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Discussion Starter #1
I haven't been following this thread from the beginning but I saw the
comment about max draw from 12, and 6v batteries (500 amps on a 12v will
kill it quick)

I'm running 8v floodeds and a Curtis 1221B controller. I've never managed to
hit 400 amps draw. I've hit 300 for a few seconds a few times but when I
hill-climb, sometimes I pull 200-240 amps for as long as 1-4 minutes.

Is this too much for 8v batteries? I have 3,000 miles on them so far and
haven't noticed any problems. Well....'cept for that one that blew up
recently and that was my fault. A loose cable seemed to be the culprit. :(

Rich

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Discussion Starter #2
Re: [EVDL] EV HP

Hello Richard,

This depends where your amp meter shunt is place in the circuit. If its
install between the main battery and controller, you are reading battery
ampere. If it place between the controller and motor, then its motor
amperes.

Motor ampere may be much higher than the battery ampere in some controllers.
I have both meters in my EV, and my motor ampere will read about 110 amps
while the battery ampere is about 50 amps at about 30 mph. At 50 miles per
hour the motor ampere is about 250 amps while the battery amps is at 180
amps.

I find it is more important to monitor the motor ampere which is a large
meter next to the tachometer. Check the normal running ampere of the motor.
My motor is spec for 199 amps continuous, so I tried to keep the motor
ampere at 200 amps or lower.

Roland




----- Original Message -----
From: "Richard Acuti" <[email protected]>
To: <[email protected]>
Sent: Tuesday, August 14, 2007 5:20 AM
Subject: [EVDL] EV HP


> I haven't been following this thread from the beginning but I saw the
> comment about max draw from 12, and 6v batteries (500 amps on a 12v will
> kill it quick)
>
> I'm running 8v floodeds and a Curtis 1221B controller. I've never managed
> to
> hit 400 amps draw. I've hit 300 for a few seconds a few times but when I
> hill-climb, sometimes I pull 200-240 amps for as long as 1-4 minutes.
>
> Is this too much for 8v batteries? I have 3,000 miles on them so far and
> haven't noticed any problems. Well....'cept for that one that blew up
> recently and that was my fault. A loose cable seemed to be the culprit. :(
>
> Rich
>
> _________________________________________________________________
> More photos, more messages, more storage-get 2GB with Windows Live
> Hotmail.
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> http://lists.sjsu.edu/mailman/listinfo/ev

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Discussion Starter #3
Re: [EVDL] EV HP

Ooooh..good point Roland. I should have mentioned that.

My shut is 'tween the pack and the controller. But now you've given me the
great idea to get another one to measure motor amps.

I have the ADC L91-4003 which is rated for 130 amps continuous, 150 amps for
1 hour, 500 amps peak.

I think my particular application rides this motor hard, but within it's
limits. I'm at 128 volts. When I'm on flat road, I draw 80-100 (battery)
amps at 55 mph, 120-140 (battery amps) at 65 mph. When I hill-climb, I pull
200-240 amps for 1-4 minutes at the longest.

When I build the next E-Beetle, I guess I should really step it up to an 8"
ADC huh?

Rich

>Message: 15
>Date: Tue, 14 Aug 2007 06:38:46 -0600
>From: "Roland Wiench" <[email protected]>
>Subject: Re: [EVDL] EV HP
>To: "Electric Vehicle Discussion List" <[email protected]>
>Message-ID: <[email protected]>
>Content-Type: text/plain; charset="iso-8859-1"

Hello Richard,

This depends where your amp meter shunt is place in the circuit. If its
install between the main battery and controller, you are reading battery
ampere. If it place between the controller and motor, then its motor
amperes.

Motor ampere may be much higher than the battery ampere in some controllers.
I have both meters in my EV, and my motor ampere will read about 110 amps
while the battery ampere is about 50 amps at about 30 mph. At 50 miles per
hour the motor ampere is about 250 amps while the battery amps is at 180
amps.

I find it is more important to monitor the motor ampere which is a large
meter next to the tachometer. Check the normal running ampere of the motor.
My motor is spec for 199 amps continuous, so I tried to keep the motor
ampere at 200 amps or lower.

Roland

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Discussion Starter #4
Re: [EVDL] EV HP

Richard Acuti wrote:
> I saw the comment about max draw from 12, and 6v batteries (500 amps
> on a 12v will kill it quick)... I'm running 8v floodeds and a Curtis
> 1221B controller. I've never managed to hit 400 amps draw. I've hit
> 300 for a few seconds a few times but when I hill-climb, sometimes
> I pull 200-240 amps for as long as 1-4 minutes. Is this too much for
> 8v batteries?

