I replaced my lawn mower's Pb batteries with LiFePO4 today

[philaphonic]

Today I replaced my Black & Decker CMM1200's pair of Lead Acid batteries with a pair of LiFePO4 batteries from manufacturer GBS (bought them here: http://www.electricmotorsport.com/store/ems_ev_parts_batteries_lpf_gbs_20ah.php). Note that with shipping, insurance, and credit card surcharge, these weren't exactly cheap at about $350 for a pair with cell balancers. I didn't do this for economic reasons, but if they last 3 times as long as the last set of Leads I guess I'll break even. I am expecting the benefit of more stamina and lighter weight.

I photo-documented the surgery here, if anyone's interested: http://s106.photobucket.com/albums/m276/floating_ground/Black_n_Decker_CMM1200_gets_Li_batteries/

 

[adric22]

I have the same mower. Been using it for 10 years now. I've replaced the batteries 4 times. They typically don't last more than 2 or 3 years. The original Panasonic batteries lasted 4 years, but I'm always cheap and use no-name brand batteries when I replace them. I've thought about replacing with Lithium or NiMh, but I knew it would also require replacing the charger and probably need to add a BMS of some kind.

 

[GaslessInSeattle]

let us know how you like the performance.

a little off topic, I ordered Li-ions for our roomba a few months back, not noticing they were for a different model (web side was pretty bad)... they ended up getting sent back. If anyone knows of a good site for roomba li-ions for the 500 series roomba, plase let me know, our original battery is on it's last legs after 2.5 years and several resets and I would love to stop supporting NMH production.

 

[philaphonic]

I have the same mower. Been using it for 10 years now. I've replaced the batteries 4 times. They typically don't last more than 2 or 3 years. The original Panasonic batteries lasted 4 years, but I'm always cheap and use no-name brand batteries when I replace them. I've thought about replacing with Lithium or NiMh, but I knew it would also require replacing the charger and probably need to add a BMS of some kind.

I'm betting that the mower's built-in charger will do the trick along with the cell balancers. If not, I'm out some bucks for sure.

 

[philaphonic]

let us know how you like the performance.
((snip))

Tonight I dine, tomorrow I mow!

 

[GaslessInSeattle]

Nice!

My guess is that, like the leaf, not leaving it at a high SOC for prolonged periods, figuring out the time it takes to charge to "roughly 80%" and using a timer to shut off, not overworking the battery to the point where it gets hot and not recharging the battery till it's cool could make a big difference in long term performance. before I knew what I was doing I toasted an expensive Li-ion drill battery by working it too hard and charging it too hot.

Now I charge my drill/power tool batteries to approximately 50% and top them off relatively close to when I use them.

let us know how you like the performance.
((snip))

Tonight I dine, tomorrow I mow!

 

[DaveEV]

Today I replaced my Black & Decker CMM1200's pair of Lead Acid batteries with a pair of LiFePO4 batteries from manufacturer GBS (bought them here: http://www.electricmotorsport.com/store/ems_ev_parts_batteries_lpf_gbs_20ah.php).

I want one of those batteries with the appropriate BMS integrated so it will work as a drop-in replacement for your typical 12V lead-acid battery for cars - like the one under the hood of the LEAF, for example.

 

[garygid]

CAUTION:
A Pb charger typically/sometimes keeps (trickle) charging
a "full" battery, even after reaching about 14 volts.

Usually, that would "kill" a 3-cell Li battery by overcharging it.

Edit: Closer look, I see you have 4 Li cells.
At 3.7v x 4 (and balanced!) they might take 14.8 volts,
but overcharging (and over-discharging) is still a possibility.

Any more details on your charger and/or the BMS?

Does the BMS protect all 8 cells, individually (needs a wire to each cell)?

What keeps the battery from over-discharging?

 

[stanley]

I need to buy a new mower to cut about 1/3 of an acre. Would a battery driven mower work and if so which one would you recommend?

 

[DaveinOlyWA]

battery mower has GOT to be more convenient than mine with its 100 ft extension cord. my yard is small enough that i only have to use 3 different plugs (2 for front, one for the back) but still a hassle to mow since pattern cut is somewhat limited to prevent me from running over the cord.

but i will run this one until it dies which maybe quite a while. the blade should be sharpened so will probably get that done before mowing season starts in about a month or so.

 

[Herm]

4 cells LiFePO4 (assuming they are balanced) can be kept floating at 14.4V indefinitely, 100% charge.. it wont hurt the battery unlike other chemistries of lithium-ion

 

[garygid]

If the cells are balanced, AND the charger STOPS charging at some voltage (under about 15 volts), the cells will generally be OK.

However, a "Floating" charge usually means "continuing-to-charge" (at a low current), forever.

Unless the BMS can bypass this "trickle", the 4 cells can continue to charge up to over 16.4 volts, into "unhealthy land".

