Has anyone got any suggestions on how to build a simple discharger for a 9s or 10s battery. Like the Foil drive one but to support bigger packs. I have 4 batteries now and occasionally when I charge them all up I don’t get to use 1 or 2, then it’s a couple of weeks before I can next use them.
Just want to discharge to storage voltage. Thought about making a simple DC powered fan or something with an xt connector on it but requires me to monitor and disconnect at the right time.
Cheers
If you use an RC style bancing charger, you can charge an empty battery with a full one.
Cool thanks I’ll look into that. Do the packs have to be the same number of cells? Assuming that’s the idea of the balance part of it?
If your running vesc you can use the open_loop command. It will use the motor as a heat sink with out spinning the motor.
Other wise connect three 12V 50W halogen bulbs in series (36V, 150W) and set a timer. And then set another timer so you don’t over discharge the battery.
It depends, banancing RC chargers have an input voltage range, you need to stay within that range. Make sure not to deep discharge the battery (lipo beeper on the balancing connector of the source battery might help).
If the battery to charge has a built in BMS, you can‘t use this method as the supply voltage has to be ecactly #S x 4.2V of the batttery. You would need a DC-DC converter but this would be overkill…
Thanks. I’m not running Vesc unfortunately.
Will look into the 150W lightbulb jig. Any idea roughly how fast that would discharge a fully charged 10s pack? Ideally I would be able to use it to bring my 10s packs down to 37V and my 9s packs down to 33V. No idea what sort of time that might take.
The math is is super easy,
Look for the Wh capacity of your cells, a 2170 molicel is about 15Wh.
Then 10S x 5P (if you had a 10S5P pack) x 15 = 750Wh for your whole pack.
At 150W draw it would be completely flat in 5 hours (750Wh/150W). So an hour on the discharger would be enough to get it down to 80%. 2 hours to 60%.
Discharging my 6S packs to charge my 7S packs.
I set the LiPo beeper to 3.7V. You need to be around to swap the source when the beeper starts. I was charging 2 7S LiIon@10A each from one 6S pack, thischarge current was 22 A, much better than the 2A with the charger.
I hook my batteries up to a 48v solar inverter and just run some standard lights from the inverter. Its got a programmable low voltage cut off on the inverter so I set it to my storage voltage and it automatically shuts off at the right storage voltage for my batteries.
just check the voltage range on the inverter is right for your battery voltages. You might need a 24v inverter as the one I have only goes down to 36v.
Another option I was thinking of, similar to sat_be’s suggestion above, many battery power stations include a DC input option for charging the battery bank off solar panels. Some people will attach an extra external battery to this input to “expand” that power bank capacity. I think this could work to discharge an eFoil battery as long as the power bank supports the voltage and then (most of) the energy is available for use. Not sure about stopping at a desired storage voltage though, which is an important part of the process. But I’m sure there are ways to set up a voltage switch without needing to manually unplug it.
Hello everyone.
I would like to show you my simple solution for discharging my 10S or 12S batteries to storage cells 3,75V.
I got a 48V / 600W heating cartridge for this.
[https://a.aliexpress.com/_EJOKPGx]
For the first test I set up a setup with 3L of water in a pot, a voltmeter, a current clamp and a temperature meter.
After everything worked very well, I got myself a small voltage display.
The voltage display can be configured very easily. For 10s or 12s, I set the low voltage on the display. When the voltage is reached, a beeper goes on. When the discharge process starts, I set a timer.
Great advice on a few discharge rigs, thanks. I have wired up a 150W 38V heater plate which works pretty well if i just put a small pot of water onto it. Otherwise will burn out without any way of pulling heat off it / thermal management.
Thoughts on something like this to use as a set voltage cut-out?
https://shorturl.at/uxayY
It looks like it has the necessary voltage detection with a read out
I wonder if my setup just needs something like this wired in then i wouldn’t have to worry as much about setting 3 alarms.
Just picked this up to test batteries and it works up to 200V. $43usd, not bad and works well so far. It discharges at a maximum of 150 watts and has a low voltage setting so it will automatically stop discharging at whatever you set it at.
MakerHawk Electronic Load Tester… Amazon.com
That looks like it would do the trick! Pretty easy to set discharge current / target voltage cutout etc? I have 2 x 10s packs and 2 x 9s packs so very seldom will go through them all in one session. Hence the need for a reliable discharger. The one I build is also 150W but has no controls.