There is no current above which life suddenly falls. Instead, the
situation is that battery life shortens as average current increases.

I'd use this for a rule of thumb for flooded or gel lead-acid batteries:

1. Keep the *average* current below the 20-hour amphour capacity.
For example:
- 220 amps for a 6v 220 amphour golf cart battery
- 175 amps for an 8v 175 amphour golf cart battery
- 100 amps for a 12v 100ah deep-cycle battery

2. Keep the *peak* current times the seconds you draw it below
5 times the battery's 20-hour amphour capacity. For example:
- for a 6v 220ah golf cart battery:
220 amps for 5 seconds
440 amps for 2.5 seconds
880 amps for 1.25 seconds
- for an 8v 175ah golf cart battery:
175 amps for 5 seconds
350 amps for 2.5 seconds
700 amps for 1.25 seconds
- for a 12v 100ah golf cart battery:
100 amps for 5 seconds
200 amps for 2.5 seconds
400 amps for 1.25 seconds

If you exceed these rates, you are accepting a shorter battery life as a
consequence. How much shorter depends on how much you exceed these limits.

For AGMs, you can push these limits harder. Depending on the type,
anywhere from 2 to 5 times harder. In part this is because of their
lower internal resistance. But it is also because their basic life
expectancy is perhaps half as much, so you can do more "damage" from
high currents before it becomes the dominant factor in their life.
--
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 #5
Re: [EVDL] EV HP

Just a sanity check here. How could motor current exceed the battery
current? Since everything comes from the battery!

My rash assumption is that the PWM of the controller is causing a falsely
high motor current reading. Any other opinions?
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Discussion Starter #6
Re: [EVDL] EV HP

Wow. Thanks Lee.

In block #2, when I exceed 175 amps, I definitely exceed it for longer than
that. Luckily I don't have to draw more than 175 amps too often. On the way
home today I tried to time how long the periods are than I draw 200 amps or
more. It's kind of hard without an assistant but I think I was
overestimating when I said 1-4 minutes. It's more like 1-2. Less if I'm
driving faster and use my momentum to hop over some of these hills. The
trade off is that I draw more "averaged" amps.: Instead of 80-100 @ 55 mph,
I'm doing 65 mph and pulling 120-160 amps

Based on how hard I hammer my pack, I pulled the arbitrary number of a
10,000 mile life cycle out of my butt for these batteries when I first
bought them. I'm at 3,000 now. It'll be interesting to see what happens.

I get 65-70 mph now with a 128v pack. If I switch to 6v batts at 96v total,
I wonder how much top speed I'll lose.

Rich A.


>Message: 23
>Date: Tue, 14 Aug 2007 12:19:27 -0500
>From: Lee Hart <[email protected]>
>Subject: Re: [EVDL] EV HP
>To: Electric Vehicle Discussion List <[email protected]>
>Message-ID: <[email protected]>
>Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Richard Acuti wrote:
>I saw the comment about max draw from 12, and 6v batteries (500 amps
>on a 12v will kill it quick)... I'm running 8v floodeds and a Curtis
>1221B controller. I've never managed to hit 400 amps draw. I've hit
>300 for a few seconds a few times but when I hill-climb, sometimes
>I pull 200-240 amps for as long as 1-4 minutes. Is this too much for
>8v batteries?

There is no current above which life suddenly falls. Instead, the
situation is that battery life shortens as average current increases.

I'd use this for a rule of thumb for flooded or gel lead-acid batteries:

1. Keep the *average* current below the 20-hour amphour capacity.
For example:
- 220 amps for a 6v 220 amphour golf cart battery
- 175 amps for an 8v 175 amphour golf cart battery
- 100 amps for a 12v 100ah deep-cycle battery

2. Keep the *peak* current times the seconds you draw it below
5 times the battery's 20-hour amphour capacity. For example:
- for a 6v 220ah golf cart battery:
220 amps for 5 seconds
440 amps for 2.5 seconds
880 amps for 1.25 seconds
- for an 8v 175ah golf cart battery:
175 amps for 5 seconds
350 amps for 2.5 seconds
700 amps for 1.25 seconds
- for a 12v 100ah golf cart battery:
100 amps for 5 seconds
200 amps for 2.5 seconds
400 amps for 1.25 seconds

If you exceed these rates, you are accepting a shorter battery life as a
consequence. How much shorter depends on how much you exceed these limits.

For AGMs, you can push these limits harder. Depending on the type,
anywhere from 2 to 5 times harder. In part this is because of their
lower internal resistance. But it is also because their basic life
expectancy is perhaps half as much, so you can do more "damage" from
high currents before it becomes the dominant factor in their life.
--
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 #7
Re: [EVDL] EV HP

Nothing false about it. Think of it this way, watts into the controller is
roughly equal to watts out, and watts = volts x amps. The controller does
PWM because, at least at lower RPM, if you put full battery volts to the
motor you'd exceed current ratings, so the controller does PWM to cut the
RMS voltage to something below battery volts to reduce current and power.

