A few figures

When I first looked at converting I was looking at a Ford Courier Xtra-Cab, this is because it has a high GVM rating and has seating for four. The high GVM would allow me to carry 24 6-Volt lead acid batteries with a high ampere-hour (Ah) of 256Ah. 24 batteries would give me a motor voltage of 144 volts (6V x 24 batt = 144V). Unfortunately at 31kg per battery that means 744kg of extra weight, hence the requirement for a high GVM. If I exceed the GVM then I will need to upgrade axles, suspension, brakes etc. In short, becomes a bit of a nightmare so 24 batteries would be max weight for GVM. One problem with lead acid batteries is something called the Peukert factor, this is when the batteries are discharged quickly it reduces its effective capacity. This will be different for different batteries, usually in the order 1.8 PF. So for a bank of batteries that have a capacity of 256Ah, they would have an effective capacity of 256Ah ÷ 1.8PF = 142Ah. But it doesn’t stop there, one shouldn’t discharge the batteries past 80% so now you get 142Ah x 0.8 = 113.6Ah. Now it takes about (rough figure) 120 watts to drive a 1 tonne vehicle 1km, this vehicle will have a GVM of 2.4T. That makes it 120W x 2.4T = 288W/km. If I have 113.6AH x 144V = 16358.4W of usable power at 288W/km then 16358.4W ÷ 288W = 56.8km. Not a hell of a lot of kilometers between charges! Lead acid will last about five years if you look after them. The batteries are about $260ea, so about $6240 for the battery bank.

Looking at the RX7 with its low GVM I wouldn’t get many kms per charge on lead acid as the weight would eat into the amount of batteries I could carry. The other solution would be to go to Lithium Iron Phosphate (LiFePo4 or LFP) batteries. The cheapest on the market available are from Thundersky in China (this is the picture on the left), they have a very bad rep a few years back due to a bad batch but have since improved the manufacturing process and I haven’t heard anything bad since. They come in 3V batteries so I would need 48 of them to get 144V, each battery weighs 5.6kg so 5.6kg x 48 = 268.8kg. A lot less than lead acid and also physically smaller. So how many kilometers per charge can I get?

I’m looking at 160Ah at 144V = 23040W. Again I won’t be discharging no more than 80% so 23040W x 0.8 = 18432W capacity. The good thing with LFP is that the Peukert factor is near 1 so there is no reducing the Ah rating. The GVM is about 1.4T (I’m guessing here and have yet to get a firm figure) so 120W/km x 1.4T = 168W/km. So how many kilometers between charges? 18432W ÷ 168W = 109.7km. The Thunderskys will take at least 2000 charges, so if I was to do 100km/charge I would get 200,000km on the battery banks life of 5.5 years.

So what is the cost of running the vehicle? The Thunderskys are about $239/battery at 48 batteries = $11472 …… yikes! Add to that the cost of electricity, the charger will charge at a rate of about 2000W/hr or 2kw/hr for 5-8 hours … say 8 hours. I don’t have a cheap tariff so my power is $0.14c/kwhr so $0.14 x 2kw x 8 hours = $2.24/charge. Lets extend that over 5.5 years … $2.24 x 364 days x 5.5 years = $4484.48 but we’ll add 20% inflation ($896.90) to that which makes it $5381.38. So total cost for 5.5 years is $5381.38 + $11472 = $16853.38 for 200,000kms. That is a cost of $16853.38 ÷ 200,000km = $0.0843/km … say 8.5 cents\km. Using current fuel prices of $1.40/ltr we have a Mazda 3 which runs at 12 cents/km or $24,000/200,000kms and we also have a Pajero which runs at 21.7 cents/km or $43,400/200,000kms. I think the maths speak for themselves even with a 20% increase, I haven’t even looked at any petrol price hikes which would make the figures even more interesting. It is a big outlay for the batteries but I look at as pre paying for fuel. It will be sooo good to drive past petrol stations with rising prices. Also the price of LFP batteries appear to be reducing, this is one of the reasons I’ll purchase the batteries last. Another saving will be that I will only periodically need to change the oil in the diff and gearbox, there will be no need for regular engine oil changes, filters etc. Did I mention the positive effect on the environment? An electric vehicle will reduce pollution by about 20 tonnes of greenhouse gases per year!