LiIon 18650 Lawn Mower Battery Hack

Sorry folks as this is not a topic based on LED lights, but since there is a lot of discussion around batteries, I thought there may be some experts here who could chime in.

Here's the deal. I was thinking of current battery powered lawn mowers and the fact that LiIon technology is not quite here yet (have only seen the Bosch http://www.bosch-pt.com/productspecials/garden/li-ion/uk/en/rotak/index.htm). The rest - are all led acid and I was wondering if it would be possible to create a 24V/36V/48V LiIon battery based on 18650's to replace those in the existing led acid types. More specifically, has anyone come across specs to create the battery setup (including wiring, protection and charger) for this size of battery? I know that I could just wait for the Bosch or newer models, but that would take all the fun out of the hack in me...

Some random thoughts:
-given the size of the battery compartments, it should be possible to wire up a number of 18650's in paralell / series configuration to get 36V with enough amperage to last. If you look at the Bosch, you can see that they have added a heat sink to the battery case as well. I can imagine that these batteries would get pretty hot.

deejayspinz said:

Sorry folks as this is not a topic based on LED lights, but since there is a lot of discussion around batteries, I thought there may be some experts here who could chime in

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You are right that it doesn't belong in the LED section, but it doesn't belong in the General section either... It belongs in the BATTERIES section. I'm moving it there now.

See here for some ideas:
http://www.batteryspace.com/index.asp?PageAction=VIEWCATS&Category=911

Although for something like a lawn mower, I would look at LiFePO4 batteries:
http://www.batteryspace.com/index.asp?PageAction=VIEWCATS&Category=1440

Lithium Iron Phosphate (LiFePO4, LFE) is a new generation Li-Ion rechargeable battery for high power applications, such as EV car , Power Tool and RC hobby. LFP cells feature high discharging current, non explosive, long cycle life ( >2000 ), but its energy density is lower than normal Li-Ion cell (Li-Co) (but higher than NiMH cell). LFP cell has a 3.2V nominal working voltage and shall be cut-off at 3.6-3.8V per cell during charging. LFP battery has the lowest cost considering its long cycle life.

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One easy way is to build your battery pack using series/parallel combinations of these:
http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=5028

I thought the only disadvantage of lead-acid was the weight, don't they still provide the best cranking amps? Although I guess cost-effectiveness might not apply in this sort of project.

@rmteo, thx for the link. Wow, did not know they would be so expensive. May just have to wait for Bosch to come to Canada with their LiIon mower.

Re: LiFePo4

Yes, they are expensive when you look at the price in isolation. However, when you take cycle life into account, LiFePO4 is typically 15%-25% the cost of lead acid. The only other chemistry that is less is NiCD - everything else is more with LiIon being among the most expensive at 150-200% that of Lead Acid (and about 10x that of LiFePO4). There are also safety concerns to take into account with LiIon.

Hello DJspinz

That Bosch li-ion lawnmower looks like a great product, thanks for the link. I like the video; the lady drinking Gatorade really cracks me up

As for the battery pack, I guess you could use the 36V nanotech li-ion that the Dewalt power tools use. They have greater power capability, longer shelf life and can withstand more abuse than regular li-ion. I'm not sure if the capacity will be high enough but you can always parallel 2 packs.

Only problem is they're not cheap so as you say, you may be better off waiting for the Bosch.

I love A123 Systems LiFePO4 cells both the 26650 /2300mAh a and the 18650 / 1100 mAh ones. I have been using them for well over 2 years have thousands and thoustands of RC flights using them. Between testing,flying and running trucks I most likely have well over 10,000 charge / dischare cycles on my packs in total. Some packs have nearly 500 cycles on them ,a bunch have 300 plus and many more have 100 to 300 cycles on them. In the RC community I am perty much the A123 go to guy.

With all that being said to look at a chart that shows Pb>200 and LifePO4>2000 which is a 10:1 ratio in favor ot the LiFePO4 is IMO not fair.
I wonder what DOD they based thiose number on and if the used a preinum deep cycle Pb or a regular starting battery?

My 2000 Mazda truck still has the original battery in it and it is still working as good as new. On the other hand my 2001 Extreme Blazer is on it's fourth battery. What does this show? My Blazer is loaded with many devices which have parasitic drains and if it sets for a week the battery gets pulled down to 12 V or so which is very bad for itand would just as bad if not worse foer a LiFePO4.

Based on over 45 years using / testing rechargable batteries of nearly every typs I have found that the care they receive has a major impact on the service they deliver.

PS I also use LiFePO4 cells in a couple of my MagLites which have I have converted to LED ,one with a blazing SSC P7-C rated at 900 lumens.