Li-ion external drill battery advice

[underground]

Please can any of our electronics/digging experts help me on this?
I'm informed that it is now possible to build such a pack (pelicase packed cells attached to a drill body by fly lead) using cheaper li-ion cells from the likes of deal extreme?

I'd appreciate any help and advice, from a shopping list of components, to how to go about building the thing. Also how to go about recharging and keep the cells in good condition...

Thanks 

 

[SamT]

Yep - I too am interested in this.  I've got one of Nick Williams' excellent Pelicase packs with 24v of F Cell NiCads, still going strong. 

I too was wondering if something slightly smaller/lighter/cheaper could be done with li-ion cells instead (lets not worry about the casing for now)

So - what's the craic with getting hold of some Li-ion Cells - I'm interested in both 36v and 24v - and an appropriate charger.

In the back of my mind, I've got it that its harder to charge Li-Ion's correctly, and all sorts of electronic jiggery-pokery may be required.

 

[underground]

Having looked at DX just now there are loads of 'lithium' batteries available. I'd also be interested in seeing some basic maths, ie how to spec the correct size/capacity etc

 

[Benfool]

Be careful of lithium 18650s off DX, a lot of them are pretty crappy and the capacities are well below what they claim to be. Better off getting properly branded 18650s from Japan, sanyo and panasonic seem to be good and is what is used in both the Rude Nora and Scurion.

Any idea what sort of current your drills pull at peak? Might start doing a little bit of research into this as there seems to be a fair amount of interest.

 

[kdxn]

Could also consider LiFePo (Lithium Iron Phosphate) technology.

Ready made large capacity battery packs and chargers for eBikes with and without case.
eg.
http://wooshbikes.co.uk/?batteries

Large capacity Lipo packs here:
http://www.jozztek.com/shop/6-batteries
and they do a charger here:
http://www.jozztek.com/shop/9-battery-chargers
They can do you a custom pack.

Lots of other options out there but would echo the earlier post that it is better to pay a bit extra for good quality cells.

 

[jarvist]

If you're running at 24/36V have a look at pre-maid 24/36V LiFePO4 packs (search eBay) - they're sold mass market (in 10-30Ah packs, with chargers) for powering electric bicycles, and the larger ones should be sufficiently spec'd to run at the current of a drill. I think this would be perfect if you want a mother-load battery to run a digging drill for a long session.

For bolting on expo Imperial has gone with lightweight NiMh Sub-C packs (for our Bosch Uneo and Makita - both run at 14.4V). These were cheaper per Ah than equivalent lithium when I looked, and could sustain a higher current in these small packs. Building a big Lithium battery out of 18650 cells is a real headache due to having to wire up the batteries in parallel (individually they only have a 2Ah capacity or so - just the same as a NiMh AA battery, but at higher voltage) & balance them when charging (so you need lots of little leads from the individual cells going to a wiring loom to a complicated charger).

 

[underground]

In my case I've been given a 24V Dewalt, without batteries, obviously an ideal digging drill candidate - highly unlikely to be used on a pitch, but now - if I can get it powered up - highly likely to be transported to a dig and used for digging applications.
TBH I don't mind on the chemistry, but a weight reduction would be an obvious bonus wherever possible - that said, there's a balance point somewhere where cost and complexity of charging etc. is likely to dissuade me.

 

[Nigel]

About 18 months ago I bought a 24v Erbauer sds drill from Screwfix. This comes with two Ni-Cd batteries which on first use did about 2.5 holes (12mm X 150mm) to be fair with use this did improve to about 4 per battery. I decided to try building a li-ion replacement and found I could fit 7 pairs of cells in the original case (sourced from replacement laptop batteries) giving 25.9v on load for most of their charge. Not only was this pack lighter but instantly gave 12 holes per battery. Now to charging, the criteria is to limit the initial charge current until voltage rises to 4.2 then clamp voltage at that level until the charge current drops to about 3% of capacity then switch off. This is fairly easy to achieve so I rebuilt the charger to suit. The problem with this simplistic approach is that the cells soon start to drift out of sync meaning that some get over charged when recharging and the others get over discharged in use(laptop batteries use clever electronics to monitor each cell and equalize the charge each time, this was beyond my abilities). My solution to this has been to open up the battery pack and manually monitor the battery voltage and then top up low cells with a bench top power supply about once a month or every 4 charges.
Cost about ?30 (2 X laptop batteries and parts for charger).
Life span 12 months with weekly use before performance dropped noticeably.
Of course it is then just a case of identifying the faulty cells and replacing them. I realise this is not going to suit everyone but may help. Has anyone got a better way of doing this as lithium ion is definitely worth the effort?

 

[underground]

That's encouraging, thanks Nigel! Are the laptop packs you used to repack the battery a specific type?
I have to admit I don't know where to begin with modifying a charger, but I'm willing to learn. Is it a hard job?

 

[Nigel]

Re Laptop batteries I just bought 8 cell replacement packs from eBay. These contain cells already welded in pairs so two packs give you 7 pairs for the drill and one spare. I suppose modify the charger might have been a bit misleading as I think I only kept the transformer and rectifier but I will post a circuit diagram for if you are interested.

 

[underground]

Yes please Nigel. Worth a try for the money for sure

 

[Nigel]

Will do but it may take a couple of days to find it.