Question on safe min. LiFeP04 voltage & Bamboo Pics

[EZgo]

View attachment 5I have 5 fully charged 12V 10ah LiFeP04 SLA Bamboo Replacement Batteries from Clean Republic. Each one puts out 13.7 volts according to my Fluke meter & between 13.76 & 13.79 with my Watts-Up meter. Since These do not have a BMS I use a Watts-Meter to monitor battery health.

I charge these bamboo batteries using a 58.4V LiFeP04 Smart Charger from battery space & 14.5VLiFeP04 Smart Charger from Clean Republic. When my bike is fully charged & I turn it on my meter always reads 68.88 volts. (later I will start charging with SLA chargers to determine the differance, if any)

My question is: If I decide that the minimum voltage for these batteries is say 55 volts. Is that the resting volts or the minimum voltage under load? (the sag) If it's the resting voltage should there be a sag voltage threshold? I'm also not 100% sure why I always get an identical 68.88 volts. In theory I should get 73.3. When I check the 4 batteries charged with the 58 volt charger they measure 58.6 volts & the 1 battery charged with the 14.5 volt measures 14.7. when I hook them together & turn it on, the Watts-Up Meter reads 68.8. (The + wire is hooked to the on/off switch) I'll have to do some further testing on that little discrepancy. For now I just need to know how far can I run these things down.

Previously I had a question using SLA chargers for LiFeP04 battery packs. See Using SLA chargers for LiFeP04 batteries in this same section. I got a lot of good feed back & thank you for that. I also had a comment from Bob that said in part:

by dumbass » Fri Jul 19, 2013 6:58 pm "I would love to know the dementions of the cells without the bambo box around it. And what type of cells are actually in the box. Maybe without the bambo boxes there might be room in the stock Currie battery box to also fit a small BMS. "

So here is my take on these bamboo batteries along with some pictures of what they look like inside.

Months ago when I bought my 1st bamboo battery it was to test it & then take it apart. Long story short over a 2 month period I bought about 18 more of them. I did a lot of testing & built 3 36 volt bikes & 2 48 volt bikes. 1 48 volt is sold with a 48 volt sla charger. Another 48 volt is in my shop along with 2 36 volt bikes. I'm currently testing the 48 volt bike & charging it with a 58.4 volt LiFeP04 smart charger from battery space.

OK then,... this is what a 12 volt 10 amp LiFeP04 SLA replacement battery by Clean Republic looks like on the inside. I was hoping someone else would have done this by now. For now it is neatly cut open & I can put it back together & continue using it. I'm sure someone out there can identify these cellls with out me tearing the whole thing apart. Here is the nitty gritty.

Inside dimension of the box is 2 5/16" W x 5 1/2" L x 3 7/8" H. There is a 1/4" space between the end of the battery & the case at 1 end.

Each cell measures 1 1/8" x 2 1/2" L. . Unless there is an empty spot inside, there is room for exactly 12 of these cells. The voltage is 14.27 & the total weight of the battery is 2lb 9 oz.

My 48 volt bike at the moment is running 5 of these. Hot of the charger the Watts up meter reads 68.88 volts. 30 minuets of normal running brings them down to 64.35 volts. In that condition if I open it up from a standstill on an uphill grade (no pedaling) it will just hit 22 amps & dip to 58.82 volts by the time it hits 22 mph uphill it goes to 20 amps & 61.44 volts. When I hit the leval I'm doing 25 at 7 amps & back to 64. volts. To charge my 5 battery bike I use the 58.4 volt LiFeP04 smart charger from battery space & a 14.8 volt LiFeP04 charge from C.R. (the one that comes with the battery)

Keep in mind that C.R. is selling these as a SLA replacement battery so it's quite possible they may last a very long time in that type of application.

The only comparison testing I've done has been a seat-of-the-pants test using the above bike with one battery removed & an identical 48 v E-BikeKit using a 48 v 9 amp SLA battery pack.

The results?.... Their is HUGE difference in the first 60 seconds & it gets progressively worse pretty quick.


I have pictures of the bike on my blog at: http://ezgo-now.com/local-sales/night-rider-the-ultimate-e-bike-for-work-or-play. I'll try to update this as I learn more about these batteries.

 

[arkmundi]

I have 5 fully charged 12V 10ah LiFeP04 SLA Bamboo Replacement Batteries from Clean Republic. Each one puts out 13.7 volts according to my Fluke meter & between 13.76 & 13.79 with my Watts-Up meter.... My question is: If I decide that the minimum voltage for these batteries is say 55 volts. Is that the resting volts or the minimum voltage under load? (the sag) If it's the resting voltage should there be a sag voltage threshold?

Every battery cell has a minimum discharge voltage, a fully-charged state voltage (nominal), and a maximum charge voltage. The rule is don't ride past minimum and don't overcharge past maximum. The voltage on the Watt's Up or other meter will fluctuate, but will mostly be around nominal. LiFePO4 cells have a nominal ~3.3V nominal voltage. Safe maximum is 3.6V and safe minimum around 2.4V. Note that I specified everything per cell, because that's what you should be paying attention to. Overall pack's can show you within range, but a cell or two may be wacked out low or high. You may want to investigate a balance harness (leads to each individual cell) and Celllogs to do that. You have 5 packs of 4 cells each at a minimum 2.4V per or ~48V - 55 volts is hence within a safe range as a pack. Your real worry is a wacked cell that keeps charging high and you'll never know until its dead.

 

[dogman dan]

Minimum is resting voltage. So figure out what your normal sag under load is, near the end of the discharge when it gets a bit bigger, and add that 2v or whatever of sag to your minimum you look for as a stopping point.

In case that wasn't clear, say you want to stop at 55, and you know you have 2v of sag when cruising 20 mph. Then you need to stop when you see 53v while cruising at 20 mph. Once you stop, you will still have 55v.

Nothing wrong with stopping sooner of course. As you near the very very end, you might want to slow way down to a point where you can ignore sag, and just read the voltmeter with no corrections.

As for the discrepancy, my extra cheap watts up knock off had to be adjusted. It was not that well calibrated. Maybe yours is just off a few volts too.