Over the Easter weekend, I got in a conversation with my son-in-law concerning his use of NiCad batteries when younger on R/C cars. He said he had a series of lights that they would use to pull batteries all the way down after a race to get them ready for the next race. Just recently getting rid of some NiCads that had developed memory and I got some more that I have a concern with, I was thinking of building one of these discharge light trees. Looking through a marine catalog for light sockets, yes I do stuff like that at work, I came upon a page of inverters. Wondering if a 12 volt inverter could be used to pull a set of 14.4 batteries down for recharging? Any opinions?
Ric
No idea of using an inverter. I use my old RC car discharger for doing this. There are lots of plans online for them, too. Here’s a good set of plans.
http://www.rccaraction.com/articles/htBuildDischarger_1.asp
should be able to make that for short money…
Though, if you have memory problems (battery, not neural), you might want to discharge the individual cells.
A sure fire way of discharging is to put the battery or batteries in a torch and leave it switched on . 24 hours should leave the battery exhausted—safely .
Mike
Bob and Mike,
Thanks for the replies. I had an idea of how to build the discharging tree, but appreciate the plans. As I said, I just got looking and found this inverter and next to it an inverter/spare power supply for a laptop and then a combination. Always looking for a new gadget and the idea of the inverter just started taking up brain waves.
Ah!!!
Sorry , Ric , I did not mean to put you off .
I admire tinkerers , they come up with good and useful ideas .
Yes , your devices would certainly power up a device to load and monitor batteries of many voltage values to ascertain total safe discharge–which , to those who are not aware , is a good way of prolonging battery life overall . I seem to remember Dave and Tony talking about how to look after batteries , useful info for those who are battery inclined . Like me with some of my stuff .
Mike
Spoke to Dave yesterday afternoon. He felt the failure of the idea may be that it would take the NiCads down too far and allow reverse charging. Even Bob’s design for R/C Cars says to pull off just as soon as bulbs dim. Dave gave me some instructions that follow Tony’s thoughts on trying to revive a set of batteries with memory. I may have not tried to that with a dedicated line of record keeping of charging results. Amongst many things to do and work on. 
I’m still intrigued about an inverter hooked to a 12 volt auto electrical systems with vehicle running powering a Maha battery charger to charge 14.4 volts NiCad batteries using the 110 volt converter. Maha charger plugged in to 12 volt system gives and error code of not enough input voltage to charge a 7.2 battery pack. If you here of a van burning on the way to Canada with a mysterious electrical fire, it could be us.
Needing to fully discharge rechargeable batteries before recharging is an old wives tale. There are some components in that process that can help a damaged pack, but it’s a very poor way to do it. Since is sort of works, the myth continues.
Draining a nicad very low will encourage the cell to reverse polarity, then when you charge it, it’s like a dead short. Very bad idea.
Get a good charger and your troubles will be over. The RC guys want to charge in the least time, and they compromise battery life. Are you sure you want to emulate that?
I carry a small 12v to AC inverter in my cars at all times. For one thing, I don’t have to buy a second charging cable for every electronic gadget, and in the case of my Maha, it makes it able to charge at full voltage. Be sure you get an inverter that puts out enough current. Look at your Maha AC supply, see how much current it draws (at 110v), multiply it by 110 (rough conversion) and make sure that number is less than the wattage of your inverter.
Regards, Greg
Greg,
Dave convinced me yesterday not to fully discharge the batteries because of sacrificing battery life.
Being electrically illiterate or at least a slow learner, I’m not 100% certain of what you are saying with the statement -
“Be sure you get an inverter that puts out enough current. Look at your Maha AC supply, see how much current it draws (at 110v), multiply it by 110 (rough conversion) and make sure that number is less than the wattage of your inverter.”
Specifications on charger states -
Rapid charge current: 800 mAh +/- 50 mA for NiMH & NiCD
400 mAh max for LIthium Ion
Tricle Charge Current: 70mA
Discharge Current: 300mA +/- 50mA
Safety Timer: 13 hours
Included adapter: Switching adapter 80V-240VAC autoswitch to 24VDC 0.83A
Capacity Accuracy: +/- 5%
Voltage Accuracy: +/- 0.3V
With that info, are you saying the inverter needs to produce 83 amps?
Since the inverter is supplying power to the “power cube”, you want the power cube’s power requirements at 110v.
Your specs sort of say .83 amps, but it’s not clear if that is at 110v or 240v.
So we can make a good guess at the input requirements by checking the output, assuming zero loss, and then adding some fudge factor.
It appears that the power supply outputs about 800 ma at 24v or thereabouts.
Assuming zero loss, that would be 80 ma at 240v volts (ten times the voltage would divide the current by 10 times.
This would be about 160 ma at 110, the output of your inverter that the power cube is plugged into.
So, the inverter would need to put out about 1600 ma at 11 volts dc, or 1.6 amps.
so fudge it up to 2 amps. In DC power in watts is volts times amps, so 12 volts times 2 amps is 24 watts.
Most car inverters are way over this, like 60 watts or more.
So get a car inverter that is more than 24 watts, and you will be fine.
I use a 60 watt inverter, no problems, and I can run a couple of 110v chargers from it.
Where you get big current, is something like a laptop, laptop power supplies can run over 4 amps at 19 volts, so that can be over 70 watts, so a 100 watt or larger inverter is required to charge newer laptops in a car.
Regards, Greg
Thanks, Greg. I read through what you wrote and shook my head in agreement, not understanding anything of what you were saying until the last statement. The inverter I’m looking at is designed to provide power for a laptop, so I feel it should cover my needs.