Was thinking I need to get a “not a bomb” sticker for the box I put my homemade cnc power supplies and controller in.
Interesting topic though glad I didn’t miss this one entirely.
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After this new wave of 12s12p boards that’s apearing recently I have been thinking alot about battery packs. These extended range packs seem like a far better idea for riders that only do long rides occasionally and not for their ever day commute.
i have been thinking about an alternative way to achieve this but I need something that I’m having issues sourcing, maybe one of you knows the answer.
I’m looking for a current limiter board. Basically the constant current section of one of these boost converters but without the boost. I want to be able to limit current flowing into a pack in an efficient way. This seems like a simple task but I can’t find a good solution.
Any ideas?
Maybe not what you want, but my plan for this issue.
In my view all of the DC-DC converters are terribly inefficient, you can see by the amount of heat they produce. The best way is to connect the batteries directly in parallel, but this cause a situation that if the diference in voltage is too big it will create a massive surge of current that can damage either battery and has potential to melt thing and create a fire
The solution is to have a micro controller on the external battery that compares both voltages and only enables the bridge between them if the diference is bellow a set value
To calculate it we just need to know the configuration of both packs and the internal resistance of each cell (ignoring that it is also a function of state of charge, we do the math with the lowest value to be safe)
Doing that we can calculate the maximum allowed voltage diference and also how the current will be split during use between the main and external pack
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Do you use your pack at the start of your ride when battery is still around 90-100%? Have you tried starting using it when your pack was already around 20-40%? Does it make any difference or does the whole contraption heat up more?
Yeah this is what I was thinking.
So this is why I was trying to find an efficient method for limiting the current. If we had this then we could make a cable which would allow using any 12s pack to add capacity to any other 12s pack. Once connected the external pack would charge the internal until they were at the same voltage then they would run down in parallel. Any large loads would cause the internal pack voltage to dip but then it would be replenished from the external pack once the load is lowered again.
Additionally this circuit would allow charge rate limiting from a wall supply of you don’t want to charge at full speed.
The only way I see if doing this other than the circuit that only connects if they are close is the DC-DC converter itself or a large resistor, both with the same efficiency problem
Yah the DC voltage dropping part is called a buck converter I just ordered one that says can deal with up to 60V on the input side trying to drop it down to somewhere around 4V to power LEDs in my riser directly from the main batteries instead of having its own battery.
^^ says should be about 70-80% unfortunately no idea when mine will be shipped so have to wait to see how it actually works out.
Yeah I don’t really want to drop voltage that much, just limit the current.
However today I had a crazy idea . . .
Vesc has configurable current limit and is able to be configured for DC motors which is basically just a current controlled DC power supply right?
If so you could use an old FOCBOX as a constant current power supply to charge another battery from. Hmmmmm . . .
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Oh right just saw DC to DC being discussed in last couple posts wasn’t thinking of the context of the thread so much as my recent purchases 
That said lower the voltage difference is going to in effect limit the current flowing from one battery to the other as well no?
@DerelictRobot How’s the mppt controller working out? A friend wants me to build a range extender for her evolve carbon and I like the look of your controller…
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Thanks to everyone in this thread who shared their knowledge.
My inelegant charge and ride setup. Been tested for the past few months.
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Late reply, I have @DerelictRobot s charge and ride. Still kicking. I let my evolve and ownboard friend use it. I put it in Blue shrink wrap.
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I want a redbull now
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And vodka
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Make it a double
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So long as the auxiliary battery has the same or very close to the same voltage when initially connected there should be no issues connecting, then discharging two batteries in parallel.
Provided they both have the IR to easily supply their proportion of load (calculated by a ratio of their capacities) there should be no issue. The two packs will just stay at identical voltage the whole time.
If the setup is attached to the board anyway I’m at a loss about why it wouldn’t just be connected in parallel. No need for anything other than connectors.
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Exactly, just don’t mixture cells with different base chemistry, like Lipo and Li-ion or LiFe
That is possible, but you have to mach both fully charged and fully discharged values with different series configuration
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I built something like that with my old battery pack and a power booster, but i was a bit worreid about the impact of charging while riding both on the BMS and battery, what are your feedbacks on that ?
Also interested in if there is a best practice here for at what point in the boards voltage that you hook up the ranger extender? Someone above brought up regen being a concern, so building on that if I just built one of these extenders and then only hooked it up after my board was at like say 80%, I shouldn’t have an issue?
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