Using a Lawn Tractor Battery as a whole home battery backup

byteharmony · Oct 13, 2022

Vigo said:
So when i first went off grid the only things i needed to run overnight were a small window ac and my fridge. I had a largeish 12v system that was only ever supposed to be a backup, and when i started piecing my 48v system together the very first 48v pack was just 4x group 27 marine batteries from walmart (~$370). That was not truly sufficient so i was supplementing them with a tiny 700w inverter generator running 2-300w of charging. Was very quiet, burned ~1 gal gas a night, ran my room ac, ran my fridge. Now 1 gal gas a night is still crap because thats $90/month JUST to power the nighttime hours! But it was a tenable stopgap and i probably didn’t even run it for a whole month anyway. Next step was actually even more relevant as i bought 4 slightly large group 29 batteries, so i could move the 4 group 27s into my golf cart (where they still live) and then parallel that to the house whenever i wasnt using it. I actually ran off that group of 8 batteries (half of it a golf cart) with some small 100-200w overnight supplemental charging from my slightly larger 12v system, for a good long while until i came into 24x used large 6v deep cycles Rolls FLAs that i semi-rehabbed and now makes up the majority of my 48v system. I still parallel the golf cart directly to it for charging. i just spot checked a few cells SG on the cart and while theyre still lower than the main pack after sitting hooked up all day, its not in a range where i’m killing them either, so it’s ‘working’ as far as i care.

If it were done with slightly more effort i see no reason not to locate a significant chunk of your battery capacity in vehicles. Ove done that on my 12v system and have cars trucks tractor rv riding mower etc all hooked to it.

Ive considered converting my small skid steer to electric as well, but it would probably be a 100-200v system. I have a 52hp brushless motor and controller, dc dc converter and charger from a 1993 electric car i parted out..

Thx for sharing your experience! Makes me feel better about investing time in my future plans.

I'm thinking the same thing regarding the one problem we're seeing, the higher voltage for some larger devices.

I found these two threads interesting:

Two 48V banks in series for 96V with Off-The-Shelf Equipment

I am planning a solar/electric powered boat. The plan was a pair of 6kW arrays, each running through a EG4 6500W inverter/charger to a pair of 40kWh, 48V banks. The problem is the 55hp, AC-20 motor is to be run at 96V. So, I THOUGHT I could run the two 48V banks in series BUT EG4 support says...

diysolarforum.com

96v boat upgrade

This is my current project. I had built this boat for my specific needs of coastal cruising. It is 35', trailer able, beachable, light, fast (35+kts) and has less than 8' bridge clearance. It did everything it was designed to do. Now I want to go farther (maybe the great loop) and tired of...

diysolarforum.com

I think for my boat project, I'll stick with 48v. Speed is not a goal.

If a land project requires higher voltage I like the idea of series 48v. If I didn't use it all that often, I could just use the same connectors all the APC devices use: JST I think.

Until I learned more, just unplug each battery and plug it into a JST that makes them parallel with the appropriate fuses.

Maybe switch to a knife switch and single JST that has fuses in the toy after I see how well it works.

More batteries = less load on each cell, longer life, lower heat loss.... man who smiles more.

(Is Thomas Edison enjoying seeing the DC power get some market back from Tesla's AC?)

Vigo · Oct 13, 2022

Its possible with three contactors to switch two battery banks from parallel to series but you would also have to isolate them from the 48 V loads at the same time. 48v sources you could just add a diode or they might already have one. Or, if you built or had a large ‘balancer’ you could take the 96 V from both 48 V banks, simultaneously run the 48 V loads from only one of the two banks and then let your big active balancer fix it later. obviously depends on basically all the details but it’s possible.. ?

byteharmony · Oct 14, 2022

Vigo said:
Its possible with three contactors to switch two battery banks from parallel to series but you would also have to isolate them from the 48 V loads at the same time. 48v sources you could just add a diode or they might already have one. Or, if you built or had a large ‘balancer’ you could take the 96 V from both 48 V banks, simultaneously run the 48 V loads from only one of the two banks and then let your big active balancer fix it later. obviously depends on basically all the details but it’s possible.. ?

In the case of most / all of these toys, it would be rare that they'd need 96v, but if they did I would not have them in use while charging. The single switch to go from parallel (charging) to series (discharging) would be great. I would need either 2 bms units or I'd need to connect the bms balance wires when charging... I'd guess I'd go with 2 bms units given the # of cells / wires / chance for an error.... etc.

byteharmony · Oct 17, 2022

New idea using wire impedance (resistance) for easier / less complicated connections. @timselectric - While this may be less efficient than AC for the initial charge (MAYBE) I think it's better in all the other ways. Maybe perfect for you:

using wire length and awg as charging and discharging limiter

Question: Is there any reason this is a bad idea? Inspired by this guys recycled AC Panel: Does anyone have any experience with limiting charge current and discharge current by wire gauge and length? An example of this is using 14 AWG wire to directly connect two different LIFEPO4 batteries...

diysolarforum.com

timselectric · Oct 17, 2022

byteharmony said:
New idea using wire impedance (resistance) for easier / less complicated connections. @timselectric - While this may be less efficient than AC for the initial charge (MAYBE) I think it's better in all the other ways. Maybe perfect for you:

using wire length and awg as charging and discharging limiter

Question: Is there any reason this is a bad idea? Inspired by this guys recycled AC Panel: Does anyone have any experience with limiting charge current and discharge current by wire gauge and length? An example of this is using 14 AWG wire to directly connect two different LIFEPO4 batteries...

diysolarforum.com

I don't want to limit my charge or discharge.
When I put the solar on my garage, the circuits will be ran back to the power room in the house. I just think that it is better to keep everything together, for efficiency. There are days when I don't use any power in the garage. (Other than the always loads) so I don't want to waste the possible production of those days.
I'd rather put it into the main battery bank.

Vigo · Oct 17, 2022

I have used a set of automotive jumper cables in 3 different ways (single conductor, two in series, two in parallel) to add resistance to the ground clamp of a cheap welder to 'turn it down' for sheetmetal. But i only did that because the onboard controls sucked. I think that while it's possible to do it just points to a lack of 'better' controls implemented.

Using a Lawn Tractor Battery as a whole home battery backup

Is using a battery system in a lawn tractor a bad idea?

Yes

No

Maybe

byteharmony

Sunny side up please.

Two 48V banks in series for 96V with Off-The-Shelf Equipment

96v boat upgrade

Vigo

Solar Addict

byteharmony

Sunny side up please.

byteharmony

Sunny side up please.

using wire length and awg as charging and discharging limiter

timselectric

If I can do it, you can do it.

using wire length and awg as charging and discharging limiter

Vigo

Solar Addict

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