12v Portable Power Pack from 56v cordless tool batteries

snowfiend

Active member
I have this build planned out but would appreciate a go/no go from others if this is a decent idea or not. I have a set of Echo cordless power tools which run "58v" 2ah or 4ah batteries. I have an extra charger and battery collecting dust, and would like to put it to use as a portable power pack similar to https://www.instructables.com/id/12v-Power-From-Ego-Power-56v-Battery/ while also retaining the battery charging capability. It charges the 2ah battery in ~30 min, an hour for the 4ah, so it opens up the possibility of topping off the battery if we go out exploring in the truck.

There is a pretty good teardown of these batteries HERE, they are 14s2p 18650 batteries (or 14s1p for the 2ah pack). If I use a 95% efficiency step down converter to 12v, that might give me a ~17ah battery [(56v/12)*4ah*95%=17.73AH]. The converters seem to have a draw even when not under load, so it would get a switch. 12v out would go to a couple USB ports, a cigarette style socket, binding posts, and maybe some sort of quick connector. I took the charger apart and there seems to be room for the converter in the base if I clean out a few plastic rib supports from the case. If I just use the binding posts and a small usb socket, I might be able to get it all in the OEM charger case. Otherwise I have a plastic ammo can that I can put everything in and would also offer some weatherproofing.

This would cost me ~$50 for the step-down converter, usb socket, switch, and binding posts compared to $325+ for a Powerwerks PWRbox + 20ah Bioenno battery + charger. Terrible idea, or go for it?
 

john61ct

Adventurer
Go for it, but I'd make it modular, to accept Ryobi One+ at 18V, Ridgid, Milwaukee etc.

If frequently cycled, such batts don't last long maybe a year or two.

LFP is the right chemistry if buying cells new.
 

john61ct

Adventurer
And don't trust ampacity rating of your buck converter, says 20A so maybe 10A continuous. Buy spares. eBay and AliExpress often much cheaper.

Old western telecom gear like Lucent, Emerson, even Lambda can sell NOS or second hand for 5% of the new price, **much** more robust and reliable.
 

snowfiend

Active member
I don't anticipate much load since it would be more for small electronics like phones, camera, radios, lights, etc. Not a fridge. Maybe one of those small diesel air heaters down the road, those draw ~9a at startup then only .5 or so once warm.
 

snowfiend

Active member
Converter, posts, and USB socket are on the way. If it doesn't work I'm out the converter (and hopefully not a battery!) but there are plenty of other uses for the socket and posts.
 

llamalander

Well-known member
I've been using 18v. Makita batteries to store excess power from my alternator/solar setup (I use them for work too).
A cheap buck-convertor lets me use them for 12v. devices and Makita makes a USB charger I can power devices with.
Here the USB charger has been adapted to run a pump in a freestanding sink unit that gets used in tents and cabins.
If you have spare batteries it's a fun project to make use of them.
Lithium is the best storage around, cordless tool batteries often have very robust management software which means you can use them with simple electronics and get good results.
It is worth checking if the Echo batteries have onboard BMS or if they rely on the chargers/tools to regulate the output & charging.
 

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snowfiend

Active member
Proof of concept, but I somehow misplaced my switches so I can't get it fully wired up in the case. Voltage dropped to 12.1 when I plugged in my phone to the USB-C port, but there is only a half charge on the testing battery.

Some light Dremel work and the converter fits snug in the empty base. There should be just enough room for the USB socket and the binding posts on the back panel (binding posts are going in the recessed handle).

Did some multimeter testing, with the charger plugged in to the wall no current flows to the battery holder until a battery is inserted and then it gets 54v at 5a. With battery in the holder but not plugged into the wall I get 56v on the charger back panel where I will solder on the converter (switch after the fuse on the wire to coverter). I will have to remember to turn the switch off when charging the battery, but worst case and I forget it will just activate the converter within it's parameters.
 

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snowfiend

Active member
Got a switch so I was able to solder on the converter. The USB socket is going to be tight and there is pretty much only one place to put it, so I'll see how it goes. Binding posts are getting moved too as they are longer than anticipated.

Wife is still confused about this project and why we need more battery power in the woods for electronics, not less. I told her "it's overlanding, don't worry about it" and she went back inside :p
 

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snowfiend

Active member
Attached is the wiring diagram, planning on sending the 12v to the binding posts then to the sockets. Should I fuse the + going from the post to the sockets? The USB socket says it has an internal non-replaceable 10A fuse, and the time and effort to wire in another 10A fuse might be more than buying a new socket.

The converter is rated at 20A, but I was thinking of putting a 15A fuse in the holder to offer some protection in the event it doesn't live up to it's rating.
 

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john61ct

Adventurer
Fusing is to protect the wiring against overheating.

It must be on the source side to do that.

Up to you if you think the risk is low, but consider the heat put out if the batt terminals get shorted.
 

snowfiend

Active member
Finally got around to a test run, it works well with the diesel air heater. I have 3 more batteries lying around, and got to thinking about paralleling them for more capacity (taking precautions to make sure the voltages are similar first). But could they also charge in parallel or do I have to remove each one and charge individually? Blue box is what I have now.

204 watt hours x 3 x.95 (buck converter efficiency)= 581 Watt Hours. 581wh / 12v = 48.45 AH battery pack.

Echo Power Pack.jpgIMG_20190205_210500.jpg
 
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