MrDude_1
100 kW
First lets get the disclaimer out of the way.
This is a stupid idea. If it fails, there is a high chance you will damage your batteries. There is a chance you could explode something. This works with high DC voltages, High AC voltages, and is lethal in just about every bad way possible. If done incorrectly it could even be non-isolated and therefore touching the case/cover/whatever could kill you. plugging in the battery/power in the incorrect order, could kill you... Worse case, it isnt you but your burn down your house with your dogs, cats, kids and wife. Dont do this unless you understand it and didnt need this thread in the first place.
Ok, with that out of the way, heres my dumb idea. I want to build a charger that monitors the voltage at the cell level, keeping a Constant Current into the battery without the current tapering off as overall voltage rises. Yes, charger voltage output will exceed battery max voltage. However it will monitor the voltage of each cell, and maintain that large current until they get closer to charged, then swap to a normal CV top off. This is like a "fast charge" on a smart RC charger, but scaled up to big boy size.
Since I am building this for myself, its going to work for 16s lipo, with enough headroom to allow 32s lipo in the future. Depending on scaling as I design it it may or may not allow lower cell/voltage counts
My current idea is to start with a microcontroller... set it up to read each cell and monitor the voltage at a cell level, the pack input voltage, and the amperage.
Then I will modify a meanwell so the "trim" of the voltage and current can be controlled with the micro-controller.
I can then start with the software... some simple safety catching.. etc. The software is the easiest part for me. Its what I've been doing for 17+ years.
The charge plan would go something like this...
Battery at 59v combined 3.6875 per cell.... desired charge is 66.4 (4.15v)
Turn on the charger, the charger will adjust to its programmed limit, say 20a... voltage would drop on the output below 66.4v... normal CC/CV charging so far.
Now as the battery comes up a normal charger would drop amps, but in this case, the controller would raise the desired voltage higher... so the pack input may read higher, but each cell is still well below the full voltage. if you take cell1+cell2+cell3+... you would get a lower number than the input voltage. I would keep doing this until one cell (any cell) reached its limit... in my mind I choose 4.10.
That would end my CC phase.
The microcontroller would then lower the charger voltage to match the battery final voltage... and finish as a normal CV charger.
This means that instead of charging the battery fast for the first half, then slower, and slower and slower... it would charge at a high rate almost the entire time, and then trickle. Cutting charging time almost in half in some cases.
later I could add code to balance, or measure all kinds of fun stats. but the basic design goal is to maintain the just under 1C rate charge as long as possible, before topping up.... instead of the "natural curve" of ohms law on a CC/CV charger.
So besides the obvious "you're going to burn your house down if you dont electrocute yourself first" here are the catches and gotchas I have so far on this whole thing.
1. if the controller is connected, it could see the higher then normal pack voltage. the input caps that are not rated high enough could blow.
2. the current and the voltage output need to fail safe... if they cut off, current needs to drop to min, and so does voltage... however this should not be set so low that it damages the controller (some can not have it set as zero)
3. this really only makes sense for large packs. small packs wont see enough of a change anyway.
4. I will have to keep in mind wattage limits... as the voltage rises with a constant current, total wattage will go UP instead of down. You can only pull so much from a wall socket.
5. If the power supply is marginal in capacity, it may be working now because it cools off as time goes on... now its work load will increase over time, so it may overheat.
6. ???? any other ideas
questions:
What effect does this have on the lipo? assuming we're staying well under the C rating for charging it, what effect does it have vs the normal CC/CV charging?
What are the gotchas? I realize I only have an outline up there, no code, no schematic, yet... but I have only been thinking about it since I found a nice circuit for a small bad-boy CC source (for emergency roadside charging).
also, have any of you loons done this before? :lol:
This is a stupid idea. If it fails, there is a high chance you will damage your batteries. There is a chance you could explode something. This works with high DC voltages, High AC voltages, and is lethal in just about every bad way possible. If done incorrectly it could even be non-isolated and therefore touching the case/cover/whatever could kill you. plugging in the battery/power in the incorrect order, could kill you... Worse case, it isnt you but your burn down your house with your dogs, cats, kids and wife. Dont do this unless you understand it and didnt need this thread in the first place.
Ok, with that out of the way, heres my dumb idea. I want to build a charger that monitors the voltage at the cell level, keeping a Constant Current into the battery without the current tapering off as overall voltage rises. Yes, charger voltage output will exceed battery max voltage. However it will monitor the voltage of each cell, and maintain that large current until they get closer to charged, then swap to a normal CV top off. This is like a "fast charge" on a smart RC charger, but scaled up to big boy size.
Since I am building this for myself, its going to work for 16s lipo, with enough headroom to allow 32s lipo in the future. Depending on scaling as I design it it may or may not allow lower cell/voltage counts
My current idea is to start with a microcontroller... set it up to read each cell and monitor the voltage at a cell level, the pack input voltage, and the amperage.
Then I will modify a meanwell so the "trim" of the voltage and current can be controlled with the micro-controller.
I can then start with the software... some simple safety catching.. etc. The software is the easiest part for me. Its what I've been doing for 17+ years.
The charge plan would go something like this...
Battery at 59v combined 3.6875 per cell.... desired charge is 66.4 (4.15v)
Turn on the charger, the charger will adjust to its programmed limit, say 20a... voltage would drop on the output below 66.4v... normal CC/CV charging so far.
Now as the battery comes up a normal charger would drop amps, but in this case, the controller would raise the desired voltage higher... so the pack input may read higher, but each cell is still well below the full voltage. if you take cell1+cell2+cell3+... you would get a lower number than the input voltage. I would keep doing this until one cell (any cell) reached its limit... in my mind I choose 4.10.
That would end my CC phase.
The microcontroller would then lower the charger voltage to match the battery final voltage... and finish as a normal CV charger.
This means that instead of charging the battery fast for the first half, then slower, and slower and slower... it would charge at a high rate almost the entire time, and then trickle. Cutting charging time almost in half in some cases.
later I could add code to balance, or measure all kinds of fun stats. but the basic design goal is to maintain the just under 1C rate charge as long as possible, before topping up.... instead of the "natural curve" of ohms law on a CC/CV charger.
So besides the obvious "you're going to burn your house down if you dont electrocute yourself first" here are the catches and gotchas I have so far on this whole thing.
1. if the controller is connected, it could see the higher then normal pack voltage. the input caps that are not rated high enough could blow.
2. the current and the voltage output need to fail safe... if they cut off, current needs to drop to min, and so does voltage... however this should not be set so low that it damages the controller (some can not have it set as zero)
3. this really only makes sense for large packs. small packs wont see enough of a change anyway.
4. I will have to keep in mind wattage limits... as the voltage rises with a constant current, total wattage will go UP instead of down. You can only pull so much from a wall socket.
5. If the power supply is marginal in capacity, it may be working now because it cools off as time goes on... now its work load will increase over time, so it may overheat.
6. ???? any other ideas
questions:
What effect does this have on the lipo? assuming we're staying well under the C rating for charging it, what effect does it have vs the normal CC/CV charging?
What are the gotchas? I realize I only have an outline up there, no code, no schematic, yet... but I have only been thinking about it since I found a nice circuit for a small bad-boy CC source (for emergency roadside charging).
also, have any of you loons done this before? :lol:
