raising voltage to maximize regen. braking?

[John in CR]

...But, the controller converts that Vphase x Iphase to Vbatt x Ibatt. So the higher the battery voltage, the lower the battery current to maintain that relationship...

Why try to over-complicate it? That doesn't change braking torque one little bit. It's still the same rpm, same braking torque, same current from the motor, so same power from the motor for that braking force. So what that the buck converting controller has a change in mix of the output to charge the battery. That doesn't change braking force, which is what the OP wants to do.

I already explained how to easily change the braking force quite simply, but instead let's over analyse something that won't work to accomplish the goal.

 

[serious_sam]

Why try to over-complicate it? That doesn't change braking torque one little bit. It's still the same rpm, same braking torque, same current from the motor, so same power from the motor for that braking force. So what that the buck converting controller has a change in mix of the output to charge the battery. That doesn't change braking force, which is what the OP wants to do.

I can explain it to you, but I can't understand it for you.

 

[retrocycler]

Been away from this for a while, sorry. But it is still a problem I'm trying to solve.

John and Serious Sam, you two have got me totally confused now!

I'm inclined to believe Serious Sam, because his is the answer I would like to hear, LOL.

But even Serious Sam is being ambiguous (or I just don't understand).
In one sentence S.S. says, "But, the controller converts that Vphase x Iphase to Vbatt x Ibatt. So the higher the battery voltage, the lower the battery current to maintain that relationship." Then a few sentences further on, S.S. says, "...if you used those extra cells in parallel with the pack (instead of series), you would also increase regen capacity of the pack by the same amount..."

Which sounds to me like in sentence one: higher voltage battery allows more current flow, ergo more torque...
and in sentence two: arranging cells to be higher voltage (less parallel) does NOT improve regen. capacity (what is that? torque?).

So thus I am now going to just go ahead an order a higher voltage battery (with the same capacity), and see what happens. I'll also report back here what I discover, of course.

I wish you all a fine thanksgiving!

 

[serious_sam]

But even Serious Sam is being ambiguous

Basically, more cells equals more capacity for energy and power.
- If you add them in series, it will have a higher voltage, thereby increasing power capacity.
- If you add them in parallel, it will allow more current, thereby increasing power capacity.

The controller converts between motor current & voltage to battery current & voltage. But on both sides, the power is the same (minus efficiency losses of course).

I think where there is a disagreement/miscommunication is that it isn't 100% clear exactly what is causing you to hit a limit.

-Is it the controller phase current limit - in this case, a relatively easy way to resolve it is to do a shunt mod like john said.
-Is it BMS current limit (and indirectly the battery current limit). In which case you need to replace (or modify/adjust if possible) the bms, and increase the capacity of the battery pack. Series or parallel.
-If the problem is something else, maybe there is a different solution.

The solution will depend on the root cause.

 

[goatman]

its a phaserunner controller thats being used, did you try 20 amps regen yet?

 

[retrocycler]

It is a phaserunner, and it is the phaserunner that is limiting current. I've programmed it to limit to 5A, 10A, and 20A. In all cases it correctly limits the regen. current to those values. (The fact that it then "lets go," and the regen. is abruptly cancelled is apparently a bug in the phaserunner. Grin tells me that it should reach the limit and then hold regen. to that limit, not simply quit regen. altogether).

I've just ordered a 52V "High Power" Li-ion battery (9.8Ah), to replace my 36V LiFePo pack (10Ah). Curious to see what happens. Grin says if the problem persists with my new battery, they will take back the Phaserunner (they think it might be the BMS fault).

Just by the way, the Ping LiFePo pack is pretty amazing. It has the V5 high power BMS. I can run the motor up a hill at 30Amps (!) for thirty seconds, and then when I stop to feel for temperature at the battery, I feel hardly any warmth in the pack or BMS. Based on this experience, I upped the regen. current limit to 20A, because I doubt it would stress this battery all that much.

Looking forward to a new run of experiments with my new battery, but that will not be for several weeks, I expect.

 

[retrocycler]

Update: I have been running on a new 52V battery, with similar Ah capacity to the prior 36V battery. The answer to my original question is now absolutely clear: I get STRONGER REGENERATIVE BRAKING with the 52V battery, at comparable amperages compared to the 36V battery. The Phaserunner still cuts out at the set power limits, which it is not supposed to do. I'm still trying to figure out why. Grin has not taken the phaserunner back yet, instead asking me to do some more experiments with it.