Can I drive my 60V controller+motor at 72V?

General Discussion about large electric scooters and motorcycles and other things with no pedals.
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Chah
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Can I drive my 60V controller+motor at 72V?

Post by Chah » Nov 09, 2017 7:01 am

I have a Chinese-brand electric scooter. I'm not able to get information on the controller and motor, but the battery is spec'd at 60V 20Ah. I opened the bike up and got to the outside of the controller box, but I haven't yet been able to take the controller out and open it up. I'm a bit wary because of the huge stack of undocumented wires coming out of it.

I also have a 60V Li-ion battery that I connected in parallel with the 60V SLA battery that is installed inside the bike. Fully charged the 60V Li-ion is 71.4V, meaning it should be 17S. I'm wondering what voltage would it be likely that I can drive the controller/motor for increased speed and power? I'm thinking that in all likelihood, I could get away with 18S for a max/nominal voltage of 75.6V/66.6V. I suspect I could get away with 19S or 79.8V/70.3V.

Does anybody have any ball-park idea how far it is safe to take the controller voltage to, given it's rated for 60V?

Voltron
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Re: Can I drive my 60V controller+motor at 72V?

Post by Voltron » Nov 09, 2017 9:16 am

I've been running my generic 60v controller at 20s without problems, but it has 100v capacitors. I just opened up another 60v controller from a different generic scooter, and it only had 82v caps, so unless you open it up to check there's no way to be sure.

Either way, you really have to keep any eye on your voltages during running, as the low voltage cutoff will be wrong, and you can over discharge your battery.

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fechter
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Re: Can I drive my 60V controller+motor at 72V?

Post by fechter » Nov 09, 2017 9:22 am

A 60v lead acid battery will be around 72v when fully charged, so the controller has to be made for at least this much. Usually there is a little headroom in the ratings also.
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billvon
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Re: Can I drive my 60V controller+motor at 72V?

Post by billvon » Nov 09, 2017 9:52 am

Chah wrote:Does anybody have any ball-park idea how far it is safe to take the controller voltage to, given it's rated for 60V?
In general 100V is a common spec for caps and FETs, so at 72 volts you have ~30V of headroom. However some parts are rated at 80V so be careful.

Other potential issues:
Higher voltage means higher power in the controller
Might mean higher dissipation in the housekeeping supply (especially if it's a cheap linear)

Overall the risk is low but not zero.
--bill von

Chah
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Re: Can I drive my 60V controller+motor at 72V?

Post by Chah » Nov 09, 2017 11:33 am

Voltron wrote:I've been running my generic 60v controller at 20s without problems, but it has 100v capacitors. I just opened up another 60v controller from a different generic scooter, and it only had 82v caps, so unless you open it up to check there's no way to be sure.

Either way, you really have to keep any eye on your voltages during running, as the low voltage cutoff will be wrong, and you can over discharge your battery.
Thanks for the info. Do you have any tips on opening up a controller that you are unfamiliar with? There are so many wires coming out of there, I'm worried about disconnecting everything and not being able to put it back correctly. Are the capacitors the only thing I need to check in there?

Noted on the low voltage cut-off. I drive to and from work and recharge at work. I've checked the voltage and I'm always above 60V when I start the recharge, so I'm not going near the LVC.

Voltron
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Re: Can I drive my 60V controller+motor at 72V?

Post by Voltron » Nov 09, 2017 3:14 pm

Still, as you go up in voltage you might be up too high for it to cut off in time.... plus, you're measuring at rest, and the voltage can sag considerably while running esp with a heavy scooter, which might not damage the lead acid half but the lithiums might not like it. I mention it as I recently killed a few batteries wiih some unintentional low volting, and it took way less then I would have thought to kill a couple of groups.

Chah
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Re: Can I drive my 60V controller+motor at 72V?

Post by Chah » Nov 09, 2017 6:54 pm

Thanks for the warnings. Yes as I go up in voltage, I will definitely not be able to rely on any controller-warnings to determine when to recharge. However right now I'm in the process of trying to install a no-name meter that measures real-time voltage and current: https://item.jd.com/15359070342.html. When that's done I will know both the open circuit and the under-load voltages. For this, I'm going to be cutting and joining wires outside the controller, not getting inside the controller itself.

Since we're on this topic, maybe I just share my thoughts for any feedback as I don't know if it's been done the way I'm thinking before. This meter needs to run 3 wires from inside the bike to my dash where I'm going to mount the meter. Further it needs 2 more wires for power (between 4 and 28V) which I'm going to take from a 9V battery, located on or near the dash. The 3 wires I need from inside the bike are the 2 sides of the shunt, and the V++ wire (the high voltage wire between the battery and the controller/motor. The shunt needs to be inserted in the V-- wire (the low voltage wire between the battery and the motor/controller) for indirectly measuring the current. So I need to cut and reattach that V-- wire to the 2 sides of the shunt.

There are a couple of things I want, that I think I have a solution for:
1) I want to have the wires grouped together in some kind of outer sheathing, so I don't have to run 3 individual wires from internal to the bike, up to the dash
2) I want the system to be easily connectable/disconnectable so I can take the meter off my bike when I'm not there and just not mount it if it rains.

My solution is to buy any cable that has multiple (at least 3) wires inside and of about 1.5m in length that has a male connector on one end, and equivalent female connector of the same type on the other end. I'm going to cut this cable in the middle at the appropriate position exposing the wires inside. The longer side of this cut cable I'm going to solder them to the appropriate wires inside the bike, and I'll run the side with the connector attached, out to the dash. The other side of this cable I'm going to solder to the appropriate wires inside the meter, with the opposite connector attached to the other end. Now when I connect these two together the appropriate wires in the bike will be connected to the appropriate wires in the meter. And I can disconnect the meter and take it off the bike as I wish. I'm thinking of buying an ethernet RJ45 extension cable with male and female connectors on either side, because ethernet has 8 twisted pairs inside, more than enough for the 3 wires that I need.

Any comments on whether this plan will work?

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