hi all,
Likely a very basic question here. I'd like to use a variable dc power supply to charge a drill battery (the charger seems to be damaged and burnt out).
The battery and charger state that it's 14.4v, 0.3A. Std 5 ( which I found is a German rating of around 1800 mAh).

So if I set the power supply to current limiting (max) 0.3A and 14.4v, it seems to max out at 0.3A at only 0.2v! Long time since I did electronics, but this seems like a short circuit. Does this mean the batteries are fried/burnt out too? Do damaged batteries effectively become short circuited?

Any thought would be great. Sorry if it's a stupid question! Cheers

 

Be aware that when the charger is connected to the battery, you are not measuring the charger, you are measuring the battery. And yes, a 14.4V battery that measures 0.2 volts is in very bad condition. Your charger might be perfectly good but refusing to commit suicide by trying to charge a bad battery.

 

Your charger might be perfectly good but refusing to commit suicide by trying to charge a bad battery.

Or possibly it did commit suicide by trying to charge a defunct battery.
If you leave the battery connected at 0.3A does its voltage rise?

 

I did just that!
Sure that I would be down off the shed roof in time, I put my 14V drill battery on my power supply, as I had done many times before. But I got delayed!
There was this THUMP noise...


I didn't pull the battery apart, this is how I found it The insides of one cell was unwrapped some distance away.
Some pieces are still missing, lost in my shed!

Yes, you can try it for NiCad batteries, but keep an eye on the battery for heating and monitor the volts. Also, I'd be wary of doing this for some other battery chemistries.

 

AND... You must use a series diode.

 

hi all,
Likely a very basic question here. I'd like to use a variable dc power supply to charge a drill battery (the charger seems to be damaged and burnt out).
The battery and charger state that it's 14.4v, 0.3A. Std 5 ( which I found is a German rating of around 1800 mAh).

So if I set the power supply to current limiting (max) 0.3A and 14.4v, it seems to max out at 0.3A at only 0.2v! Long time since I did electronics, but this seems like a short circuit. Does this mean the batteries are fried/burnt out too? Do damaged batteries effectively become short circuited?

Any thought would be great. Sorry if it's a stupid question! Cheers

Ideally you need to know what type of battery it is, like Nicad, nimhi, lithium-ion etc, only then can you proceed to attempt to charge it back.

 

thanks all for the comments!

- the reason im using the variable power supply is that the original charger 'committed suicide'! it was half melted, I suppose due to the damaged batteries...

- I will try connecting it for a longer period to see if the voltage does increase, so far I only connected for a few seconds

- I will check what kind of battery it is, don't know off the top of my head and don't have it handy...

what is the significance of the series diode? what is it for and why is it essential?

thanks again. cheers

 

what is the significance of the series diode? what is it for and why is it essential?

YES. It prevents the battery from killing the power supply. I know the hard way.

 

Oh, I see. The power supply I'm using has a current limiting feature which I set to 0.3a, so I assume it wouldn't be able to kill the supply? I hope so since I paid a lot for it!

Just checked the battery and it's a ni-cd , so I'll try to connect to see if the voltage rises. Strange thing is that this drill has hardly been used, guess it's just a poor quality one...

 

Fair chance the original power pack melted down due to a failed battery that went into an internal short condition. It happens fairly often in really cheaply made cordless drill battery packs due to extremely cheap quality cells.

 

Fair chance the original power pack melted down due to a failed battery that went into an internal short condition. It happens fairly often in really cheaply made cordless drill battery packs due to extremely cheap quality cells.

AFAICT: the manufacturers deliberately make dodgy chargers that cook the battery so they can sell you a new drill for less than a replacement battery.

when both of my battery packs conk out - the drill will become slightly less cordless than when I bought it.

Its worth being resourceful as well as opportunist when price promotions crop up.

 

I opened up the battery pack and it was a bunch of cells in series. I might try to get good quality cells and replace these... any views if this is worth doing? (the drill isn't an amazing one after all...)

Also anyone have any thoughts on my question on the power supply? If it's current limiting, then safe and no chance of power supply 'suicide'?!

Cheers

 

NO!

Also anyone have any thoughts on my question on the power supply? If it's current limiting, then safe and no chance of power supply 'suicide'?!

See under battery backup (or another power supply)
https://blog.uk.tdk-lambda.com/uk/2...-external-diodes-be-used-with-a-power-supply/

I'm working on a supply that committed suicide. A 0-40 V, 0-3A supply I had one years ago that did as well.

The only type of supply that would not have this issue provided it was properly rated is an electronic load or a 4-quadrant power supply. These are capable of operating in +V,+I, -V-I, +V,-I and -V+I modes. They can source and sink current in both directions independent of the sign of V.

