jana
10 W
Really twisted my mind on how to discharge 3 4s 5000mah Lipos in series.
Quite happy withthis simple sollution pulling nearly 300W
Quite happy withthis simple sollution pulling nearly 300W
Easy battery discharge setup
- Thread starter jana
- Start date
SamTexas
1 MW
That's good. I'd be a lot better if discharging is stopped automatically when certain voltage is reached.
jana
10 W
Yes I agree, but I don't know how to make that i 5 minutesSamTexas said:
I tried to stop the discharge at 3,5v, but even when looking closely one cell came down to 3,4.
A stop watch is essential and even then it is risky.
vodk1c3
100 W
Haha !! Nice!
999zip999
100 TW
Yes don't walk away.
recumbent
100 kW
I connect my battery packs to a hairdryer and the balance leads to a Celllog.
This way you can either hear the dryer slowing, or the Celllog beeping when one cell reaches low voltage cut-off.
But I'm usually soldering other stuff at the same time and monitor closely.
This way you can either hear the dryer slowing, or the Celllog beeping when one cell reaches low voltage cut-off.
But I'm usually soldering other stuff at the same time and monitor closely.
Well, if you set up a zener and potentiometer (to "tune" the turn-off voltage) on each of the cells, with an optocoupler's input shorted out by the zener's output, and all the opto's outputs wired together so that any one of htem that turns on shuts off the drain (via relay, etc).
While the cells are above the cut-off voltage, the zeners would draw a certain amount of current, limited by the potentiometer. The zener would maintain a certain voltage across itself. Once the voltage of a cell drops below that point, the zener on that cell wouldn't be able to sustain the voltage and it would allow the opto output to turn on, shutting off the load.
You'd want to use a latching relay or whatever on the load so it can't turn back on after the cell voltages spring back up.
Exactly how this owuld be wired up, I'm not sure--it might be more complex than I'm thinking.
The bad part of this is that the zeners will continue to load the cells down so it cannot be left unattended, and you must still monitor the pack.
If you are willing to make the system even more complex, you can install relays between each cell and it's zener, so that when the load is disconnected so are the zeners.
Alternately you can "copy" parts of the Fechter-Goodrum BMS, just for the LVC part, and use that for your load cutoff.
While the cells are above the cut-off voltage, the zeners would draw a certain amount of current, limited by the potentiometer. The zener would maintain a certain voltage across itself. Once the voltage of a cell drops below that point, the zener on that cell wouldn't be able to sustain the voltage and it would allow the opto output to turn on, shutting off the load.
You'd want to use a latching relay or whatever on the load so it can't turn back on after the cell voltages spring back up.
Exactly how this owuld be wired up, I'm not sure--it might be more complex than I'm thinking.
The bad part of this is that the zeners will continue to load the cells down so it cannot be left unattended, and you must still monitor the pack.
If you are willing to make the system even more complex, you can install relays between each cell and it's zener, so that when the load is disconnected so are the zeners.
Alternately you can "copy" parts of the Fechter-Goodrum BMS, just for the LVC part, and use that for your load cutoff.
docnjoj
1 GW
kfongs LVC Smart Switch would work for this too. You would have to set both the time and the voltage and periodically push the on button to keep the switch active. It would cut off when one cell hit the LVC first so set it at say 2.85 for LifePo4. It is pack level rather than cell level but much better than staring at the pack for a couple of hours. Boring! I use my hotplate resistor that gives about 5 amps @ 36 volts nominal. It also will datalog for the pack.
otherDoc
otherDoc
parabellum
1 MW
Be careful, I damaged my iron this way. Those temp interrupters/switches inside are not made for DC current and easily weld together (at higher voltages). In my case it was 24s LiPo pack on 110V iron. I think the trick is not to get to the temperature where switch is activated.jana said:Really twisted my mind on how to discharge 3 4s 5000mah Lipos in series.
Quite happy withthis simple sollution pulling nearly 300W
SamTexas
1 MW
That's new for me. Why do they (interrupters/switches) react differently on DC?
Because AC switches don't have to separate as far to break the connection, because AC goes down to zero volts twice every cycle (running at 60hz in the USA).
DC switches ahve to move their contacts farther apart to break the arc between them as they separate.
Running DC thru an AC-designed switch or relay or circuit breaker might nto be able to break the circuit at all, if at the same voltage in DC it was originally intended to run AC at, or may only be able to do so a limited number of times before the contacts are burned enough to fail to make contact, or actually weld together and be unable to break the connection.
Sometimes the design is such that they work fine either way, or at least when used at a lower DC voltage and current than the AC ratings it has. That's why you will see some switches and relays marked for both, but usually with lower DC than AC limits.
edit: wikied
http://www.endless-sphere.com/w/index.php/Switches_(AC_and_DC)
DC switches ahve to move their contacts farther apart to break the arc between them as they separate.
Running DC thru an AC-designed switch or relay or circuit breaker might nto be able to break the circuit at all, if at the same voltage in DC it was originally intended to run AC at, or may only be able to do so a limited number of times before the contacts are burned enough to fail to make contact, or actually weld together and be unable to break the connection.
Sometimes the design is such that they work fine either way, or at least when used at a lower DC voltage and current than the AC ratings it has. That's why you will see some switches and relays marked for both, but usually with lower DC than AC limits.
edit: wikied
http://www.endless-sphere.com/w/index.php/Switches_(AC_and_DC)
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