Hi Roland, I do love your wonderfully practical take on things - when are you going to write a book?
Anyway, from my rudimentary understanding of these things, 180V / 200A = 0.9 ohms of resistance in your welding rods. 200A x 200A x 0.9 ohms = 36kW of heat from your resistor. That sounds horribly wasteful if you are doing it for any significant amount of time... Care to comment on that? On 20 Apr 2014, at 19:39, Roland wrote: > You also have to be careful not connect standard battery jumper cables. This > will cause a arc and could blow up your batteries if there is any hydrogen > gas and or poor connection. > > I use a battery load bank which I built for battery load testing and can also > be used as a resistance to prevent the current surge. > > The components consist of a steel equipment box, a 1/2 inch thick insulator > board I pick up from a motor shop. Two box lug terminal strips rated for 500 > amp that is mounted on the insulator board. A 500 DC contactor rated for the > battery voltage with a coil rated at 12 vdc. A momentary switch to control > the contactor coil which is normally use for a single battery testing. > > A maintain switch for a longer on time of the contactor. A volt and amp > meter rated for the battery you are using. > > The resistance is made from a high temperature stainless steel welding wires > which is about 1/8 inch or 0.125 inch in diameter and 36 inches long. They > are loop back and forth with the ends connected to the two terminal strips > place about 10 inches apart. You can add more wires in series to limit your > ampere. I limit my ampere to about 200 amps using 10 wires in series for a > battery pack rated at 180 volts at 250 ah. The welding wires are rated for > over 1000 degrees F. > > I used one wire to load test a 6 volt battery and two wires in series for a > 12 volt battery for a 200 amp load. > > Drill a series of 1/2 inch vent holes on the top of the box and on the back > of the box for ventilation. > > Used two brass motor terminals which is normally used on DC motors that I got > from the motor shop. I only connected the positive voltage through this load > bank and the negative voltage connects directly from battery to battery. > > You can also use a Power Anderson 300 to 400 amp receptacle on the vehicle to > connect this device which is more safe. > > Roland > ----- Original Message ----- > From: Lee Hart<mailto:[email protected]> > To: Electric Vehicle Discussion List<mailto:[email protected]> > Sent: Sunday, April 20, 2014 11:37 AM > Subject: Re: [EVDL] Charging Batteries from Batteries? > > > Dan Baker wrote: >> I have question around charging the battery pack on an EV from a larger >> pack of batteries, same voltage. > > Think about what happens if you connect two buckets of water with a > siphon hose. Water flows from the higher one to the lower one, until > they are both at the same level. No pump is needed! If the water level > is quite a bit different, the initial rate of flow is quite high. But as > they near the same level, the amount of water that transfers gets lower > and lower. Depending on how big and how long your siphon hose is, it can > take a very long time for them to finally reach the same level. > > Lead-acid batteries behave the same way when connected directly in > parallel. If both batteries are the same nominal voltage, current flows > from the more-charged one to the less-charged one, until they are both > at the same voltage and same state of charge. For instance, connect two > same-capacity batteries in parallel. One is fully charged, and one is > dead. They both end up at 50% state of charge. > > If you connect them with big thick low-resistance wires, the initial > current can be very large! The peak is roughly the amphour capacity of > the biggest battery (i.e. 100 amps if it's a 100ah battery). > > But it quickly falls to a low level, as the current makes the > higher-voltage battery drop, and the lower-voltage battery rises. It > takes a day or more for them to fully equalize to the same state of charge. > > You can limit the current with resistance in the wires. Deliberately > using smaller or longer wires, for example. The voltage difference > between the batteries is quite small, so it doesn't take much resistance. > > If you're in a hurry, then your "source" pack can be a little higher > voltage (no more than 10% higher than the "destination" pack). The > current flow will be even larger, and stay higher longer. You have to > monitor the current and time it carefully, so the lower-voltage pack > won't get overcharged. This is called "dump charging". Done right, it's > about the fastest way to charge batteries. Done wrong, it's one of the > best ways to destroy batteries! > > Charging this way is very efficient. The only losses are the inevitable > efficiency losses in the batteries themselves. The wire between them is > essentially lossless. > >> My questions for the list: how do I transfer the charge from the solar >> bank to the EV pack? Can I just use a charge cable directly and the two >> banks will equalize? > > Yes. If they are the same nominal voltage, this is safe. You can leave > the cable connected as long as you like. Just be aware that the peak > current when first connected can be very high. > >> Or would I need to use a charge controller? > > You can. In fact, *some* kind of charge control is necessary when the > charging source is more than 10% above the battery's voltage. > > The charge controller will inevitably lower your efficiency a bit. > >> a 45 amp solar controller I could hook from the main battery pack to >> the EV pack but I fear the input amps would exceed it? > > If this is a charge controller designed for PV cells to a battery, don't > use it with a battery (or other low-resistance) power source on its > input. It's intended to be powered by PV panels, which are a *current* > source. They can be safely shorted to reduce output. But you can't short > a battery or power supply! > > -- > If you're not stubborn, you'll give up on experiments too soon. > And if you're not flexible, you'll pound your head against the wall > and you won't see a different solution to a problem you're trying > to solve. -- Jeff Bezos > -- > Lee Hart's EV projects are at > http://www.sunrise-ev.com/LeesEVs.htm<http://www.sunrise-ev.com/LeesEVs.htm> > _______________________________________________ > UNSUBSCRIBE: > http://www.evdl.org/help/index.html#usub<http://www.evdl.org/help/index.html#usub> > > http://lists.evdl.org/listinfo.cgi/ev-evdl.org<http://lists.evdl.org/listinfo.cgi/ev-evdl.org> > For EV drag racing discussion, please use NEDRA > (http://groups.yahoo.com/group/NEDRA<http://groups.yahoo.com/group/NEDRA>) > > -------------- next part -------------- > An HTML attachment was scrubbed... > URL: > <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20140420/a436da08/attachment.htm> > _______________________________________________ > UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub > http://lists.evdl.org/listinfo.cgi/ev-evdl.org > For EV drag racing discussion, please use NEDRA > (http://groups.yahoo.com/group/NEDRA) > _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
