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Discussion Starter #1
Hi all,

I have a Currie electric scooter that I commute on around my town. Recently I've become dissatisfied with it's speed, so I have upgraded it from 24 to 48 volts using a 36-48v controller, the stock 24v rated motor, and four SLA 12V 10Ah batteries. The batteries are somewhat generic PowerSonic PSH high-rate-discharge batteries. The scooter is a blast now! GPS shows 25mph top speed on stock gearing! (previously 13 mph before upgrades)

So anyhow, upon upgrading the batteries, I see a much greater voltage sag when in use. For example, after a few miles of riding my voltmeter reads 47v sitting still, but when I take off it will drop to as low as 35! That's at about 3/4 throttle. And as such, the low voltage protection on the controller kicks in and the scooter shuts down.

I'd like some feedback on this if you don't mind? I am wondering if this might be a common EV problem when increasing voltage w/o increasing aH or battery discharge capabilities? For example, if I added another 4 12v batteries in parallel, keeping the same 48V, would that increase the available amperage thus at a given wattage requirement decrease the volts needed?

Secondly, do I risk damage to the system if I override the safety cutoff of the controller and look for a stationary DOD of 70-80% and ignore (within reason) the instant voltage drops while taking off or climbing a hill?

Thanks so much for any feedback you can provide!

Peter
 

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Hi Peter!

Sounds like you're doing something similar to my "Re-conversion of a Scooter" that I recently posted about in the Scooters/Bikes section.

I assume your controller is a 30A? If so, that comes out to around 1440W, or about 1000 more than the motor is really made for.

That's going to add up to some heat, and heat increases resistance.

Also, since the diameter of that motor is probably considerably less than a motor sized for that kind of power, it probably needs even more amps to generate the same torque as a larger motor.

Since your voltage is sagging so much, I'd have to think that you're either burning a lot of extra power as heat somewhere in the system, or you're asking too much from your batteries.

As to your question about adding more batteries- YES... if you double up the batteries and run them in pairs, each battery in the pair only has to supply half the demand of the whole. The more current you pull per brick, the lower the volts will drop across the terminals.
 

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Discussion Starter #3
TX,

Thanks a bunch for the response, it is most helpful!

Nice scooter conversion you have going there. I'll post pics of mine as well soon. Have you checked out the visforvoltage.org forum? There is a subsection for scooters there as well and many have some small scooters that really move.

Yep, it's a 30A controller on a 350W motor :-/. I think I'll upgrade the motor next and possible step down from 48 volts, 10ah, 4 batteries, to 36 volts 20ah, 6 batteries. I imagine the performance will be close to the same due to more consistent power delivery.

Good thoughts, thanks again!
 

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i'd watch the motor temp closely. Maybe mount a temp sensor on the motor with a digital readout mounted on the dash/handlebars. On winter days, probably no problemo. But on summer days Eee-ouch! hot hot hot.
Operating the motor at twice the voltage and maybe twice the current will
reduce the lifespan of the motor. But, i'm sure U are having fun doing it!! :cool:
 

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Discussion Starter #5
I upgraded to a 1000W motor and 48V controller this evening and the results are great!

Speed decreased unfortunately, but that is because this motor is "rated" at 36V versus the other one that was "rated" at 24, so I'm not (yet) doubling the rated voltage on the new motor. However, it has a bigger drive gear so the net lost was only 2 mph (25 vs 23). (FYI, 11 tooth vs 15 with a 90 tooth final gear, chain drive)

However, the torque is wonderful! I can pull a steady 18.8mph up a notable hill right beside my townhome.


So all that being said, I want to understand this system a little more. Could someone help me with some calculations please?

Right now I am using Powersonic PSH-12100FR batteries, spec sheet found here.

I am running 48 volts and the controller is 25 amp. How do I determine what my max draw would be versus what the batteries are capable of? I know that 48vx25a=1200 watts, but how do I determine if my batteries can supply that much drain?

Thanks a bunch for any help!!!

Best,
Peter
 

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Peter,

The max discharge current of those batteries is about 3C, or 31.5A for up to 7 minutes. The max short-burst is 10C, or 105A for 10 seconds.

That's the beauty of the powersonic high-rate batteries.

Keep in mind that the harder you discharge, the more Peukert will chew up your range.

It sounds as if you've bought the same motor I'm using in my scooter, the Currie 1000w 36v, rated at 2600 rpm. Mine has the 15T freewheel sprocket on the motor. This motor should be plenty torquey, like you say, but I've not yet had the opportunity to run mine under load. I figure with the big neodymium magnets it should be a power house. Thanks for confirming that. :)

In my scooter I'm using the 6Ah bricks akin to yours, the PSH-1255F2-FR, in an isolated parallel configuration. They're the only decent high-rate batteries that I could fit in my scooter without physical modification, and since they support the same 3C/10C characteristics, I wanted to be able to split my drain across them to keep them under 3C at max for best range.

In about the same amount of space (a little more) I've gone from 24v @ 288 Wh to 36v @ 432 Wh. The scooter is almost done, I just have to get a couple beefy diodes and install my fuses and a couple other odds and ends and get some new chain. Can't wait to see what this monster does when I'm done! :)
 
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