# Help with Regen Voltage Regulation!



## DavidDymaxion (Dec 1, 2008)

If you don't care about wasting power, you could put power resistors in series with the diodes in your schematic. That's not very sophisticated but it would be simple.


stevet47 said:


> I need some help from people much smarter than myself...so I have come here.
> 
> I am not building an electric car, but I am trying to build a regenerative braking system for a small 24V application using Li-Po batteries.
> 
> ...


----------



## piotrsko (Dec 9, 2007)

quick and dirty but may not be cheap: the internet and even Radio shack has 3 pin variable voltage regulators in a To-72 case or a TO 25 case. Some of these are good for a couple to about 10 amps a piece, but they stack in parallel (not to MIL-spec standards). How well they regulate, whether they are shunt or not requires further research. They can be had for about $3.00 USD each.


----------



## bjfreeman (Dec 7, 2011)

to be in parallel for proper charging you need both the minus and plus at the same potential. so the minuses are hooked together and pluses are hooked together
this might help.
http://www.zafr.com/trucktcom/parallel_sw.htm


----------



## stevet47 (Feb 27, 2009)

bjfreeman said:


> to be in parallel for proper charging you need both the minus and plus at the same potential. so the minuses are hooked together and pluses are hooked together
> this might help.
> http://www.zafr.com/trucktcom/parallel_sw.htm


The schematic shows the batteries in parallel when the Brake switch is closed, so I am not sure what you are saying. I'm not sure what 'potential' means. The link you provided is interesting, but as far as I understand it, my batteries are in parallel. Can you explain more?


----------



## stevet47 (Feb 27, 2009)

piotrsko said:


> quick and dirty but may not be cheap: the internet and even Radio shack has 3 pin variable voltage regulators in a To-72 case or a TO 25 case. Some of these are good for a couple to about 10 amps a piece, but they stack in parallel (not to MIL-spec standards). How well they regulate, whether they are shunt or not requires further research. They can be had for about $3.00 USD each.


I started looking into this option last night. What do you mean by "but they stack in parallel"? And why do you say it may not be a cheap option? $3 sounds pretty cheap to me. Are you saying I would need more than 1?


----------



## stevet47 (Feb 27, 2009)

DavidDymaxion said:


> If you don't care about wasting power, you could put power resistors in series with the diodes in your schematic. That's not very sophisticated but it would be simple.


This would certainly be the easiest option, but I am concerned that both this option and voltage regulator option may not be a safe way of charging Lipo batteries. 

Has anyone used a simple circuit like this before for lithium batteries? I am concerned they will not charge safely.

The other option I see is adapting a ready-made lipo charger, and using the power out of the motor, as the Vin for the charger, the only issue is that I need to find a charger than works on DC in.


----------



## bjfreeman (Dec 7, 2011)

stevet47 said:


> The schematic shows the batteries in parallel when the Brake switch is closed, so I am not sure what you are saying. I'm not sure what 'potential' means. The link you provided is interesting, but as far as I understand it, my batteries are in parallel. Can you explain more?


The schematic is for changing from parallel to series. and when relay is activated changes to series.
so all you have to do is change the wiring in the diagram so when the relay is activated the batteries are in parallel, otherwise they are i series.
just one relay


----------



## stevet47 (Feb 27, 2009)

bjfreeman said:


> The schematic is for changing from parallel to series. and when relay is activated changes to series.
> so all you have to do is change the wiring in the diagram so when the relay is activated the batteries are in parallel, otherwise they are i series.
> just one relay


Oh... you are suggesting that I replace my schematic with this one, in order to accomplish what I need with 1 relay instead of two switches. Am I understanding you correctly now?
Sorry.. I suppose I am thick headed tonight.


----------



## bjfreeman (Dec 7, 2011)

stevet47 said:


> Oh... you are suggesting that I replace my schematic with this one, in order to accomplish what I need with 1 relay instead of two switches. Am I understanding you correctly now?
> Sorry.. I suppose I am thick headed tonight.


you can use a switch if you want, it would work the same.
yes I get that way sometimes. no problem.


----------



## Ziggythewiz (May 16, 2010)

stevet47 said:


> Oh... you are suggesting that I replace my schematic with this one, in order to accomplish what I need with 1 relay instead of two switches. Am I understanding you correctly now?
> Sorry.. I suppose I am thick headed tonight.


Except that that schematic actually uses...6 relays...but who's counting?


----------



## DJBecker (Nov 3, 2010)

What's the application? Is it entirely battery powered?
If so, you don't need to worry about overcharging. Any power returned through regeneration will be a modest fraction of the power already drawn from the battery. You'll be unlikely to return enough current quickly enough to stress the batteries.

I suspect that you'll be pretty disappointed with the regeneration braking you can get with half pack voltage. You'll probably find that apart from an initial jerk, there is barely any braking effect.


----------



## stevet47 (Feb 27, 2009)

DJBecker said:


> What's the application? Is it entirely battery powered?
> If so, you don't need to worry about overcharging. Any power returned through regeneration will be a modest fraction of the power already drawn from the battery. You'll be unlikely to return enough current quickly enough to stress the batteries.
> 
> I suspect that you'll be pretty disappointed with the regeneration braking you can get with half pack voltage. You'll probably find that apart from an initial jerk, there is barely any braking effect.


Yes it is entirely battery powered, so you are correct, I will always draw more power than I can recapture, so you are correct in that I cannot overcharge the batteries as far as voltage goes, but I wasn't sure about charge currents. I believe max safe charge current is 1A, while the motor could be drawing 6A+ under load. I am unsure as to how fast that current drops off, so I don't know if I need to worry about that or not.

As for being disappointed, technically, I just need to prove that the concept works, but of course the higher the efficiency the better. How would you recommend I go about it? It would complicate things, but it may be possible for me to split the battery bank into individual 3.7v cells. This would give me 6 3.7V cells in series for power, and 6 3.7V cells in parallel for regen. That should allow me to recoup more lost energy, no?


----------



## DJBecker (Nov 3, 2010)

Recharge current and efficiency will depend greatly on the motor characteristics. But efficiency will be reduced somewhat by feeding into a fixed lower voltage.

You'll quickly decide that you need a PWM boost configuration, both to control the regeneration rate and to continue to withdraw power to low RPMs.


----------

