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Electric Tractor Project Overview (Plan A)

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    1967 David Brown 880 Selectamatic Can we make it an eTractor? Yes, we can (well, we will see 😃)  After completing other electric scooter projects (see Electric Joker ) I wanted to do something more challenging. Thought about converting a car, but there's way too many requirements to complete a road legal conversion. So, why not a tractor for use on our lifestyle block? Why did I choose a David Brown tractor for my Electric Tractor project? Mainly because I wanted a tractor that didn't rely on the petrol/diesel engine (ICE - internal combustion engine) to connect the front frame and wheels to the rest of the tractor. Looked around for a few potential options - Fergies and Fords were out, but David Browns seemed like a good option. Looking at the David Brown 880 my initial plan (Plan A) was:   The David Brown 880 picture below shows you the tractor and how the major engine and transmission components are laid out. And, the following gives an exploded view of thos
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Awesome New Battery

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NZ Lithium 160Ah LiFePO4 battery pack installed in eTractor
New Battery Pack Installed

The new 160Ah LiFePO4 battery pack and charger has arrived and now been installed. And..., the results are awesome!

After discussions with Jesse at NZ Lithium I decided on a 77V 160Ah 24S (24x 3.2V 160Ah cells in series) LiFePO4 battery pack with 200A Battery Management System (BMS) and a 20A charger.

 

LiFePO4 battery temporarily installed in electric tractor.

For the first lot of tests with the new battery I just strapped in the battery temporarily. The battery arrived with 91% State of Charge (SOC) and running the tractor for about 1/2 an hour on the first run - just taking it easy (about 30A avg) - then for about 90 mins on a second run with moderate loads (but a couple of times at high speed - peaking 110A) and the battery only dropped to 73% SOC. Nice!

I was a bit worried as the cell voltages did slump a bit - from 3.28V at the start to 2.97V at the end of the testing - which would suggest a lower SOC.

Screenshot of JK BMS app for LiFePO4 battery pack.
JK BMS screenshot showing LiFePO4 battery pack under load

Battery readings at start of test         Battery readings under load            Battery readings after 44min test

 

However, after further testing I worked out that the BMS's reported battery SOC ("Remain Battery") is based on the Ah used, not battery voltage as I thought. The BMS's Ah used matches pretty much what the Cycle Analyst displays say too, so I'm confident that the BMS is accurate.

I also found out from Jesse that the battery voltage slumps more when the battery is cold - the numbers I mentioned in the first tests above were with a starting battery temp of 8 deg C. Testing with the battery temp at 15 deg C and above showed much healthier numbers. Will see how my winter use goes - I might need to get an electric heat wrap sorted for it 😁.

Anyway, the battery is now fitted with a frame to the tractor (took the opportunity to clean and paint the front of the tractor too):

Battery mounting frame ready on eTractor
Battery mounting frame ready (and front of tractor painted)

Battery installed and eTractor ready
Battery fitted and bonnet back on

So, except for a bunch of tidying up (cosmetic tweaks), the tractor is pretty much all ready for service:

Electric Tractor ready for regular use.
Yes, I am pleased with the outcome 😃

So, keep an eye out for my next and last post where I provide a wrap up of further testing, and I'll share the total project costs...




Location: Vaile Road, Newstead, HamiltonZealand

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