drill batteries.

[ukracer]

I had a bright idea about buying a cheap 18 volt lithium battery and gutting the cells for my old makitas.

So far so good. But when I take the new one apart it has electronics in it and only only 5 cells which is weird in an 18 volt drill.

Any suggestions?

 

[Maker]

What's wrong with 5 cells? Lithium ion cells are 3.7 volts, 5 x 3.7 = 18.5v (up to 4.2 when fully charged) I think the electronics will likely be balance circuitry for charging, you'll need to put these into your modified batteries.

 

[ukracer]

Ah 3.7 that good as they are blank. makes sense. I an going to charge with my rc battery charger as the charger for the old batters is a nicad charger. So I don't see why I need charge circuitry. ..

 

[hotrodder]

Isn't the circuitry is to stop them catching fire or even exploding due to excessive charging rates or overcharging or both or something along those lines? Remember the laptop catching fire stories that made the news a few years back?

 

[Maker]

Remember the laptop stories that made the news a few back?

Or the EE power bars right now.

So I don't see why I need charge circuitry. ..

A Li-ion pack has it's normal + & - wires, as well as smaller wires going from each cell to the charger so it can moniter the voltage of each cell to prevent one cell from reaching a different voltage, then getting charged overly quickly by the other cells which would make it explode. The internal circuitry in the battery covers this, you'll need to break out these wires to the new charger.

 

[ukracer]

So in that case I can just replace the cells as they are in the nicad case and use the nicad charger if it's got charger circuitry in the lions

 

[Maker]

I think so...

 

[hotrodder]

So in that case I can just replace the cells as they are in the nicad case and use the nicad charger if it's got charger circuitry in the lions

Dunno. The charger for my Hitachi cordless stuff goes about it's business differently to the way Nicad chargers do as deep cycling Nicads is good for them (memory effect) but bad for Li ion/can shorten their life. Instead of the slow drop in performance as the battery runs down the drill or whatever will just cut out (with no warning) at a certain point. Put the battery on charge and the charger first discharges it some more/'conditions it' before charging or something along those lines. As well as the usual + and - terminals on the battery case there are also 4 other terminals (T, Ls, LE, L+) that presumably help facilitate monitoring this and that

 

[Maker]

the charger first discharges it some more

I that case, I'd say you probably can't use your old charger with the Li-ion battery circuitry.

 

[hotrodder]

I certainly wouldn't but don't know much about it. I've got a vague recollection that nicads often get fairly warm when charging. The Li ion Hitachi batteries don't, i'm guessing that's on purpose as it's a good way to start a fire?

ETA http://www.buchmann.ca/article18-page1.asp and http://www.профсервис58.рф/HITACHI_model/Uc18yfl.pdf

 

[PhillipM]

You might find the NiCad charger won't cut off with the Li-ions as there's not the same voltage characteristics when they peak, or the same self drain through the cell resistance. You don't want to find out the hard way that the charger hasn't switched off when your battery pack is burning a hole through the remains of your house.

 

[GKQ]

You cannot use Ni-cad chargers on Li-ion batteries, it is very dangerous, over heating and explosions are common ( try a nicad charger on a li-ion R/C battery, have experience on this one ).
Ni-Cad batteries are charged constant VOLTAGE, Li-ion are charged with constant CURRENT ( although the onboard electronics does reduce this at the end of the charge to a mainatance level )
There are special chargers that can tell the difference and charge both, e.g. my new Hitachi Li-Ion charger can do both, but my old Hitachi Ni-cad can't. As some have pointed out nicads charge as a pack so 1.2V x number of cells. Li-ion charge individually, hence the electronics in the battery pack( it is a small computer that regulates/monitors everything, voltage, current, cell voltage taps, etc ), which also balances the charge going to each of the cells, hence the reason Li-ion batteries also charge much faster. With Ni-cads the whole pack has to wait for the slowest cell, hence variable current charging.
Graham

edit very important : Forgot to say Lithium burns white hot and is very hard to put out, DONOT use water, must be powder extinguisher.

 

[rtbcomp]

.........
Ni-Cad batteries are charged constant VOLTAGE, Li-ion are charged with constant CURRENT.........

When I was a lad NiCads were charged with a constant current. Lead Acid with constant voltage.

 

[rtbcomp]

http://www.theregister.co.uk/2015/08/05/ee_recalls_power_bar_after_fire_incident/

 

[GKQ]

Ref charging NiCads
"NiCad and NiMH batteries are amongst the hardest batteries to charge. Whereas with lithium ion and lead acid batteries you can control overcharge by just setting a maximum charge voltage, the nickel based batteries don't have a "float charge" voltage. So the charging is based on forcing current through the battery. The voltage to do this is not fixed in stone like it is for the other batteries." Link http://www.powerstream.com/NiCd.htm.
Graham