LiFePO4 replacement for lead acid battery

icepuck

With the recent and sudden price increase of gasoline( or petrol) and diesel fuel prices were I live has got me thinking of how I can revive one of my rechargeable push mowers. So far Pb batteries in my mowers last about two years. A set of new batteries is about 75% cost of a new mower.

When new, my 24 volt(2 20ah batteries) mower would mow my front yard on a single charge, last summer I could mow about 75% before needing a recharge.
For the 24 volt mower I've been looking at the following...

http://www.all-battery.com/Tenergy12.8V20AhLiFePO4RechargeableBattery-31943.aspx

Two of those would be $559.98 us.

And for my 48 volt(4 10ah batteries) mower I'd need four of the following...

http://www.all-battery.com/12.8V10AhLiFePO4-31383.aspx

For a total of $639.96 us.

I know that's a lot of money but once I've bought the batteries hopefully they will last longer than lead acid. At least I wont have to "buy it and burn it" like I do with gasoline and diesel fuel.

The reason why I'm considering this is I've yet to find a small diesel engine that would work for what I want, for mowing the small areas of my property.
-dan

Mike Green

I would do more research. These are LiFePO4 batteries and have fundamentally different chemistry than Lead-Acid batteries and very different charging / discharge needs. Presumably, these Lithium batteries have additional charging / discharge circuitry inside that makes them behave like Lead-Acid batteries since they're sold as drop-in replacements. Make sure these are designed to work properly in series (2 x 12V = 24V and 4 x 12V = 48V) for charging particularly. Lithium batteries have the unfortunate ability to explode and burn intensely when damaged, either mechanically or electrically although LiFePO4 batteries are better behaved than other Lithium batteries. Lead-Acid batteries do indeed last a few years at best under common conditions. They are normally recycled when replaced.

Humanoido

Battery operated vehicles are in a transition phase and will phase out most gasoline powered devices over time. Eventually fuel cells or an alternate energy source will be used. For now, Lithium batteries have fast replaced lead acid batteries. By comparison, they don't have the memory problems and can be deep cycled for longer operating times. They charge faster, charge a greater number of times, and have greater longevity. Their storage "no use" life is also longer and they weigh less.

A 36 volt front-drive VSC/PAP e-bike like this one can reach 40km with a lithium battery.
http://humanoidolabs.blogspot.com/2013/02/electric-bike.html

Franklin

Or you could try this...http://www.youtube.com/watch?v=_oEFwyoWKXo

NWCCTV

If you are mowing your lawn at this time of the year then you must have a lot of sun where you are. Why not go solar??? If that is not an option, I believe they still make the 110/220 V plug in mowers. Only downfall is running over and tangling up the extension cord. It would beat having to wait between charges and would take about as much energy as recharging the batteries.

Peter KG6LSE

Mike I have seen the 7 AH ones here at Frys the Only catch I have heard is discharge rate ........ Forget putting them in a UPS or a car Jump starter!

this is a Huge issue for a mower that may be drawing some serious juce ..

.5 HP is 1/2 X 746 watts = 373 watts and at 48 V is 7.7ish amps ..

Max. Discharge Current (Pulse) 70.0A
Discharge Method-Standard 3.8A
Max. Continuous Discharge 30.0A
the surge needed to get that blade movement could well excede 70 A for a few Seconds..... ( IMO a O-Scope and a DC shunt would tell ya a good " picture" of what the load is gonna look like and its curve)


perhaps a NiMH might be better .... and get a Nice charger too! I have personaly used and Abused the daylights outta the 10 AH ternergy D cells and have got my moneys worth outta them ..

LoopyByteloose

There might be some real advantages in LiFePO4 chemistry as the cells would take a charge faster than the Lead Acid. So there would 'in theory' be less down time.

But there are an awful lot of LiMnO battery packs sold by the Chinese with claims that they are LiFePO4 cells. Be wary if the math of the voltages is not right for the chemistry and the English is a very poor quality translation.

The bottom line is whether you are going to get more or less use out of the LiFePO4 for the $$$$ spent. In theory, you should as LiFePO4 are a Lithium ion chemistry that seems to make cells age graceful and last very long.

