Ryobi battery Build - Am i ready to test?(update: success)

jssneptune - You might be right about paralleling 3 packs and using the original charging circuit forming a 18v 12AH pack. Some guy made this on youtube:
supersize_ryobi.jpg

I was also wondering the exact chemistry of the samsung 18650 20Q, if it is similair to Dr. Bass's Konion self balancing type. I've been searching and reading posts as far back as 2009.
I'm hoping some other ES user's could chime in with recommendations for my second Ryobi build:

9 x Ryobi 18v P108 4AH
1 x stock charger P118 ( faster charger )

convert into 3 x Ryobi 18v 12AH, then connect into series to form a 54V 12AH with the ability to separately charge using the stock charger. So yea, exactly what jssneptune was mentioning.
The 2 concerns I have are balancing cells & whether or not the stock charger can safely charge a 12AH battery in 3hrs ( quick charge ). My preliminary research tells me ' sure no problem, piece of cake ', but I can't learn if I already know.
I'm also interested in using the built-in fuel gauge, but does it just measure voltage or count coulombs? I thought I knew what I was doing, but the more I read these forums, the less I am certain.
 
After re-reading some old threads about ryobi p108's, I realize they are capable of 7.5c which allows 30A. My pack is 54V 8Ah, so it's capable of 60A. The fuse is 40A and I think this leaves a pretty good margin of safety. The range may not be great, but I'm not using this to do a daily commute ( yet ). Here's some pics that i hope encourage other to mess around with ryobi p108's.

1st pic is the finished battery, I can share the pdf(to scale) and wire diagram if you pm me. If there is a way to share it publicly, let me know.
2nd pic is mounting options and I haven't figured out yet. I've been riding with it mounted on rear. If I ever get stopped by NYPD, I can easily explain what the packs are originally for.
3rd pic, I like voiding warranties and wanted to show the cool battery meter on the fancy bms. If anyone know's exactly how these work, I would really appreciate it.

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Love this idea and your implementation. I was looking for a way to get a pretty light low ah 36volt battery, something like 3 - 4 ah.

I've got a couple of the Ryobi batteries already and will give this a try and post my pics.
 
I love the 2x4 implementation! This is a pretty cool way of doing the modular battery idea. I've been toying with trying to figure out ways of making this work for ebikes in general. Want ppl to be able to build their own packs, build a simple case for them, and then insert them into a space on the bike (much like a tool pack) and go. Eliminating the plug-in lead has so many advantages!
 
mclark999 - I think it should work fine since the pack can do 7.5C which allows 30A. If you can monitor your amps, you should be ok. I had one of the packs lose a connection, which essentially made my pack 54V 4Ah. It got warm and drained pretty quick. Looking forward to your build.

dequinox - Using power tool batteries as a modular pack for ebikes is an idea that has been tossed around on endless-sphere for a while. The new tech in power tools is brushless motors and the battery tech has improved incrementally. BTW, I've read your posts on recycling laptop batteries. I'm really impressed by your dedication and I hope it works out for you. It's great to see members on this site, document & try out their ideas.

Thanks for the compliments! I've been testing for reliability to improve the design.
 
brooklynboy said:
mclark999 - I think it should work fine since the pack can do 7.5C which allows 30A. If you can monitor your amps, you should be ok. I had one of the packs lose a connection, which essentially made my pack 54V 4Ah. It got warm and drained pretty quick. Looking forward to your build.
Click to expand...

If I used 2 of the 4Ah batteries with a controller that has a LVC, I'm thinking it would just shut off if one of the batteries disconnected. Wouldn't make my wife happy, but would save the battery. :D

I also found a Bosch tool battery that is 36V in a single battery, but its $200 and I'd have to buy a charger.

Hoping I can find a great deal on the batteries. Currently I can get a 2 pack from HD for $100 which is pretty reasonable.
 
There is a site called slickdeals dot net. You can sign up for alerts to ryobi batteries, specifically p122's. I think sometimes with coupons you can get them for 85 to 95$. If you wait, they may go on clearance down to $75, $50, or even $25. There was a ryobi promotion recently at Home Depot for father's day, so some stores may have overstock that may go on clearance at a later date.

Also note worthy is the P125 dropped in price to $60, but it only charges 1 at a time ( roughly 2hrs/battery).
p125.jpg
 
Y'know it's not the absolute cheapest option possible -not like a 2x4 hogged out with a rasp cheap- but that multi charger is the skin, bones and meat of a six-way toolpack onboard factory engineered rack sitting there -and for about sixty dollars- nearly completely built.

Go inside and add an appropriate switch, plus wiring and connectors, etc. to isolate the charger hardware, output the toolpack terminals as 3S2P (or what have you) to a standard controller connector and wah-lah!

A weight weenie could excise the charger hardware, but I myself would carry it around as an always available way to snag a charge from any handy housepower outlet. Even at home or work.
 
There is a youtube video of the P125 being disassembled. The spring contacts are directly soldered onto the main board. Which means I would need to scrape away traces and solder switch(s) to isolate the charger hardware. It sounds simple to cut 12 traces, but it depends on the layout of the board. It's great suggestion and I would love to someone do it.

The second thing I worry about is how it will hold up bouncing around on the road. It's mounting holes were made for hanging on the wall. The most practical way would be flat on the rear. My 2x3 has some dents and chips from riding around at 25mph.

I have to admit it would be a decent option to do this for a 36v 12ah. Ebay has a few broken p125's that I have been looking at for a few months. I doubt I'll attempt this mod any time soon. Thanks though.
 
Awesome setup! Have you confirmed that both parallel banks are drawing down equally? A problem I ran into with P108's was that when they are paralleled, one would be shut down by the bms. (When sitting idle, the main terminals do not output 18v on these batteries.) I ended up using the "guages" as connectors in order to keep both batteries active.
 
Hey fellow ryoberry user! The 2 banks drawdown equally to within .01 volts of each other. There was one occasion where 1 single 18v self discharged, but I could not pinpoint the problem. I simply mounted the springs more solidly to provide better contact. The batteries didn't need to be activated or kept active. It might be due to the higher voltage in a single bank 18v X 3 = 54V 4AH and then parallel. I also can press the built in battery gauge on each of them to check capacity while they are still wired up. The built in gauges did not blow ( I think they are isolated from main terminals and connected to bms ) . After a ride, I press 6 buttons and I roughly know what capacity I have.
 
There's a new p135 ryobi charger that looks a little better built. It might be a good candidate for conversion depending on how it's wired. Hopefully they'll mark down the older model and I can try to mod it.
 
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