Now since power is about equal on both sides of the controller, and voltage
is the full battery voltage on the battery side, but less on the motor side
due to the PWM, then current has to be less on the battery side for volt x
amps to be the same on both sides.

Thank heavens, or we'd all be toasting our batteries.

Think of the controller as an impedence matcher, or a DC transformer with a
variable turns ratio (if there was such a thing), and it starts to make
sense. It's all about watts.

----- Original Message -----
From: "Tom Jones" <[email protected]>
To: "Electric Vehicle Discussion List" <[email protected]>
Sent: Tuesday, August 14, 2007 2:21 PM
Subject: Re: [EVDL] EV HP


> Just a sanity check here. How could motor current exceed the battery
> current? Since everything comes from the battery!
>
> My rash assumption is that the PWM of the controller is causing a falsely
> high motor current reading. Any other opinions?
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>
>


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Discussion Starter #9
Re: [EVDL] EV HP

Interesting. Here is my understanding of how a typical DC motor controller
works: They use pulse width modulation (PWM)) to control the power applied
to the motor. They do this my switching the traction battery voltage on and
off, varying the percent of time it is on. This is the duty cycle at any
specific throttle setting. So, the voltage is always the full pack voltage,
disregarding small losses. What the motor sees is full pack voltage in
pulses.

Since the voltage in and out is the almost the same, the currents should
also be close. Now, I don't have any real world, hands on, knowledge of
these measurements. So, if anyone more knowledgeable wants to set me
straight, please do. From a simple electrical point of view, if the voltage
is the same you can't create more current. There is no amplification effect.
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Discussion Starter #10
Re: [EVDL] EV HP

Tom,
Check this out,
http://www.4qdtec.com/pwm-01.html
It's no 'amplification effect.'
It shows where the voltage and current is going.
Hope this helps,
Rod
--- Tom Jones <[email protected]> wrote:

> Interesting. Here is my understanding of how a
> typical DC motor controller
> works: They use pulse width modulation (PWM)) to
> control the power applied
> to the motor. They do this my switching the traction
> battery voltage on and
> off, varying the percent of time it is on. This is
> the duty cycle at any
> specific throttle setting. So, the voltage is always
> the full pack voltage,
> disregarding small losses. What the motor sees is
> full pack voltage in
> pulses.
>
> Since the voltage in and out is the almost the same,
> the currents should
> also be close. Now, I don't have any real world,
> hands on, knowledge of
> these measurements. So, if anyone more knowledgeable
> wants to set me
> straight, please do. From a simple electrical point
> of view, if the voltage
> is the same you can't create more current. There is
> no amplification effect.
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>

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Discussion Starter #12
Re: [EVDL] EV HP

Thank you all for enlightening me. I am guessing here that this also has
something to do with using series wound motors. Boy, time goes by. The last
time I had a class in motors was 1971.
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Discussion Starter #13
Re: [EVDL] EV HP

If all the motor controller had was the switch (MOSFET or IGBT) then this
would be true. However, the controller includes a couple other major
components, Freewheeling diodes and input capacitors.

The freewheeling diodes keep the current flowing in the motor even when
the switch is off. The diodes charge up (from the battery) during the
time the switch is off and discharge during the time it's on.
Because of the capacitors, the current going through the switch can be
higher than the battery current, the freewheeling diodes keep this current
flowing during the off time.

The acutal explanation is a bit longer than this and you have to
understand how the inductance of the motor effects the curent and voltage.

The whole combination -inductance, switch, capactor, diode- forms what's
commonly know known as a DC-to-DC buck converter.

> Interesting. Here is my understanding of how a typical DC motor controller
> works: They use pulse width modulation (PWM)) to control the power applied
> to the motor. They do this my switching the traction battery voltage on
> and
> off, varying the percent of time it is on. This is the duty cycle at any
> specific throttle setting. So, the voltage is always the full pack
> voltage,
> disregarding small losses. What the motor sees is full pack voltage in
> pulses.
>
> Since the voltage in and out is the almost the same, the currents should
> also be close. Now, I don't have any real world, hands on, knowledge of
> these measurements. So, if anyone more knowledgeable wants to set me
> straight, please do. From a simple electrical point of view, if the
> voltage
> is the same you can't create more current. There is no amplification
> effect.
> _______________________________________________
> For subscription options, see
> http://lists.sjsu.edu/mailman/listinfo/ev
>


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