# ni-cad to li-ion battery conversion?



## skinee (25 Jan 2010)

ca


----------



## peter99 (27 Jan 2010)

It's usually the charger that's the problem so if the voltage is the same for the machine motor and you have the charger I would have thought so.


----------



## wobblycogs (27 Jan 2010)

As I understand it the over-discharge protection on Li-Ion is normally built into the cell under the casing. With tool batteries though it might be a separate part since the manufaturer wouldn't have expected you to open the outer plastic casing.

There are a couple more things to think about before you try a swap though. You will have to ensure that the voltage provided by you home made Li-Ion is about the same as the voltage supplied by the NiCad / NiMH. The maximum discharge rate of a Li-Ion is much much lower than a Ni-Cad so you will need more cells to compensate for this (e.g. if you take out 4 Ni-Cad you might need to put back 10 Li-Ion). Finally, you need to make sure that your newly created battery is within the charging limits of your charger and that it can correctly detect when the battery is full.


----------



## Racers (27 Jan 2010)

Hi,

This looks like a whole can of worms, I wouldn't attempt it, what with the different voltage of the cells (1.2V for a Nicad and 3.6V for Li-ion) and the over discharge protection you could end up with a battery that catches fire of explodes.

After you have figured everything out it would probbaly be cheaper and safer to buy a new drill.


Pete


----------



## RogerS (27 Jan 2010)

Also some of the chargers profess to be 'intelligent' so what they'd make of your Li-ion recell is anybodies guess! Might even think that the battery is fully charged and refuse to charge it.


----------



## ondablade (27 Jan 2010)

Barring somebody with a very high level of expertise was to take a look I'd agree it'd be far wiser to stay well away from this one, especially when you add in the stories one hears of fire and explosion risks caused by mishandling. 

My limited experience is with NiCads. On the systems i've seen the various monitoring functions are matched to the very specific charge/discharge characteristics of this type of cell. e.g. remaining charge is inferred from a very precise voltage reading, which voltage in turn is a reflection of the physics of the NiCad.

It sounds like LiIon cells are quite different...

ian


----------



## JohnBrown (27 Jan 2010)

I agree that you should not try this. Lithium cells require a different charging strategy, and multi-cell batteries usually have a cell balancing circuitry to prolong the life of the battery and prevent polarity reversal problems. Added to which, I don't think you'll find rechargeable Lithium cells with the same voltage as Ni Cad or Ni MH cells.

As far as charging is concerned, Ni Cad or Ni MH chargers detect end of charge by using either the change in voltage(or lack of it) over a period of time(deltaV) or the change in temperature of a period of time(deltaT), or a combination of both. Chargers will also use a maximum time, maximum terminal voltage or maximum temperature as failsafes. All of these are likely to be incompatible with Lithium cells.


----------



## skinee (27 Jan 2010)

ma


----------



## peter99 (27 Jan 2010)

from whats been posted above it seems a lot of work to me. 

I've just bought an 18v metabo drill/driver. It's nicad. its the exact same drill (excellent) as the new lithium model. lithium price £330, nicad price £149, end of range.

Aah I hear you say, all those nicad battery problems. Well it came with a 10 minute conditioning charger (you can leave them in it if you wish so always ready to work) and if flat then only 10 mins - and it does work i've tried them.

it means batteries will charge around 3000 times instead of normal rubbish.

it has a three year warranty on everything including the batteries and charger.

But some won't touch it because its nicad.

Peter


----------



## Racers (27 Jan 2010)

Hi,

If you replace the cells with Li-ion cells how are you going to cope with the voltage difference? it will 3 times the voltage if you do that.

I think the problems outweigh the benefits by a substantial margin.


Pete


----------



## ondablade (27 Jan 2010)

As Peter i'd have to say that i also took advantage of the very good deals going on the now 'passe' NiCad drill drivers. D&M had (and probably still have) the very nice 18V Bosch blue/industrial model on offer a few months ago in a deal which included three battery packs in a plastic case for about £135.

The battery is a bit bulkier and hasn't quite the performance of the LiIon, but on the other hand there's no significant difference i could see to the mechanicals. My previous 1998 14V green Bosch is meanwhile still going strong.

I can't imagine where in my type of occasional usage a LiIon battery could make any very significant difference to me.

It made it very hard for me to see the point in ponying up another almost £300 for the latest and greatest.....

ian


----------



## JohnBrown (27 Jan 2010)

skinee":25lothe2 said:


> many thanks for all your replies,my main reason for wanting to try this is the outrageous price of power tool batteries in general and li-ion in particular also the overwhelming benefits of the li-ion,my AEG charger will charge all three types of battery therefore it seems to me that if i can remove the nicads and replace them with the exact same cells that are in a li-ion battery(i have li-ion batteries for comparison)then the only other possible problem could be an absence of the over discharge circut,i will consult a person i know who is an eletronics expert for his advice(he may be able to build the circut for me)if the batteries can be converted i will post the information here.


Well I may not be an "electronics expert", but I have written the firmware, including battery management for several products which are "out there" in numbers that exceed 100,000, and I would not want to do what you are contemplating. Lithium cells are not only way less tolerant of charging voltage variations, but are also much more dangerous when they fail.

Added to which, although Lithium gives between 2 - 3 times more energy per charge, NiCads can be recharged between 3 - 5 times more in their lifetime.
I personally think that the main advantage of Lithium batteries accrues to the manufacturers, who are able to sell replacement power tools to those who lust after the latest technology!


----------



## peter99 (27 Jan 2010)

exactly that Ian. Brilliant products, just out of fashion even though the same machine.

John, you hit it on the head. And more so the reason manufacturers want you buy cordless is they make more money on the 2nd set of batteries (and the third).

I posted on another thread the true cost of cordless. if you want to get 5 years out of a frequently used product ypu have to factor in replacement batteries. I have a Hitachi impact driver. 3ah nimi bateries. £220. batteries now need replacement after 3 years. hitachi = £90 per battery. True cost = £400 for 5 to 6 years use. new price with same product £230. So reality is it has a life cycle of 3 years or £100 a year whether you throw it away and replace when batteries done or replace batteries.

So because I use a lot of powertools in my job we've gone back to corded where possible and are saving a fortune. Only using cordless where it really is easier. We even didn't renew the 24v sds cordless, just bought a really good quality corded at one third of the price. it'll last 3 times as long so probably works out at something like 10% of the cordless price over the term.

call me cynical but I saw on a large stand in screwfix 3 weeks ago a Bosch professional 18v drill driver, 3 lithium batteries and charger, half price, £160 ish. Sounded brill.

So I looked closer. 3 x 1.3 amp batteries. this means recharging 2 to 3 times for every 2.5 to 3 amp hour battery. So the battery charger (i hour non conditioning) would be constantly in use when used heavily. The batteries don't last as long as nicad etc so Bosch has you re buying a drill or set of batteries in next to no time, and probably a charger as well. People were grabbing them like no tomorrow.

Think there's still one or two genuine bargains around though!

Peter


----------



## Mike Wingate (27 Jan 2010)

My Bosch battery replacement was going to be £70+. So I bought a new drill from Axminster White brand with 3 batteries for the same price. Not as nice a feel or as well made, but the drill is still going and is compatable with the 18v Aldi stuff.


----------



## mailee (27 Jan 2010)

I am still using one of my Makita Ni Cad batteries that came with my drill/driver.......Fifteen years later! Don't make em like they used to. :wink:


----------