 

Hi,

Sub C NiCd batteries are easy to charge just apply a suitable current like 100ma to 200ma and wait about 24 hours maybe.

If you measure 0.2v across the battery pack then there may be an internal short between one of the welded jumpers and the side case of one of the cells. I say this because 0.2v is almost impossible to measure across a string of batteries in series unless they are ALL shorted. I guess this is possible but hard to believe. Normally a low voltage like that will jump right up to maybe 0.9v or more when you first apply 100ma. After that it will rise slowly, and that is for ONE cell. If you have several in series it should jump up more. I guess they can all be shorted, but i would check for a major short across one of the cells first. The only thing that prevents this kind of short sometimes is the plastic over wrap on the cell bodies. If it is worn on one cell it could cause this condition.

It's a little expensive to replace 10 cells. You can do it, but if you do you should get the cells with the welded tabs.

Consider also using a 12v lead acid battery. I got tired or replacing my cells in my drill so i switched to a 12v lead acid battery that is rated for more than 7 ampere hours, much above the silly sub C cells that are at most around 2 ampere hours. I used a heavy wire to run to the battery and use push on terminals so i can even switch to a new battery quickly.

 

I opened up the battery pack and it was a bunch of cells in series. I might try to get good quality cells and replace these... any views if this is worth doing? (the drill isn't an amazing one after all...)

Also anyone have any thoughts on my question on the power supply? If it's current limiting, then safe and no chance of power supply 'suicide'?!

Cheers

All the chargers I've opened so far were pretty much a current limiting resistor.

Over charged cell packs usually suffer one or more shorted cells - each shorted cell causes more stress on the remainder.

Its common for the resistor to burn out - the ones with thermal cut out tend to do better.

 

Over charged cell packs usually suffer one or more shorted cells - each shorted cell causes more stress on the remainder.

Over-discharging a NiCd battery pack causes shorted cells by reverse charging the weakest cell(s). If the drill doesn't have a low-voltage cutout and you run the drill until it barely turns then you risk getting shorted cells.

 

Over-discharging a NiCd battery pack causes shorted cells by reverse charging the weakest cell(s). If the drill doesn't have a low-voltage cutout and you run the drill until it barely turns then you risk getting shorted cells.

Probably higher risk of reverse charging the weakest cell on a drill, but my shaver works best if I run it down each time before recharging.

It came from Freegle and lasted less than 5min per charge - repeated charge/discharge cycles got the LCD time counter down to 0 before the motor gave up.

apparently the "memory effect" was first noticed in orbital spacecraft that exposed solar panels to the sun on a very regular schedule and never got fully discharged.

 

I "fixed" one of my drill batteries by throwing out all the cells and adding a long lead and a cigarette lighter plug. Now I have one drill that can work off the car. Also a power supply I have with a cigarette lighter socket.

 

I might try to get good quality cells and replace these... any views if this is worth doing? (the drill isn't an amazing one after all...)

I rebuild numerous battery packs for family and friends every year and these guys are where I go for premade rebuild kits. The quality of their cells are excellent.

http://gcbattery.com/power-tool-batteries/
Their 2.2 Ah packs are a huge step up in capacity and quality of the typical crap that's used in most everything now and as I have come to see since I started using them about 3 - 4 years ago their service life is excellent.

For the odd things or for applications where I want to go to a substantially higher cell capacity for less rebuilt pack investment I use the NiMh cells from here.

http://www.all-battery.com/index.aspx

I prefer their 3000 mAh cells for rebuilding things (best energy density for the money spent) since they are typically a good 2 -3X higher capacity than most OEM cells you will find.

Relating to how well the tool will work I can say for sure that in everything I have rebuilt the working power increase if easily noticed and I have rebuilt enough battery packs in the last 2 years to now have filled a 5 gallon bucket with the dead ones!

Especially if you are rebuilding a cheap pack that originally used~800 - 1000 mAh 4/5 sub C cells on a spacer plate to make them look like full sub C units (black and decker or terrible for that cheat) with full sized sub C 3000 mAh NiMH cells!

 

Oh, I see. The power supply I'm using has a current limiting feature which I set to 0.3a, so I assume it wouldn't be able to kill the supply? I hope so since I paid a lot for it!

Just checked the battery and it's a ni-cd , so I'll try to connect to see if the voltage rises. Strange thing is that this drill has hardly been used, guess it's just a poor quality one...

Good nicads are easily rechargeable from reverse or dead cells, you need a descent 3amp 3-5-V psu with short pulses of 1 to 2 minutes across the dead cells, watch for the cell getting warm, and then retest its single voltage with a voltmeter, it should pull back to 1.25v, do this with any dead cells, the put pack into the drill charger and monitoring each cell with a voltmeter, I've done this several times,


worst case is the cell is totally duff, snd has to be removed and replaced with fresh ones.