Tuesday, 11 November 2014

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

Old cordless drill with a bew batterty pack
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.  :-)

LiPo vs NiMh
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. 


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  5. This is really good!! My father found a old hitachi drill with its battery power and it doesn't go coz it's been up on the house roof for years