24v controller running 36v what about low battery cut off??

[rbelisle1]

I have an evg ebike that I rebuilt with a standard Razor 24 volt 20 amp controller which has a 20 volt low voltage cut out. The batteries I am using are 12v 12 amp SLA's. The controller works great for this bike. The motor is a Heinzman with a 21 amp mfgr's rating, so the two live nicely together. I have now bumped up the voltage on the bike to 36 volts. If I understand right, the low voltage cut out is now "worng" for my 36volts and If I am not careful, I could discharge my SLA's to the point of damage and or limit their lifespan. Is this correct??? In addition, what is the relationship of the 20 amp limit, now that I have bumped up the voltage. Is the motor still protected by the 20 amp shunt, or is it in danger of over amperage??? I dont quite get the VA thing, once you start upping the voltage.

The next question is about battery managment. So, lets say I am running along at 24 volts for a couple of miles. Lets say that the SLA's are at 11 volts each and then I switch in my fresh extra 12 volt battery. Won't the new battery feed some of its voltage into the old 24 volt stack. I am guessing that the new 12volt would see the other batteries as a load and try to feed them voltage, untill all three batteries sort of equal out, lets say somewhere near 11.5 volts.... correct???

Now for the wire size question. Looks like the bike was wired with 10 or 12 gauge battery wires. With the new higher voltage, do I need to go up a gauge or two, or since the voltage and total amperage is higher, can I get away with the stock wire size ??? I realize run length is an issue, but the new wiring added a minimal amout of wiring so I am not concerned with that.

thanks in advance.
Bob in phx.

 

[gmouchawar]

Bob.

You are correct the voltage cutoff will still remain at 20V and you do risk overdischarging your 36V.
Your second theory is incorrect. Add a fresh battery in series to half discharge pair will not charge them.
You run the risk or overdischarging them more. The 2 old one will run out and the new one will still supply more current. Except that current is in the wrong direction for the old cells.
But that wouldn't happen if the voltage cutoff exists.
I wouldn't worry about the wire gauge. That bike is over engineered. Actually at higher voltages for the same power you have less current running in the wires.
Of course bigger wires is always better.
Keep that ebike alive. I have an ex-24V with a generic controller runnig at 36V and I get 16-18MPH for top speed. I get about 11MPH at 24V.
Regards

 

[dogman dan]

Agreed. you have to run all three batteries together or you risk killing some. If you get a new 36v lighted throttle, it will light up a low volt indicator at the time you really should quit riding, but stil have about a mile of range left. Or you could just monitor with a voltmeter till you get a feel for how much slower is time to quit. I always know when the light is about to go on on my trike. The motor should be able to take a whole lot more than you are dishing out with that controller, but you need to make sure the controller can handle more voltage. A lot of em can go 12v more, but I don't know about the one you have.