Upload Your Circuit Schematics & Requests Here...

[kwheels]

This is probably really simple, really bad, and has been uploaded before....but
Heres my schematics to run the Kelly KDS48200 at 48V with SLA's

edit: its based off of the schematics that kelly provided, but with a circuit breaker instead of a contactor....its essentially a simplified version of theirs, with no reverse circuit for a fixed magnet motor

[spinningmagnets]

Circuit request...I'd like a schematic for a pigtail (to be connected permanently on the controller) in between the controller and battery, so when someone tries to plug the battery in backwards they don't fry the controller.

Red and black, of course, and polarized Anderson plugs, but I can visualize someone getting a new battery pack, and attaching their own plugs (in an attempted upgrade), but they end up attached backwards...

[amberwolf]

Well, short of a diode in series with the pack, which will have to be capable of handling the entire battery current supplied to the controller, the only other way is a diode reverse polarity *across* the terminals, and a fuse in series with one or both of them.

That way if it's plugged in backwards, the diode will bring the voltage across the controller inputs down to the diode drop (around a volt at high currents like this), and the fuse will blow from the current (which will be whatever the max the battery is capable of putting out when shorted like this).

Schematic to come when I get my trackball cord working long enough (yet more of my bad luck run, I guess).

EDIT: I guess if i hold the cord right it works, so:

battery protection.PNG (4.03 KiB) Viewed 122 times

[fechter]

There is another way. In this configuration, the FETs are being used as "ideal" diodes.

If the battery is connected properly, the FET will turn on. In reverse, the FETs stay off and nothing blows up.
The problem here is the FETs have to handle the full load current, so you may need many in parallel to keep the heat down. Using a very low on resistance FET helps too. I usually estimate about 20 amps per IRFB4110 with no heat sink. With a heat sink, they can handle a lot more. But we don't want it to get hot. You could use about any N channel Mosfet, but do the math on the heat dissipation.

The gate drive resistors will drain about 1uA per volt of pack voltage, so not a big deal. As shown, a minimum of 24v is needed on the pack. For lower voltages, R1 would need to be reduced.

Reverse Polarity Protector.jpg (31.46 KiB) Viewed 114 times

[spinningmagnets]

Thanks AW and Fechter! I very much appreciate your help. Perhaps I will make these...and call them the "positive E-Fecht" (The name "Amber Wolf" is already being used for my line of long-bikes)

Amberwolf, Is there a re-settable breaker that could be used in place of a fuse? similar to the push-button on a GFCI? Though I believe shorting the battery can damage it, My main concern is a friend buying a set-up from me, and after modifying the connectors (backwards by accident) he ends up frying the controller.

[amberwolf]

You could use any breaker, but in my experieinces so far breakers take long enough to pop vs a fuse that you might blow up a BMS on some of these packs before the breaker pops. I guess if you size the breaker right it shouldn't be a problem, and there probably are faster-blow breakers, but the average cheap ones sure take a heck of a long time (sometimes several seconds of "normal" overcurrents; up to a second on a dead short).

As long as the diode is sized right to handle the current flowing thru it, and heatsinked, it'll handle the current flow as long as is needed and prevent the controller from being damaged. But it will be large and with a heatsink will add bulk to your setups. If it only needs to handle an instant of overcurrent, it can be a lot smaller and maybe not need any heatsink.


Fechter's is a better approach for a pass-thru protection than a diode in series would be. Mine is just copied from what I have read of others using here on ES, and is a brute-force protection. Also, with mine, if the diode fails before the fuse blows, it won't help the controller any. Two or more in parallel would mitigate that some, but it's still possible that a really high-current capable battery pack could source enough instantaneious current at a short to fry the diode(s) before a breaker pops (hopefully not before a fuse does, if the fuse is sized right).

[bandaro]

ok, i have more of a question than a request, if i was to use 12 lfp4 cells, hooked in series, could i have them permanently in series as well as having them in 4 sets of 3s for the charging? so basically could i balance charge as 4 sets of 3s while the pack is still connected (but no load) as a 12s pack? or will this destroy charger/cells/void balancing effect?

[fechter]

ok, i have more of a question than a request, if i was to use 12 lfp4 cells, hooked in series, could i have them permanently in series as well as having them in 4 sets of 3s for the charging? so basically could i balance charge as 4 sets of 3s while the pack is still connected (but no load) as a 12s pack? or will this destroy charger/cells/void balancing effect?

You can do this as long as the charger outputs are isolated. If the negative charger output is connected directly to the ground pin on the AC plug, it is not isolated and will short the pack when you plug in more than one (smoke, fire, etc.)

[bandaro]

hmmm, ok, sounds promising then, but i cant find anywhere that says either way for the charger i have, could i hook a multi meter up to it and find out that way? but use the neg wire as its dc input?


this is the charger: http://www.hobbycity.com/hobbycity/stor ... duct=11170

[amberwolf]

There are a few posts around describing how to use a meter to test for isolation in power supplies, but you may have to use Google to do a site search rather than the forum search.

[fechter]

hmmm, ok, sounds promising then, but i cant find anywhere that says either way for the charger i have, could i hook a multi meter up to it and find out that way? but use the neg wire as its dc input?


this is the charger: http://www.hobbycity.com/hobbycity/stor ... duct=11170

Sorry for the delay here.

The charger shown uses a power supply (not included). The power supply is the part that needs to be isolated. To test, use an ohmmeter from the ground pin on the AC plug of the power supply and measure to both output terminals. If you see a reading that is near zero (usually to the negative side), then the supply is NOT isolated. If it is isolated, the reading will usually be above 10k ohms or so. Most power supplies are isolated, but you just want to be sure.