How to know if battery supports regen?

Batteries, Chargers, and Battery Management Systems.
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Swe
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How to know if battery supports regen?

Post by Swe » Dec 30, 2017 3:37 pm

Hi,
How do I know my battery supports regen? Is it depending of what BMS is used? I have a battery a few years old from BMSBattery "bottle-09". I have not opened it up to look at the BMS but according to the link below this is the BMS that I have. It has a charge and discharge port. And with regen how to know if it supports charging through discharge port? BMSB is not so great at answer questions... maybe someone here knows anything about this BMS?

https://bmsbattery.com/bmspcm/714-10s-1 ... s-pcm.html

Swe
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Re: How to know if battery supports regen?

Post by Swe » Dec 30, 2017 3:42 pm

I found this link and someone there says "A couple in parallel might work pretty well for a bigger DD, but the charging isn't through the output leads, so you would sacrifice regen if that were an issue."

Does not sound so good. Does it mean I can not use regen on this battery, or was this problem only if you had them in parallel?

https://endless-sphere.com/forums/viewt ... =4&t=62552

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dogman dan
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Re: How to know if battery supports regen?

Post by dogman dan » Jan 01, 2018 8:49 am

I'd guess on the no regen for you side. Some bms will still allow up to 5 amps in the output, but regen could be more than that. Not worth trashing your bms, since it stands between you and burning your house down.

There is of course, the bypass the bms to discharge solution, but then you lose lvc protection on the discharging. You could still have balancing on the charge if you do it that way.

Me, I'd screw regen till you get a battery designed for it. Charges through the output. My experience with regen was that you could just pedal a few blocks and save the same number of watt hours. Just use a tiny tickle of throttle to eliminate the cogging from the dd motor, and pedal like you had the throttle off.

Think about the math of it.. Lets say you ride with 50w of throttle on. if you have a 500 watt hour battery, you could ride for 10 hours on that battery, using the throttle to eliminate the DD drag. Obviously you won't be doing that! But if you tickle the throttle on the flatter parts and pedal, you can ride a half hour that way using only 25 watt hours. Call it 5 miles, if you are going 10 mph for that half hour. That's a pretty good range extension, for just 30 min of regular pedaling. Its more range than you will ever get from regen braking. Especially if you start to coast it down to those stops anyway. Tickle the throttle when coasting, to get that extra distance from the coasting.

Swe
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Re: How to know if battery supports regen?

Post by Swe » Jan 01, 2018 9:31 am

I will not do it mainly for the extra range of battery, even though I think will get a few % extra since it is a heavy cargo bike and I have a lot of small and big hills here.

I would do it to save my brakes because I feel I use them a lot to slow down the speed even in smaller hills because I don’t want to ride faster with the children. And then a little bonus to have a little extra range with my small battery.

Thanks for your answer, guess I just have to wait until I change battery or cells. They are a few years now but I can have them one more season I think.

billvon
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Re: How to know if battery supports regen?

Post by billvon » Jan 01, 2018 5:07 pm

Swe wrote:
Dec 30, 2017 3:37 pm
How do I know my battery supports regen? Is it depending of what BMS is used? I have a battery a few years old from BMSBattery "bottle-09". I have not opened it up to look at the BMS but according to the link below this is the BMS that I have. It has a charge and discharge port. And with regen how to know if it supports charging through discharge port?
Depends on the design.

Most common way to implement separate charge and discharge protections is with a single FET on each, each blocking the appropriate direction. If this is the case then the discharge port can carry as much charge current as discharge current but you will have no overcharge protection. In other words, it will work just fine as long as your controller does a good job regulating regen voltage. If it fails and you see an overvoltage AND the battery is near full you could see damage or a fire.

Note that even if you set regen to "off" you can still see regen if you exceed the base speed of the motor (i.e. you are going down a hill.) In that case you will be feeding back through the discharge port and there's not much you can do about it; the diodes in the controller FETs will conduct and feed back voltage.

If the discharge output has two back-to-back (NOT parallel) FETs then it will likely protect against overcharge there as well, in which case no worries.
--bill von

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dogman dan
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Re: How to know if battery supports regen?

Post by dogman dan » Jan 02, 2018 9:21 am

I'm sure there are bms hacks I'm unaware of, I'm no E engineer.

Open the battery up, and try to get a good clear picture of the bms circuits, including the labels where wires solder on. Others here may be able to tell you much more about if it supports regen now. Or can be modified with a simple fix.

One of the easiest might be to just replace the bms, with one that does definitely support regen.

The very easiest is just to add a new wire and plug for discharge, that bypasses the bms. Have the original one still go to a light on your handlebars. When that light goes out, STOP.

FWIW, the one really legit reason to desire regen is to add additional braking power, that does not wear out your pads. If you do ride fast, you will brake hard. Riding fast is very tempting when new to e bikes.

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