But the truth is that the wrong charger configuration can cause a premature end to any Lithium cell and lack of a proper low voltage cut off also does harm to the cells when in operation and away from the charger.

I just don't see how you can get all your ducks in a row to be sure the cells are the right chemistry, the charger is first rate, and the discharge protection is right. It seems we are in a period where there are an excess of large lithium cells available that are either other chemistry or less acceptable than the best technology. It is all buyer beware and DIY conversions are fraught with hazards. You would likely be looking at electric bicycle kits for your conversion choices and there is an awful lot of nonsense from these guys.

icepuck

NWCCTV wrote: »

If you are mowing your lawn at this time of the year then you must have a lot of sun where you are.

At the moment we are getting dumped on by anther snow storm.

NWCCTV wrote: »

Why not go solar???

I do have a small solar setup, 3 64 watt solar panels, xantrax charge controller and 600 watt sine wave inverter. For the past four years that's how I've been charging my mowers, 18 volt weed eater and anything else rechargeable.

I really like using solar because I don't have to burn any money(fuel) to cut the grass.
-dan

icepuck

Peter KG6LSE wrote: »

Max. Discharge Current (Pulse) 70.0A
Discharge Method-Standard 3.8A
Max. Continuous Discharge 30.0A

The 48 volt mower has a 30 amp fuse and I've never had to replace it.

Peter KG6LSE wrote: »

perhaps a NiMH might be better ....

I did find a 48 volt NiMH pack and charger but it was even more money than the LiFePO4s I've found so far.

I've also noticed that some LiFePO4's list an internal BCM(battery control module) and some don't. I wonder If that gives a clue as to the type of Li chemistry being used.

I've been trolling other forums that have anything do with Li batteries and some people claim that LiFePO4's don't need a BCM, is that possible? I would think for the type load I would be running that a BCM would be needed to protect from over discharge.
-dan

Peter KG6LSE

Ice . the fuse is a good Sign ! ..... then it really may work !

and those Drop in Li Lead batts are Really quite carefree for what they are .....

I've been trolling other forums that have anything do with Li batteries and some people claim that LiFePO4's don't need a BCM, is that possible? I would think for the type load I would be running that a BCM would be needed to protect from over discharge.

Oh NOOOOOO I would never use a Li based batt with out a fancy BCM...... Esp wiith series strings .......

LoopyByteloose

A lot of electric scooter and electric bicycles have an internal BCM (battery control module). Ideally, these make the charger much simpler and provide both charge and discharge protection to the series of cells.

But the truth is that nearly all of these BCMs have no documentation or schematic to determine what they do. And ti seems a lot of the more sophisticated ones with battery balancing don't work as well as the simple ones. Balancing the cells does mean that the charging time is increased by the shifting around of charge rates. Some advertise discharge balancing as well, but in reality this is very difficult to monitor and achieve... maybe advertising hype.

Going with a good US brand is likely to cost more, but be far more reliable. In the middle of last year, I did a lot of shopping and reading about what was available on line for E-bikes. Golden Motors is one of my favorite sources, but even they seem to buy their lithium ion battery packs from another manufacturer that offers a complete package and very little explanation about what's inside. I strongly suspect that if you buy a complete LiFePO4 package from them and look inside, you will see LiMn0 cells. The 'honest retailers are selling Lithium ion and admitting that don't know which, the ambitious are claiming everything is LiFePO4 and don't actually have it.

The only cells that are certifiably LiFePO4 are the ones you buy individually and assemble yourself. The suppliers claim you absolutely must buy a matched cell set, but academic documents seem to thing there is no way to adequately match lithium cells, even if they are from the manufacturing batch run.

Buy individual cells shifts the problems of designing and building or buying a good charger on to you. And then the BCM boards that are available are rather dubious. You can buy them, but no real documentation.

I cannot emphasize too much that Lithium cells also fail from going too low in voltage. I am not certain if instantaneous dips due to stalls or huge loads will do lasting damage, but you absolutely need to have a low voltage cutoff feature included in the battery control module.

A complete drop in battery pack is only as good as the warranty and service policies of the retailer.

http://www.goldenmotor.com/phpsite/china/