Replacing a Ni-Mh battery to AC input?

[hermtm2]

Replacing a Ni-Mh battery to AC input?

Hello,

I have a cordless drill which use a 14.4v Mi-MH batter source. The battery does not work anymore. It will costs me $150. Here is my question. Is it possible to replace the power source from the battery to AC adaptor. I mean as a DIY. I have done many DIYs but not with electricity since I am in Electrical Engineering problem.

The school teach me a lot of knowledge which I don't know when I can actually apply to. I would like to have this one as the first project.

Please help me what I need...

Thanks.

 

[negitron]

You could, if you can find a 14.4 VDC power source capable of sourcing however many amps the drill requires under load. You'd be better off trying to rebuild the battery pack, though. If you can get it open (some are fastened with screws, some are snap-together and others are glued or welded together) you will usually find they are constructed from standard cells, usually sub-C size. Just get new cells of the required number and type and a mAh capacity at least as large as the originals and connect them in the same configuration. If you had to cut the pack case to open it, just glue it back together with epoxy. I've rebuilt a few packs this way; the cells are MUCH cheaper than a new pack.

Also what drill is this? $150 is quite steep, even for a high-end Makita or DeWalt.

 

[hermtm2]

I have a Makita 6223d. It is a set with a work light which use the same battery pack. I need 2 of them. Each one of the battery is $75. Anyway I will try~.

Thanks.

 

[negitron]

There are also many places which will rebuild packs for you:

http://www.primecell.com/pctools.htm

Personally, I'm a DIY kind of guy but if don't think you can do it, the price is certainly right. Or at least better.

 

[vk6kro]

Cordless drills draw a lot of current, especially when you are working them hard.
Also, if you power them from the mains power, they are not cordless any more.

So, that would be difficult, but not impossible.

A better solution is to make up a battery pack and attach it to the drill with a short cable.
You would need to get a 12 volt battery from somewhere (like a motor cycle battery) and put it in a box that has a handle on it so you could carry it easily.
You can used the old battery holder as a connector to the drill. Just remove the old batteries and attach the cable to where the batteries used to connect.

You could also get about 10 NiMH (Nickel Metal Hydride) D cells and connect them in series to give you a 12 volt supply. You can get holders for these batteries at electronic stores, but not for 10 at a time. You might need 5 holders with 2 batteries in each.

You would have to arrange a charger, too. This should be one that detects when the battery is fully charged and stops the charging.

Before starting this, get a price on a new drill. It may be cheaper than making up a new battery pack.

 

[waht]

Basically under heavy torque the current can peak above 20 amps. So unless you can find a suitable switching power supply, the simplest solution it to rebuild the battery pack.

 

[hermtm2]

huh...

Rebuild not a DIY...

Thanks.

 

[vk6kro]

I've tried that a few times and it always works out cheaper to get a new drill.

Also, they seem to put them together with strips of stainless steel joining the batteries so you have to silver solder them. Did you find that?

 

[hermtm2]

I just sas the video on Youtube.

 

[hermtm2]

I can't even find how to disassemble the battery pack. I would like to see inside before it goes to gabage can.

 

[negitron]

Probably sealed. You've got nothing to lose by carefully cutting it open along the seam, since it's dead anyway. But first, look under any labels, since manufacturers like to hide screws there.

 

[hermtm2]

There was not the hide one. Also it seals completely.

 

[negitron]

Time to break out the hot knife.

 

[vk6kro]

Look for hot glue, too. A hot air gun will melt that OK.

If all else fails, my angle grinder will make short work of most things. Putting it back together afterwards is the hard part.

Even a bit of red-hot nichrome wire will slice neatly through plastic.