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beem0 09-16-09 04:48 PM

I actually have built up a Simplicity to be electric. I'm very happy with it, but just struggling with knowing if I'm hurting the batteries and also charging them correctly. What voltage levels do you go down to for 50% DOD? Under load or no load?

I'd recommend some batteries in the back for increased traction and less steering effort. I'm running 48V and have two in front and two in back.

Daox 09-16-09 05:05 PM

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Ah, great! Perhaps you could start a thread that explains your conversion. I know I'd be very interested. :)

Anyway, for a DOD chart, I would use this (found here).

So, if you're measuring a 48V system, 42V would be your absolute minimum you'd ever want to go. 50% dod would be down to 48.2V.

If you are using unbalanced batteries, you really want a meter like the link I posted before that monitors each battery. However, if your batteries are pretty well matched, you can just use a regular voltmeter.

beem0 09-16-09 05:40 PM

Great website. I've seen similar tables, but where I stuggle is the load vs no load (aka open circuit) question. When I start the motor, the voltage will drop say from 12.7 to 12.2 yet the bats should be fully charged. It would be nice to know the state of charge while mowing, but seems to be difficult. I think I might just measure the no-load voltage after mowing for a half hour. If it is at say 50% I will use the loaded voltage measurement i had at that half hour time as a cut off.

I have a hydrostic tranmission, so I'm probably pulling more current then you. I went with Interstate SRM-29's. They are very heavy, but two in front and two in back I can't even tell. I think it actually handles better then stock and definatly has better traction!


Daox 09-16-09 06:03 PM

Unfortunately, you do check your battery voltage for SOC under load. The point being, you never want the voltage to sag under 10.5V or you risk damaging them. The voltage sag really does tend to screw things up when you're putting a big load on the batteries though.

Voltage really isn't the best way of measuring SOC though. The only way to really know is to use a specific gravity tester (which only works on flooded batteries), but thats just not practical while you're using the mower.

I did look up your batteries and they don't have an Ah rating on them. I would double check and make sure that they aren't a hybrid battery (aka marine starter). They are a mix between a starting battery and a true deep cycle battery. Marine starting batteries aren't built for constant deep cycling like full blown deep cycle battery is and definitly won't last as long.

beem0 09-16-09 06:44 PM

Oh man, I hope these are true deep cycles. Interstate told me these are what can use and have a rating of 126Ah (using 20 hr method). I was looking at AGM and Gel, but went with just these flooded lead-acid for cost. These seem to work good, ran a half hour mowing and no signs of slowing. I have a 6000W motor.....can't even slow it down going up hill. I pull around 70amps mowing at a good speed, and can hit up to 120amps going up hill. I really need to find a way to lower the current draw.....that is my next task after fully understanding the batteries!

Thanks for the help!

Daox 09-16-09 08:53 PM

Well, if they are rated for 126Ah they're likely true deep cycles, and if they recommended them for your application I'd be even more sure. That is also a really high rating for a 12V battery.

I will be taking your advise about positioning the batteries in the back side (at least two of them). With the batteries as they are in the pictures I do sometimes have some problems with traction. However, I think that mainly stems from the mower's ability to turn pretty sharply. It even turns far enough to wedge the front tire under the front foot rests.

beem0 09-20-09 10:49 AM

I went and bought a hydrometer and it shows my batteries are in better shape then what the voltage measurements reflect. Based on that I mowed for about 30-40 minutes and only went down about 50% DOD. I think that is pretty good!

Daox 09-21-09 07:32 AM

Wow, thats great news. Sounds like you got yourself some great batteries there. I might have to look into getting some of those. :)

beem0 09-21-09 09:52 AM

I'm now trying to understand how much life I can get out of them. I read you can get anywhere from 300-500 cycles out of deep cycle bats, but is that over a certain amount of time? I mean if I mow my lawn 30 times a year, does that mean i can get 10+ years out of them?!?! That is hard to believe, but would be awesome!

Daox 09-21-09 10:14 AM

I think that might be close to possible. The guy I called up last week said the batteries he pulls out of floor cleaners are about seven years old. If proper maintenance is kept up on them, I don't see why you should expect anything less.

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