I have 21 similar (not the exact same) Lithium Iron Phosphate battery cells in my Motorcycle, and going over 4.1 volts per cell is NOT the best (or even a good) idea, in my opinion.

 

[DarkStar]

Here's a link to the info on those balancers with the 20 Ah battery: http://elitepowersolutions.com/products/product_info.php?cPath=25&products_id=146" onclick="window.open(this.href);return false;

It looks like they can bypass 0.5 amps each (at 3.55 volts), for a total of 2 amps for the 4 cells. If your charge rate is kept below that rate and 14.2 volts you should be golden!

 

[philaphonic]

Here's a link to the info on those balancers with the 20 Ah battery: http://elitepowersolutions.com/products/product_info.php?cPath=25&products_id=146" onclick="window.open(this.href);return false;

It looks like they can bypass 0.5 amps each (at 3.55 volts), for a total of 2 amps for the 4 cells. If your charge rate is kept below that rate and 14.2 volts you should be golden!

The lawnmower's charging circuit appears to be all up in the handle and at this point in time I'm not interested in taking it apart to examine things. I haven't be successful in finding a circuit diagram or specs on it, either. There is a separate brick power supply, with 3 wires, listed as 26 VDC at 1.5 A. I measured an open circuit voltage of 27.65 VDC between center and one side, and zero volts between center and other side. (Remember, there are two batteries in series, for a "24-volt" mower.) The 3rd wire might be for signalling the brick, since the brick has a red/green LED that indicates charging status.

For what its worth, I emailed the seller before purchasing the batteries, asking specifically about the charging issue, and while they may not be unbiased, they believed it would work okay.

 

[gbarry42]

It looks like they can bypass 0.5 amps each (at 3.55 volts), for a total of 2 amps for the 4 cells.

4 x 0.5 amps is still 0.5 amps, if they are charged in series.

 

[DaveEV]

The lawnmower's charging circuit appears to be all up in the handle and at this point in time I'm not interested in taking it apart to examine things. I haven't be successful in finding a circuit diagram or specs on it, either. There is a separate brick power supply, with 3 wires, listed as 26 VDC at 1.5 A. I measured an open circuit voltage of 27.65 VDC between center and one side, and zero volts between center and other side.

WIth a 27.65 open circuit voltage you shouldn't have anything to worry about. Did you get the balances with your batteries? Seems like a good idea to protect your investment...

 

[TLeaf]

I need to buy a new mower to cut about 1/3 of an acre. Would a battery driven mower work and if so which one would you recommend?

We've had our Black & Decker electric mower now for 11 years and are still working on only our second set of batteries. Of course, it helps that we have only a 50'x40' lawn that we're mowing, but I would think a 1/3 acre MIGHT be possible. Important tips would be: 1) mow frequently so the grass never gets too high, 2) don't drain the battery dry then immediately plug it in (you'd risk overheating), 3) perhaps mow half of the lawn at a time, 4) go with the higher cost Panasonic batteries (as original).

 

[stanley]

TLeaf, Thank You !!

 

[TurboFroggy]

I have done this conversion already with my CMM1000 Black and Decker Mower. I got a 20AH 24 Volt LiFEPO4 battery pack from Ebay. My mower is just pushing 10 years old and had already gone though sevral recall/redo's from B&D, so it had the latest handle, charger etc with it. The pack that I bought had a built in BMS in it and came with it's own charger. I re-wired the connector for the charger that came with the pack to the connector that went to the handle so it can just plug into the same location on the mower. There is a diode inline in the handle that must be bypassed otherwise the charger won't work right.

I was able to turn the styrofoam that held the lead batteries sideways and press-fit the new pack into the same spot and using the same strap. The BMS did not allow for a high enough inrush current so had to put a switch on it to temporarally bypass the BMS while starting up the mower. It is at least 20 lbs lighter than before and the battery does not slow down clear until the BMS cuts it off. Charging it fully automatic with the built in BMS and takes around 4 hours (5 amp charger).

I also put a battery guage with a push button check so I can easily tell the battery level. After three seasons it is still working fantastic.

https://skydrive.live.com/redir.aspx?cid=fba3b570731942ad&resid=FBA3B570731942AD!9700&parid=root

 

[philaphonic]

The lawnmower's charging circuit appears to be all up in the handle and at this point in time I'm not interested in taking it apart to examine things. I haven't be successful in finding a circuit diagram or specs on it, either. There is a separate brick power supply, with 3 wires, listed as 26 VDC at 1.5 A. I measured an open circuit voltage of 27.65 VDC between center and one side, and zero volts between center and other side.

WIth a 27.65 open circuit voltage you shouldn't have anything to worry about. Did you get the balances with your batteries? Seems like a good idea to protect your investment...

Yup, got the balancers.