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[EVDL] E-moto: 48V or 72V?

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EVDL,

We are designing a light commuter e-moto with a little over three kWh on board using 16 Ah Headway cells. My question is whether to configure the bike as a 48V system (16S4P) or 72V (24S3P). Each option has some obvious advantages - 48V: slightly cheaper controller and BMS; 72V: smaller gage wiring. Our bike has a chain drive so we can adjust the sprocket sizing to accommodate the max speed of the motor at the different voltages.

Am I missing something obvious in working through this decision? I apologize if this is a stupid noob question, but I've been getting different opinions on the issue from friends and colleagues I've polled.

Thanks in advance for any help!

Tom McKinnon

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Discussion Starter · #2 ·
The incremental cost increase of going to 72 volts is well worth the flexibility the higher voltage gives you. You don't mention any of your design goals, so I will assume you want to be able to go just as far and as fast as possible within your budget :) My experience has been that 72 volts will make those goals easier, and give you more options for tweaking things after the fact.

damon

> From: [email protected]
> Date: Tue, 31 Aug 2010 17:41:35 -0600
> To: [email protected]
> Subject: [EVDL] E-moto: 48V or 72V?
>
> EVDL,
>
> We are designing a light commuter e-moto with a little over three kWh on board using 16 Ah Headway cells. My question is whether to configure the bike as a 48V system (16S4P) or 72V (24S3P). Each option has some obvious advantages - 48V: slightly cheaper controller and BMS; 72V: smaller gage wiring. Our bike has a chain drive so we can adjust the sprocket sizing to accommodate the max speed of the motor at the different voltages.
>
> Am I missing something obvious in working through this decision? I apologize if this is a stupid noob question, but I've been getting different opinions on the issue from friends and colleagues I've polled.
>
> Thanks in advance for any help!
>
> Tom McKinnon
>
> _______________________________________________
> | REPLYING: address your message to [email protected] only.
> | Multiple-address or CCed messages may be rejected.
> | UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
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Discussion Starter · #3 ·
Overall losses at higher voltages are lower as well.

As the current is directly proportional the inverse of the voltage but POWER
is proportional to the SQUARE of the current. This means everything runs
cooler at higher voltages for the same power output from the motor...

Bob Sisson
1993 Geo Metro Convertible Project
Gaithersburg MD


-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf
Of damon henry
Sent: Wednesday, September 01, 2010 10:20 AM
To: EV List
Subject: Re: [EVDL] E-moto: 48V or 72V?


The incremental cost increase of going to 72 volts is well worth the
flexibility the higher voltage gives you. You don't mention any of your
design goals, so I will assume you want to be able to go just as far and as
fast as possible within your budget :) My experience has been that 72 volts
will make those goals easier, and give you more options for tweaking things
after the fact.

damon

> From: [email protected]
> Date: Tue, 31 Aug 2010 17:41:35 -0600
> To: [email protected]
> Subject: [EVDL] E-moto: 48V or 72V?
>
> EVDL,
>
> We are designing a light commuter e-moto with a little over three kWh on
board using 16 Ah Headway cells. My question is whether to configure the
bike as a 48V system (16S4P) or 72V (24S3P). Each option has some obvious
advantages - 48V: slightly cheaper controller and BMS; 72V: smaller gage
wiring. Our bike has a chain drive so we can adjust the sprocket sizing to
accommodate the max speed of the motor at the different voltages.
>
> Am I missing something obvious in working through this decision? I
apologize if this is a stupid noob question, but I've been getting different
opinions on the issue from friends and colleagues I've polled.
>
> Thanks in advance for any help!
>
> Tom McKinnon
>
> _______________________________________________
> | REPLYING: address your message to [email protected] only.
> | Multiple-address or CCed messages may be rejected.
> | UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub
> | OTHER HELP: http://evdl.org/help/
> | OPTIONS: http://lists.sjsu.edu/mailman/listinfo/ev

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72,624 Posts
Discussion Starter · #4 ·
I violently agree with Lee Hart!

HOWEVER...most of us are not building perfectly matched components
purposefully built for a project... we are pulling "stock" components off
the shelf and using them as best we can...

Case in Point... A Warp Motor... what voltage is a Warp motor? Well people
are running them on everything from 48v-144v... Given a choice I would
rather run 144V than 48V...much lower currents and thus losses, but many
more connections and the issues of higher voltages...

The other issue is that "standard" components are often -NOT- rated for high
voltage DC...120VAC is NOT the same as 120VDC, and 144V is even more not the
same...

As lee Hart says, if you can pick all matching purposeful components it
won't make much difference, however, if building from mix-n-match as most of
us do...I would go with the highest voltage you feel you can deal with...

Bob Sisson
1993 Geo Metro Convertible Project
Gaithersburg MD


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