 12v accessory battery. If you arrange it right, these converters
> load their respective batteries according to their state of charge; so
> the highest-voltage battery delivers the most current. This would give
> you a DC/DC converter and a battery balancing system.


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