Higher regen voltage than battery voltage

I have a 12FET 4110 Lyen controller, which seems to only offer 3 options for regen voltage in the programming software.
The options for regen are something along the lines of (not exact):
72V, 80V, 99.75V

Lyen did once mention to me how if I want regen braking while running the bike at 48V (12s), I can still use the 72V regen option, since battery voltage would be lower than set regen voltage, therefore regen would be activated...

...but this raises the question: Would using regenerative braking set for higher-than-battery-voltage be harmful to the batteries?
I have a 18s4p LiPo (Turnigy 5Ah 20C packs) battery config. I'm wanting to step down to 12S, to extend bike range, but want to keep regen. braking.

That setting is basically just an upper limit, and not terribly useful. As long as its set below the max voltage the MOSFET's can tolerate, its fine. You can run anything below that. The current going in, and resistance of the battery will dictate what the voltage rise is under regen. Those Turnigy cells have very low internal resistance, so it would take a MASSIVE amount of current to raise the battery voltage to dangerous levels. Typically not even possible, plus most controllers have a rather soft regen current limit of something like 10A. The only thing you need to be aware of, since it will 'allow' up to 72V or so, is you can theoretically overcharge the battery. In practice, this would mean you'd need a battery at 100% SOC, and then a HUGE steep hill, and ride regen the whole way down. Unlikely. Even at 4.2V/cell, you could ride regen down smaller hills fine as long as you have enough battery capacity so that the voltage rise isnt terribly significant. Some people like to avoid using regen right off the charger that run 24S LiPo, since that will create higher than pack voltage that could damage the 100V MOSFET's already near or beyond design spec. As long as you have 10-20% overhead, I wouldn't worry.

I only charge my cells to 4.10v/cell, so they have headroom even when 'fully' charged, and I don't worry about using regen RIGHT off the charger. But then again, I also have my HVC properly configured with XPD. It's still unlikely that would help much if for example, the battery connection was loose and I was riding REGEN at high speeds. Loosing the battery connection under load would likely create a voltage spike that can kill the MOSFET's before the controller even knows about it and has time to react.

Skedgy Sky said:

I have a 18s4p LiPo (Turnigy 5Ah 20C packs) battery config. I'm wanting to step down to 12S, to extend bike range, but want to keep regen. braking.

Click to expand...

Hi, Skedgy Sky

Volting down from 18S to 12S will not extent the range of your bike IF you are travelling at the same speed. In fact, the lower amps draw for the same power means that 18S has slightly less resistance in the power wires. So 18S gives a tiny bit MORE range than 12S, as long as you keep the speed the same.

Sounds like you'd benefit from a Cycle Analyst (if you don't have one already) and it's cruise control feature. 8)

@ZOMGVTEK
Thanks. I ended up using 18s regen while riding on 12s and no fires!

...although there is much less torque upon accelerating. After Holocene's post and me testing the range (to confirm what he says), I may very well end up going back up to 18 or 24s.

@Holocene
I had asked about this in another post... here: http://endless-sphere.com/forums/viewtopic.php?f=14&t=47310

I always seem to get higher watt hours per mile as I step up the voltage... it might be due to there just being more power available to me, and I use it as a result.
...something along the lines of:
12s: 32-40 Wh/m
18s: 42-55 Wh/m
24s: 55-70 Wh/m

But I just went out for a few test rides, and using the CA to limit my speed at around 20MPH, I collected the following data:


I tried being consistent with my riding style, and although the 12s data shows lower Wh/m, I think I was a little easier on the throttle on that run as it was my first time doing this test.

After seeing these almost-equal range results, I may end up using 24S, just for when I want or need the power. (This will however obviously put more stress on each parallel group)
Only problem now is to fix the grinding of my hub motor as a result of it warming up, and that problem is sure to come faster on my rides as summer approaches with me riding on 24S lipo.
( http://endless-sphere.com/forums/viewtopic.php?f=2&t=47408 )

Skedgy Sky said:

I have a 12FET 4110 Lyen controller, which seems to only offer 3 options for regen voltage in the programming software.
The options for regen are something along the lines of (not exact):
72V, 80V, 99.75V

Lyen did once mention to me how if I want regen braking while running the bike at 48V (12s), I can still use the 72V regen option, since battery voltage would be lower than set regen voltage, therefore regen would be activated...

...but this raises the question: Would using regenerative braking set for higher-than-battery-voltage be harmful to the batteries?
I have a 18s4p LiPo (Turnigy 5Ah 20C packs) battery config. I'm wanting to step down to 12S, to extend bike range, but want to keep regen. braking.

Click to expand...

The regen voltage limit typically only comes into play as far as the battery is concerned if you're starting out with a full charge at the top of the hill. One of my motor/controller combos regularly hits over 70A of regen voltage, and even accelerating slowly up to speed on a fresh charge and hitting the brake at high speed, I've never seen voltage spike to dangerous voltage as a result of "negative sag". That means the controller's limits are protected by the battery too.

All bets are off though if you're starting off at the top of a long steep hill. Harol_in_CR will have that as a regen concern, so he'll need to figure out what top of voltage to use for charging. His target will need to be what gets him to near 100% charge once he gets down to the main road.

My controller has regen, however the seller said it doesn't have, but I enabled it, the controller's low voltage cutoff is at 58V, it's marked as a 108V controller anyway and my fully charged battery is around 115V. The problem is that the regen doesn't work at that voltage. It works well with a 72V battery. When no battery connected, I measured the voltage and the voltmeter reads 90V, so that's the maximum voltage the regen can support and I want to increase it to around 115V. I looked up other threads, but my controller is not a common one, I have no information where the low voltage cutoff resistor is. I'm not sure it's marked R12 on my PCB and I don't want to blow it up, because it was not that cheap and I already increased the amps to 54A.

Edit: I see my problem is not really related, but my subject is the same, I want higher regen voltage than the battery voltage.

It might be helpful to know what controller you have. Most good controllers set the regen cutoff voltage with software, not hardware. the resistor they use to sense voltage will be the same they use to sense voltage for everything else.

perhaps the higher voltages and thereby lower amps means less energy is wasted through internal resistance, as power loss to heat is to the amps squared