Rebuilding old Power pack, LiPo-edition (Hitachi B-2 for DRC-10K)

Drill with the first LiPo -pack I made some months ago.

Apparently my fathers venerable old Hitachi DRC-10K cordless drill fails to die, so once again there are need for battery refreshment build. Earlier days (see earlier post ) I did use NiMh cells, but the times have moved on.

When I checked the prices of those tabbed Sub-C cells from net, I noticed that can get a decent capacity LiPo power pack at the same price. So i decided to give these new packs a go, thus I did the first conversion some months ago.

Realistically it's only 1200 mAh if even that.

During this time I've been listening feedback from my father about this idea. And since he's happy with drill performance and lighter weight, I'm now making second LiPo battery pack, and finally taking couple pictures for this blog as well.  :-)

So much smaller and lighter.

One of the biggest advantage for using LiPo batteries in this kind of project is the wide availability of ready build packs. These packs are used on various radio controlled systems, like cars, planes and quad copters. On first version I  purchased brand battery and balancing charger from RC hobby shop.

For this second build, I decided to cut some corners (and cost). This LiPo battery shown on these pictures is a cheap Chinese knock-off, with obviously incorrect markings printed on. Also the size is somewhat smaller so I'd expect the real capacity being lower as well. Chinese sellers are well known on their inflated markings, but I'd expect this battery to serve well at this application.

Ready to close zip ties, balance port at left.

While comparing LiPo to NiMh, the size difference is quite noticeable.  One needs six NiMH's cells for 7.2 volts while there are only 2 cells at this LiPo pack I used as an replacement. And even thought those old cells had more power in them (over 2000mAh) while on optimal charge, the NiMh cells high self-discharging meant those batteries were rarely well charged the moment of need.

Charging with Turingy balancing charger.

In the end this conversion was not a big job. Electrically it's just desoldering and removing the old cells and connecting the new ones to existing battery pack contacts. The biggest part of work went onto B-2 -pack case modification. These rechargeable lithium batteries need to be balanced while charging, so there's need to have their balance port (white 3-pin connector shown) routed out of the pack.

At the time of this writing I have no idea how long these batteries will last, but I'd expect them to stay good at least few years. If the new charger behaves, there should be no problems for some time. 

Rebuilding old Power pack (Hitachi B-2 for DRC-10K)

Hitachi DRC-10K... Slightly used, like 30 years

My father has this three decades old Hitachi DRC-10K cordless drill and against all odds it has proven to be nearly indestructible. Unfortunately rechargeable NiCd batteries tend to wear out and thus need replacement sooner or later. Even thought 3rd party power packs are still available those tend to cost around 40 Euros (50USD) before delivery, taxes etc.. And quite frankly you can purchase all new cordless drill with price like that.

B-2 type power pack (once opened)

So.. Alternative is to replace the battery elements inside power pack. It's actually quite easy to do and saves easily over 30€ when compared of purchasing new pack. Of course it'll take some time and effort, but for someone willing to DIY and values recycling, it's the right way to go. 

Six new NiMh cells soldered together

First part of project is opening the battery pack and checking what type and size the batteries are. Opening the pack depends a lot of the pack itself. Hitachi's original B-2 battery is sealed with some kind of glue, so you'll need to use some real force and mechanical tools. I had opened this particular pack earlier (10+ years ago?) and by the looks of it, I must have used tools like hacksaw, sharp knife and screwdrivers. In the end the tools don't matter so much, as long as you don't break the cells inside pack or hurt yourself.

Heatshrink protecting joints

After opening the pack one has to check what size the rechargeable cells are. At B-2, there are six sub-C elements (size approx. 40*20mm). For this purpose it's convenient to use cells with metal tabs on them. Easiest way to get cheap replacement cells is to search net sellers from sites like Ebay. Unfortunately I can't really recommend any of those stores, since they tend sell whatever is available, thus there is no real guarantee of the quality or capacity of the cells.

After opening the power pack you'll need to unsolder the power wires from old batteries and start preparing the new ones.  First duplicate the layout of the batteries and solder metal tabs together. As these differ for each pack I can't give more explicit guide here. Just be sure to check polarities and cnnect the batteries just like old ones were and it will be ok.

Twist, test and solder power connector

With B-2 power pack it made sense to build two sets with 3 batteries each and bend them so that they fit into existing enclosure. I decided to use soldering which is ok, as long as on don't burn the batteries with overheat. I also decided to cover connections with heat shrink tube.

Next is soldering the power connector wires to batteries (remember polarity) and stuffing these renewed innards inside existing power pack enclosure. I decided to use some hot glue to keep power pack safely closed.

Rebuild powerpack alongside modified Hitachi charger

For testing I did charge the battery pack with modified hitachi charger. The original charger (30 years old) was designed for using with NiCD only. Since NiCD are harmful to environment I have lately been using NiMh batteries instead. With NiMh batteries there was need for new type smart charger (with Delta-V detection). As a bonus this new charger is also faster and can handle both types of batteries.

Old NiCd batteries I've used years ago

After a couple hour recharge, the power pack was inserted to drill and tested to be on working condition. I have not done any power tests so I have no idea how good these new batteries are, but I'll expect to hear comments as soon as my father needs the drill next time for some tinkering project he has.

And that leaves the last part, trash disposal. Making sure that those old used NiCd batteries I had used years ago at previous Rebuild will be properly handled and processed as an special garbage. I have no idea how harmful NiCd batteries really are, but at least in EU area those are under strict control, so one has to be careful how to dispose them.


Meta:

I know... I have not been making these updates as often I ought to, for keeping this blog interesting. So sorry, not having any good excuses either, no mystic NDA projects, no family issues etcetc..