Worx H3

[The Medway Handyman]

Been looking for a cordless SDS for a while. Wanted a lighter 'drill shape' one, rather than the heavy square type IYSWIM.

I put up loads & loads of curtain poles & blinds. I've got a superb Makita mains SDS, but its big & bulky & even the very long lead never quite reaches a power point. Plus it gets grubby.

Picked up one of these today for £90.

a very light, 12v Li Ion cordless SDS that can be used as an SDS or a drill driver. The answer to a maidens prayer for curtain pole fixing.

It's got a standard SDS chuck with a max hole in concrete spec of 10mm - more than enough for the job and comes with an SDS/keyless chuck adaptor and a 6mm bit holder/SDS adaptor.

Not incredibly powerful at around 1 j - compared to the 2.5j on the Makita - but should be good enough for lightweight jobs.

Only thing that bothers me is the charger. The battery has a low charge cut out according to the instructions, so it can't really be over discharged, but the charger looks a bit flakey.

Its a wall wart with a lead going to a 'base station' that the battery sits in. It has a red LED for charging & a green for charged. Spoke to the 'technical dept' at Worx who 'think' it switches off when the battery is charged. I'm not convinced :-)

Haven't tried it in anger yet, I'll report back.

[John Rumm]

Of its Li Ion, then it must do... with NiMh etc a crap charger just results in short battery life. With Li Ion or Poly, a crap charger results in an incendiary device!

[Grimly Curmudgeon]

of hole drilling in concrete. For example; my ancient 12V Bosch SDS, when new-ish, would drill ~6 x

12mm holes in concrete to 3" deep per charge, battery being 1.3Ah NiCad. So that's a total of 18" of 12mm SDS. I recall the 12mm size as being relevant because at the time I was using that size of Rawlbolt quite extensively. Its replacement (Makita pattern) battery easily does that, but that's a nominal 2Ah, so no surprise there.

[The Medway Handyman]

Interesting! Could you elaborate Mr R?

[Dave Liquorice]

*Very* simply the chemistry of a Li battery has a lot of available oxygen. If a Li battery catches fire you can't put it out by excluding air as it has it's own supply of oxygen. Similary you can't remove the fuel. That leaves removing the heat but as it's effectively an exothermic chemical reaction that isn't easy...

[John Rumm]

and lithium and water is not a good combination either ;-)

[The Natural Philosopher]

There is no lithium metal in lithium batteries.

It is usually lithium carbonate IIRC. The fire risk is on account of the weird witches brew electrolytes which are highly flammable and produce as you say oxygen.

[John Rumm]

Yup, basically the level of control required in a charger for a lithium batter is much more sophisticated (hence why all the tools needed to switch to new chargers and incompatible mounts).

The batteries can get into a state of thermal runaway. That can cause the cells to vent a combustible electrolyte. So the best option is not allow them to overheat in the first place. Hence there is logic usually built into each battery that will try to detect fault conditions and prevent charging or discharge abuse from continuing. (sometimes this can be a bit over cautious and end up permanently "locking out" good batteries).

So the really cheap crude chargers that were an option on some NiCd tools are non starters on Lithium cells.

If they do burn then extinguishing them *and* controlling the temperature is vital. So if using water to extinguish for example - make sure you have plenty available to not only knock down the flames in the first place, but also keep playing on the pack to cool it after.

Things like fire blankets / sand etc just tend to insulate the thing and guarantee that all the cells will go up.

Have a look on youtube for "lithium battery fire" - there are some good examples and how they are dealt with - especially in difficult situations like laptop computer fires on aircraft.

[The Natural Philosopher]

Actually its LESS sophisticated, but radically different, usually.

Not in the batteries I use for models :-)

Actually they are not half as flammable as they used to be.

The simple crude way to charge lithium is to put a voltage limit of 4.2V per cell and a current limit of the capacity divided by one hour. So ou charge a one ampere hour cell at one amp max, and limit the voltage to

4.2v. That is crude and works.

The smarts happen when you want to reduce charging time to less than an hour.

Some packs have clamp circuitry so the series charging of several cells wont overcharge one cell. That helps if the packs are made from a bunch of assorted crap of variable quality.

Consumer packs will also cut the pack voltage if it drops below a minimum.

There is some tendency also to put charge circuitry in the pack itself.

Overcharging and overdischarging are the two killers of cells.

we used to charge in firebricks or garden posts. The burn out quickly.

All the cells WILL go up. Anyway. Its no big deal. You dont get trade in on a burned pack.

The later cells - lithium iron cobalt I think, are far far more tolerant of abuse. A123 cells - those have 3.7v terminal charge IIRC, dont explode and burn and can be somewhat over charged and discharged. For power tools the better choice really.

[The Medway Handyman]

Ah. The charger is 500m/a IIRC. The battery is 1.3 a/hr.

I take it I can 'opportunity charge' without problems?

They reckon 3 - 5 hours to charge fully. As long as the tool works Ok I'll buy another battery.

The tool has an LED worklight which flashes when the battery is low, and a cut out which stops the tool completely, so it looks like its covered by that on the over discharge side.

[The Natural Philosopher]

yes. ideal is half charged for storage.

Well that means they have something utterly crude like a stabilised voltage source and a resistor in series to limit the current...

that may or may not be in the battery pack. I'd say not. I can't remember what the 'dangerously low' voltage is on a cell - something like 3.3v IIRC.

When we fly these packs they are always in the plane or on the chargers..enough packs and chargers and you can fly continuosly - till the car battery goes flat anyway :-)

[Mark Evans]

Also the most common way to remove heat, water, is worst than useless when alkali metals are involved. About the only obvious method would be liquid nitrogen. Probably why such batteries are considered "hazmat" by the air fright industry.

[The Natural Philosopher]

there is no alkali metal in a LI battery.

There is a stable lithium salt in an organic electrolyte tho.

[John Rumm]

Don't forget that the posher laptops use magnesium cases rather than plastic.

[The Natural Philosopher]

well that's an aluminum magnesium alloy...

[Steve Firth]

Mark Evans wrote: [snip]

The main reason that the airlines don't like batteries is that they are either extremely alkaline (Lithium Ion) or extremely acid (lead acid). Aircraft are made from aluminium.

[Grimly Curmudgeon]

LiMnxx are v.tolerant of some abuse, it has been found. Google 'Konion' cells.