Update

 The mower has been fairly consistent but I did try and push the batteries too far with bad results. One cell had swelling and was hot.

I continued to use it, but noticed a loss running time of about 6 amp hours. I finished mowing today and checked all voltages, the previously damaged cell was low and I replaced it. I had low readings on some others so I balanced them to the pack average.

I will check battery again after fully charging.

Mowing is ending but mulching leaves worked well last season so gearing up for that.

Fine tuning

 Having mowed several times I addressed a few little things. I added better connectors to battery charger and mower, the original one I pulled from my junk box was overheating so in the trash it went.

I also added a circuit to charge setup that will disconnect charger when charged and reconnect when battery is below a set value, so I can leave it and it will maintain full charge.

Another annoying item was shutting down while mowing, the seat switch was working too well, bumpy terrain causing switch to activate. After several attempts at adjusting I ended up adding a capacitor to cover short interruptions.

I now have about 1/2 seconds before shutting down, problem solved.

I clocked the speed of travel with GPS app, 7 MPH was recorded, this is also the speed I mow on the straight passes.

Temperature checks are good, so adding the fan is working to keep things cool.

Fan results and etc

 I have mowed multiple times, checking battery use and motor temperatures.

Easy to get 3/4 acre on a charge, which is either front or rear yard. Extra batteries probably wouldn’t be advantageous. If I added enough for whole yard, weight and location becomes an issue, any less seems pointless as I would need to charge to complete entire yard anyway.

I mow in the morning, plug in and mow in the evening. 

I’m not running a race, and I can live with it.

The added fan has helped, lowering temperature around 40 degrees all around. Motor is 135 at finish and adjacent batteries 104. I just have to keep the fan intake clear of grass clippings. 

The machine isn’t whisper quiet, idlers and hydraulic pump make a bit of noise, but deck noise is the major sound generator. 

Keeping things cool

 I mowed the front yard in 94 degree heat, checked the motor temperature directly after and got 170 degrees on motor and nearby batteries were 140.

I had ordered a 48 volt computer fan on eBay and decided it should be tried out for cooling. 

The fan moved a crazy amount of air, sounds like a jet engine, at one point sucking my t-shirt in and shredding it.

Not wanting to lose any digits, a guard was needed. I dug around and found an old speaker grill that fit, right down to holes lining up with fan mounts. 

I modified the grill for better air flow by removing fabric and cutting some slots.

I made a bracket for the fan and mounted it over the motor, since there was a hole in the metal I used , I installed a disable switch. 

I wired it through a fuse to come on when the drive motor runs, I will check temperature next time I mow, but I’m confident they will be less, just a matter of how much.

We’re going to need a bigger Battery

 Today I evaluated a few things, I originally thought I could get the other 32 batteries under the hood, this won’t work. A second battery set will go in a custom weight box in the front and will weigh 110 pounds, this will aid if I ever pull something.

The added batteries will almost double my run time, so I’ll be able to cut the entire yard in one shot.

The replacement battery relay arrived, so I just need to weld up the new battery box. A new fan was ordered to keep motor cooler, hopefully. 

I finally sorted out the seat switch to work the way I wanted. 

Still on the list, a good solution to charging both batteries without buying another charger, and installing the headlights.

Mowing test

 I finally got the charger in, I wired a plug and tested. I had already charged the batteries in sections so the new charger didn’t charge long and shut off. 

I wanted to do a mowing test even though I didn’t have all the batteries I wanted to install. 

I found the current decreased as time passed, perhaps the grease in spindles became softened with heat.

I mowed for about 40 minutes, probably a bit more than 1 acre. Power use was 78 amps,  about 3850 watts. This tells me my batteries have about 80% capacity at full charge.

I estimate having enough for the entire yard if I add the other batteries. I did note the motor gets pretty warm, can’t leave your hand on it. The spacer to keep batteries away from motor inlet was narrowed, it may help. I may add a fan later.

Some details

 I am still waiting on the charger replacement so in the meantime trying to find places for more batteries. The original plan was 2 sets of smaller batteries in parallel as bank 2. I now see they will not all fit as planned over the bank one set. I may build a box for front or rear to house some batteries. 

I am also waiting on spring for the seat, so my seat switch will work properly. 

I designed the electric interlocking to mimic the gas operation, key on, PTO has to be off, brake on, and seat switch on to “start”. When running, leaving seat or turning off key will stop motor and startup must be repeated. Safe from runaway mower from just turning it on.

I have some new led headlights to install as well

Original goal was proof of concept, combined with a backup for the gas mower. It may need a charge in between to complete yard but I figured that in.