Emergency "Bad Boy" ultra Compact charger

[NeilP]

Well warning or not it is ducking fangerous !


I was playing with it for the reasons above, to give quick totally monitored boost of low pack ONLY. Would not consider use with cells much above 3.5/cell.


I have found that a starting cap just does not have what it takes for use over 2-3minutes before it craps itself and let's out all its magic smoke. Guess how I know.
For this to work you would need caps designed for continuous run use, but then the cost of them becomes and issue. You are suddenly in to $150 a time instead of $5

I

 

[Punx0r]

Sorry, didn't mean to come across as a busy-body, just wanted to ensure we're all on the same page. I'm happy to work on 240V mains wiring, but caps and rectifiers at that voltage give me the heebie jeebies.

I would definitely have a rapid bleed resistor on the cap and always connect/disconnect the mains and battery so you're never touching the battery connector with the mains connected. The bleed resistor ought to be able to discharge the cap in the few seconds between mains disconnection and battery disconnection.

Are motor run capacitors suitable for your needs? IIRC from replacing the caps on a motor a few weeks ago the start cap is electrolytic and the run cap a film type. AFAIK the start cap only stays in circuit until the motor reaches approximately half speed. So very low duty.

Luke's suggestion of an inductor to improve the power factor should work, although I believe the amount of inductance required will vary with the load, so you'd be shooting for an average. I'm having a brain fart about how to calculate the PF, but the most reliable way is simply measuring the ratio of real and apparent power, which should just require current and voltage measurements before the cap and into the load. I'm not sure whether the load should be measured before or after the rectifier, but I'd guess before as the rectifier is a non-linear load, which cannot be corrected by adding inductance.

Or avoid the hassle and just tolerate the crappy PF

Stay safe!

 

[fechter]

For this to work you would need caps designed for continuous run use, but then the cost of them becomes and issue. You are suddenly in to $150 a time instead of $5

I

Check the surplus places. Here's one:
http://www.surpluscenter.com/Electrical/Capacitors/Motor-Run-Capacitors/?page_no=1&page_length=9999

Cheap enough there.

I think you could just put a big 10K resistor across the cap as a bleeder. It will bleed off in less than a minute. With an AC cap, there's a random chance it may be zero when you unplug it, depending on where you are in the cycle. If you're really paranoid, you could rig a relay that opens the bleeder circuit during charge, and use a much lower resistance for the bleeder resistor so it discharges in a second after unplugging.

The current you get will be a function of the capacatance, the line frequency, and the voltage difference between the line and the pack. I'm sure there's a formula for it somewhere. Normally the voltage difference between the pack and line will decrease slightly as the pack charges, but for lower voltage packs the current will be essentially constant.

 

[zombiess]

Its probably against the spirit of this super dangerous power supply, but why not add in a simple voltage monitoring circuit so a cut off level can be set and a relay opened breaking the mains connection? While not safe, this would add some protection.

Op amps and relays aren't that expensive or heavy.

 

[heathyoung]

Fechter came up with this the last time this charger design was discussed.

If you short the output of this circuit - you get 0v and no fireworks. Have a think about this - this is why low IR packs have low current. A zero IR pack will never charge on this circuit.

Capacitive reactance (ie. resistance) is dictated by frequency and capacitance. Have a think of this circuit as two series resistors.

Think of the voltage across the lower resistance resistor. That's the voltage that is going to appear across your pack.

 

[fechter]

I don't think the IR of the pack will change things much (unless it's way high). The current is what the pack cares about, so if you get a certain current, the pack will charge at that rate regardless of it's internal resistance. The voltage differential between the pack and the line will matter.

I designed a super crude cutoff circuit you could dial in for a 'safe' voltage for the pack and it would cut the AC input when the limit was reached using a solid state relay. If you forgot to babysit during charge, the current should drop to zero when the voltage limit is reached and nothing burns up. See: http://endless-sphere.com/forums/viewtopic.php?f=14&t=36646&start=25

There's a whole other thread on basically the same concept.

 

[liveforphysics]

I am interested in making some high power versions for my 2014 SR (28s 75Ah) and the Palatov (84s 75Ah NCM) that is as tiny and light as possible while still being able to max out a J1772.

 

[NeilP]

I am living in the woods at bottom of farm for 5 days, just solar panal and iPhone signal to post this, so not a long one.c

Motor start caps I have are all in plastic case with built in discharge resistor.
Thanks for surplus supply link, will look when home.

Current/pack voltage monitoring would be totally manual unless it can protect against massive over voltage to mains voltage. I'd likely fit a charge point, wired via controller shunt, and leave it powered on, and view charge via the CA. Yes risky if anything were to die short circuit and feed rectified mains direct to the controller, so if your circuit is fast enough to shut it down in that event, then maybe it would be good

 

[riba2233]

Looks like someone is selling similar charger...

http://e-volks.com/capacith_charger.html

 

[Punx0r]

Based on that webpage I wouldn't ever buy anything from that guy...