Battery discharger

[daniel hallman]

I've seen some of the battery dischargers that use what appear to be several 12 vdc tail light lamps hooked up on a parallel circuit. My question is why could'nt you just buy a 50 watt/12vdc lamp like you would use on a R.V. ,wire up a lamp socket to fit the battery and just plug the battery in when it needs discharging?? Would this discharge the battery to fast? I'm building a battery cooling box out of a thick styrofoam container and have a 3 inch 12vdc fan and a 3 inch 120vac fan to mount in the end of the cooling box. It also has an elevated battery rack so that I can put a couple of freezer-packs under the batteries (I work in a laboratory and we've got loads of these freezer packs since most of our materials have to stay cold in transit). But anyway the main deal is the battery discharger. If this is'nt a good way to do this I'm open to any and all sugggestions. THANKS, THE LAB RAT...:cool: :confused: :confused: :confused: :cool:

[RickE]

I'd go ahead and try your idea,but the first time you discharge a pack keep close tabs on the wires, connector, etc., for any signs of excessive heat. Heat is the biggest killer of these packs and their componets, and if no signs of high tempertures show-up, you've got your discharger!

Hope this helps,
RickE

[daniel hallman]

Talked to the guy that runs the "hobby shop"about this, told me that it would cook the batteries by discharging them way to fast . Well that was just a minor problem to overcome, just went to the local U-Pull It car salvage place and picked up one of the rotary style dash light dimmers, wired it up in series with the 12vdc lamp. Now I've got a discharger with a variable rate that I can monitor with my digital voltmeter ( beats picking one up to find out that it was really to hot to pick up in the first place). Thought about heading to the patent office with this one, Total cost was about two bucks, about 1.50 for the 12vdc lamp at the local Wally World and a whole fifty cents for the switch. :cool: :cool: :cool:

[forresterace]

Daniel
Actually your idea of using a 50 watt RV bulb would work OK except that it would only draw about 4 amps from 12 cells (watts = volts X amps or 50 divided by 12). Generally the idea in discharging nicads after a race is to discharge them at a similar rate as was used in your vehicle. The average car tail light bulb ( #1152 if I remember correctly) will draw about 2 amps apiece. If you wire ten bulbs in parallel, the current would be about twenty amps. These ratings would apply to 12 volts and would change if used for lower voltage packs such as six cells (6 V.) The actual discharge current isn't critical, but most racers use 6-10 bulbs in parallel. The reason lightbulbs are commonly used rather than resisters is that they dissipate the heat generated harmlessly, are relatively inexpensive and last a long time.
The most effective battery pack cooling device is very easy to build. All it takes is a 6-7" length of 4' diameter ABS drainpipe with a 3" computer fan (12V.) mounted in one end. The nicad pack(s) are then inserted in the open end of the ABS pipe and let sit there until they are cooled. It is a very efficient device and can also be used to sit over top of your motor to cool it. This design is commonly used by boat racers and airplane flyers all over the world.

Doug Forrester
Forresterace Designs

[NITROMETH]

Thanks for the input, guess that I'll play it safe and go with the tail light set up. I've got the stuff for the cooling box, just need the time to put it together now. Daniel , A.K.A. THE LAB RAT...:cool: :cool: :cool:

[NITROMETH]

Thanks for the input, guess that I'll play it safe and go with the tail light set up. I've got the stuff for the cooling box, just need the time to put it together now. Daniel , A.K.A. THE LAB RAT...:cool: :cool: :cool:

[Andrewg]

Daniel you can use the headlight

but what is most important is not to discharge below .9 v per cell and despite all the crap that is put out - lower discharge rates are better for your cells - particularly as you get down to low voltages

You can generally get a handle on this by measuring the packs with a multimeter as they discharge. I use a set of tailights which are set up so that when the filament stops glowing a 6 cell pack is at .9v. Do this by varying the number of globes. 6 will be close

Andrew
www. fastelectrics.com