I want to buy a cordless drill

[usenet]

I've just done exactly that with my 18v NiCd battery and charger from B&Q. It's one of their Performance Power range and is common to a whole lot of their cordless garden tools (I have the mini chainsaw lopper).

It turns out that, to my mind at least, they've done it the most expensive way possible, so much for shaving off the last few cents.

It has a fairly solid looking transformer rectifier power supply, full wave rectification by the way, no corner cutting there. There are then various indicator LEDs, a microswitch (with an external button to press it) and a latching relay. There are *three* connections to the battery, one of which is a temperature sensing one, when the temperature rise indicating full charge is detected the relay is latched off.

As I said, this surprised me, because it makes the charger relatively complex. A crude rectifier and series resistor would be cheaper and so would a delta/V detecting IC. As it is they have to have a latching relay in the charger, three connections to the battery and a temperature sensor in every battery. Certainly not corner cutting to my mind.

[Pete C]

Yes, you want the highest possible battery voltage and biggest possible cells. It doesn't matter that they have the same torque and the Ryobi is 50% heavier...

cheers, Pete.

[Pete C]

Hi,

If there are two or more battery packs, they can be used in rotation. cheers, Pete.

[Andy Hall]

This would all be a point if you were considering western component costs and labour rates. The electromechanical components are very cheap indeed and the labour rates to assemble them a tiny fraction of western levels.

The charger you describe could be put together by virtually unskilled labour whereas as soon as ICs and PCBs are used, the game changes.

.andy

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[Andy Hall]

Of course they would, but the other factor is the skill level in assembly.

They would be if you ignore the skill and labour factors.

.andy

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[Dave Plowman (News)]

Care to clarify? As far as I'm aware, all standard car batteries can be charged at the same rate pro rata with size. You have to take more care with similar size SLA batteries and they're more expensive, but that's probably just economies of scale.

[Dave Plowman (News)]

Still not a brilliant way of doing it, though, as it's unlikely all cells heat at the same pace, and the sensor will only be on one.

[Dave Plowman (News)]

Perhaps you'd then give us the benefit of your personal experience charging good quality batteries?

Oh - I forgot. You only buy s**te tools. Except for the hacksaw you use for most things...

[Andy Hall]

I guess that there's a difference between buying and being.....

.andy

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[IMM]

..yes "being" a lot better off in the pocket.

[Ed Sirett]

Well you could do much worse than the £75 DeWalt from Screwfix. I have one it works well. It is not the same as the £200+ Makita or DeWalt units. But it is well made comes with a 1 hour chargers, 2 batts and some bits. The torque control is quite stiff but I expect it to loosen up over a few years hard use, if it is not stolen prior.

You'll likely be about to drill masonry with _sharp_ masonry bits and firm pressure. The higher torque settings are quite capable of snapping the head of a 4mm screw.

[John Rumm]

Ironically its a technique that would work better on a more expensive battery pack where someone has taken the time to more closely match the cells.

[Capitol]

How would you match the cells? Just intrigued. Economic?

IME, cell life is a pot luck exercise. I find that batch A last x years and batch B from the same manufacturer don't, in the same application and charged in the same way. It does seem to depend on the manufacturer to some extent, but nor reliably IME.

Regards Capitol

[John Rumm]

The way it is often done is with a A to D converter on a computer and a resistor bank for a load. You charge up each cell until "full" and then connect up to your discharge rig. This then records the discharge over time, and allows you to plot a discharge graph. Then having done it with a bunch of cells you can cherry pick ones with closely matching curves for making into a battery pack.

You can buy cells that are already matched (at a price premium), or you can match them yourself. The "fast electric" RC model guys who are serious will typically do the matching themselves.

(I met a truly fanatical fast electric boat anorak once, who delighted in talking me through the details of his particular boat - kevlar / carbon fibre hull, 12 pole motor, 36 computer matched sub C cells - a couple of grands worth all in. This boat was designed to race for 500m round a triangular circuit - apparently it is a layout that is typically used for record attempts. To be considered "good" you should be able to do the three sides, a 180 turn at the end of the last, and then another

2 sides to the finish in under 20 seconds (at the time the record was something like 14). The battery pack would typically be expected to dump most of it charge in that time - developing a power output over 2kW!. After each run he would then hook the whole pack up to a discharger for a little bit before using a shunt with an a old galvo wired up to individually discharge each cell to 1V before he would fast charge the whole pack again.)

Hence the need for matching. Some brands do seem consistently better than others (e.g. sanyo, panasonic) - but as you say there can be quite dramatic differences between apparently similar cells.

[Andy Hall]

Because of the "he-man" handle?

.andy

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[MJ]

This sounded like the one I got there for £50 at the same time but it turns out mine is a PBX model. 2 yr warranty. Just like the last cordless drill I bought, I'm expecting the drill to outlast the batteries.

The earlier comments requesting proof that fast charging shortens the life of nicads - this is common knowledge in the modelling world (cars, planes etc) and has been for years. Likewise prolonged storage without use leavng the battery to self-discharge below its minimum level (1.1v per cell IIRC).

MJ

[usenet]

What I meant was that car batteries are *much* cheaper than the equivalent capacity lead acid batteries designed for long term trickle charge and deep discharge applications (i.e. traction batteries and alarm backup batteries). A car battery is designed to cope with high discharge rates (starting) and high charge rates (the alternator will pump in tens of amps at times). A traction battery of similar capacity won't cope with use in a car at all well, but on the other hand will cope with repeated deep discharges OK. Since car batteries are produced in much larger quantities they tend to be a lot cheaper, I think that's probaly the only reason, I don't think there's an inherent technical reason for the difference in price.

[usenet]

It *is* on a PCB, the latching relay is of the 'looks like an IC' variety. The assembly costs of a charger with a delta/V chip instead would be near enough identical, if not a little cheaper because there wouldn't be the additional complication of the temperature sensor in the batery.

You're not seriously trying to persuade me that the PCBs, chips, etc. used in 'expensive' tools aren't assembled in the Far East are you?

[usenet]

Yes, delta/V would be better and, probably cheaper.

I was just trying to show that a 'cheap' tool doesn't necessarily have corners cut in the electronics.

[usenet]

One of the major advantages of an IC base solution is that very little skill is required to assemble and test. Stick the components on a PCB, slap it all together and it just works, no set up or anything is required.