Overvolting 48 - 68v?

[Sunder]

Hi Guys,

I made a throw away question in another thread about overvolting bikes and the suggestion was to pair an 8s with a 6s (so as to not over volt), but I thought I'd start a thread about it, since I really want to ask the question about serious over volting.

Rather than build a hybrid pack, I'm considering buying 2 x 8s packs to replace my 2 x 6s packs, mainly because at nominal voltage, I'm only getting 44v out of a 48v system.

However, that means at full charge, I'm actually putting 68v through a 48v system. That's enough to scare anyone... I know most systems have a tolerance range. For example, my "12v" inverter will take down to 10.8v and up to 15v before shutting down either way. My car fridge could be driven to 18v before it complained of over-voltage and shut down...

I've also been told by an electrical engineer that generally 20% over voltage is safe. However, I'm talking about a 42% over voltage.

Has anyone done this before? Or if you have over-volted, how much have you gone? I'm obviously not asking for guarantees, but I wanted to get a feeling for whether it's guaranteed suicide, a calculated risk, or reasonably safe.

 

[vanilla ice]

I have and it worked. I'd look at it as a calculated risk. I would guess you're more likely than not ok with those numbers. Remember SLA "48v" is really more like 55 volts.

 

[Sunder]

Awesome One vote for trying this.

Can I ask what brand controller you were using?

 

[wineboyrider]

Yes. Controller type information etc. The only way to know for sure is to open up and examine the caps. 8) 8) 8)

 

[Sunder]

Yes. Controller type information etc. The only way to know for sure is to open up and examine the caps. 8) 8) 8)

Could you elaborate on this? I'm assuming certain capacitors could take certain voltages, and part numbers would let us research?

Could installing a fan help with over voltage?

 

[wineboyrider]

Do you have an infineon stock 48v controller, a lyen any voltage (almost) controller, headline controller....? Inside the controller there is a cap that looks like a small can that has a max rated voltage. I have a lyen controller and run many different voltages all the time, depending on my trip etc. For example, I run 36v lifepo4 (45v), 36v lifepo4 with 5s lipo booster ( 65v), 36v with 6s lipo booster4 (70v), 12s lipo (50v), 11s lipo, 10s lipo. 8s lipo is 67.2 v off the charger so this would be pushing the limits of some stock controllers (unmodified). Most ebike kit companies don't want you to run more than 48v, because of legal issues...?

 

[theRealFury]

Motors are not voltage dependant. You could quite easily run an average motor on 12V @ 20amps or 120v @ 2 amps. Motors are power dependant so are wattage rated, and both of these examples are 240watts.

The only thing you really need to worry about is the controller. As stated you have to check the input capacitors (the largest capacitors in your controller) almost all capacitors have a voltage and a capacity rating on them such as 65v 1000uf. You need to make sure that the input capacitors in your controller are rated for more voltage than your fully charged battery pack. Also worth noting is that if you have regen braking capability then you have to leave some headroom on the capacitors for this as regen braking will increase the voltage by a couple of volts and might pop a capacitor if its close enough to the limit.

Basically if your capacitors are 65v then I would say 60-62v max to be on the safe side, any closer and you are risking it if you ask me.

 

[dogman dan]

I'd get another controller, and then just go for it at 18s. This is where you are going, even if you don't think so now. 8)

It can be pretty cheap, a lyens 9 fet 72v 20 amp controller will get you the speed, without the excess amps likely to melt a motor. You can safely let er rip with this little box. Gotta watch the motor heat like a hawk once you up it to the 12 fet 40 amps ones.

Cheap too, about 89 bucks.

No doubt the 63v caps on many controllers can take more, but some blow just running 12s too. Luck of the draw on chinese quality on caps.

 

[wineboyrider]

I'd get another controller, and then just go for it at 18s. This is where you are going, even if you don't think so now. 8)

It can be pretty cheap, a lyens 9 fet 72v 20 amp controller will get you the speed, without the excess amps likely to melt a motor. You can safely let er rip with this little box. Gotta watch the motor heat like a hawk once you up it to the 12 fet 40 amps ones.

Cheap too, about 89 bucks.

No doubt the 63v caps on many controllers can take more, but some blow just running 12s too. Luck of the draw on chinese quality on caps.

Exactly. I have blew one of my controllers on 12s lipo and the caps were rated for 62v. Actually, Lyens 9fet controller can take 100v! I have run 36v lifepo4 and 12s lipo into mine and it will make any motor hum. I think the max amperage (at least on mine) is closer to 25 amps, but I limit mine to 20 amps and lower for the ping's sake. 95v x20 amps= 1800 watts though and that's enough to cook a 9c on a good trip though