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Converting Petrol Car to battery.



  • Registered Users Posts: 436 ✭✭Girl Geraldine

    Moving a heavy brick at 10 km distance 120km/hr doesn't take more energy than moving the same brick the same distance at 30km/hr.

    there will be some increase in rolling resistance, but not huge either.

    Most of the energy shed during braking in an EV is recouped by regenerative baking, unlike in an ICE car where it is shed as waste heat.

    However, when you bring air resistance into it, going a to b is going to use a lot more energy than doing the same journey at 30km/hr.

  • Registered Users Posts: 64,355 ✭✭✭✭unkel

    @Girl Geraldine - "Moving a heavy brick at 10 km distance 120km/hr doesn't take more energy than moving the same brick the same distance at 30km/hr."

    LOL, completely wrong. Have you never heard that aerodynamic resistance quadruples when you double the speed? And you have obviously never owned an EV, because this becomes obvious instantly when you see the range drop at speed 😂 It's the reason why Nissan Leafs tend to drive at LeafSpeed on motorways (88km/h exactly). It's the same in ICE cars, but far less obvious as a typical ICE car has 10 times the amount of energy on board

    @hometruths - spot on. Potter about never going anywhere near motorway speeds and you will have a lot more range. This applies to all EVs, even the most aerodynamic ones like all Teslas. The effect is far greater again with a "brick" like a Range Rover

  • Registered Users Posts: 436 ✭✭Girl Geraldine

    if you read the second half of my post you'd see that I do know what drag is.

    Losses due to drag won't be affected by what weight brick he has in the boot. Rolling resistance, and some braking losses might increase, but areodynamic drag won't.

    D = Cd * A * .5 * r * V^2

    I don't see an "m" in there.

  • Registered Users, Subscribers Posts: 5,787 ✭✭✭hometruths

    It's sort of instinctively makes sense, hence the assumption, and my hope that I will get sufficient practical range for the purposes I wish to use the car for.

    But also why I am intrigued about chrskly's comment that weight doesn't matter as much as you might think. I'm assuming it matters a great deal! Just less so in go slow mode!

  • Registered Users Posts: 64,355 ✭✭✭✭unkel

    No he is right. It depends of course how many batteries you are going to fit, but if it is only for a short to medium range (up to say 70-100km), the car will likely end up about the same weight or even less than before the conversion

    Also, when you have fitted the battery, that doesn't mean that's set in stone. You could always change the battery or add to it. This is relatively straight forward. As opposed to motor and gearbox / controller / inverter, etc. Not so easy changing any of those around

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  • Registered Users, Subscribers Posts: 5,787 ✭✭✭hometruths

    Just watched one of Damien Maguire's videos in which he makes the point that the thinking any conversion must be small, light and aerodynamic is actually a hangover from the days when the only option was lead acid batteries. With the mass market availability of lithium batteries, this is no longer a concern, but the thinking has stuck. He mentions your car in it.

    @donalh087 it is a fairly long video, but hopefully it will give you some reassurance that converting a big old lump of a jeep is not madness.

  • Registered Users Posts: 64,355 ✭✭✭✭unkel

    He's right. Batteries are everywhere. Still not super cheap but there are loads of options. And if you are humble in your demands for range for the converted ICE car, they don't have to be that expensive either. Making good progress on the Red Arrow, have already booked it in for the NCT, one more small job to do for it

  • Registered Users Posts: 64,355 ✭✭✭✭unkel

    Here's the link to my car, I updated it today with some recent work done:

  • Registered Users Posts: 436 ✭✭Girl Geraldine

    Do the NCT and/or insurers require an engineers report confirming that the conversion is done properly?

    I mean you or I, with enough effort and money applied, could make a conversion car work, but we'd not be qualified auto electricians or welders. There would be no reasonable guarantee that it has been done properly, ie that any welding is good enough, and that electrical equipment is properly specced, installed and prgrammed.

    Also, in these conversions, how do ye manage the brake vacuum servo? Is there an electrically powered vacuum pump?

  • Registered Users, Subscribers Posts: 5,787 ✭✭✭hometruths

    In order for it to be official registered as an EV, the conversion needs to be signed off by an SQI. And as far as I am aware the official classification satisfies the NCT inspection, though obviously if they see something dangerous they will fail it.

    For insurance it is the same - an SQI has to check it and sign it off.

    You can run a pump off 12v battery I understand.

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  • Registered Users Posts: 6,439 ✭✭✭zg3409

    Yes, you need an engineer's report to keep insurance and NCT happy and possibly to reclassify vehicle fuel type.

    For power steering some makes of cars use electric hydraulic pumps so you can get the right part from a scrap yard.

    Some cars use electric power steering already such as Mazda rx8.

    Similar for power brakes etc.

    Similar for Aircon although most cheap conversions don't bother.

    In terms of range at high speed, speed has a massive impact on range mostly due to pushing air out of the way. A low speed EV has very little air problem and driving on a flat straight road at a constant speed uses little energy. Take same car at high speed with head wind and batteries go down quickly. Add in a few hills, slowing down and speeding up a huge tank, winter heating, summer Aircon, and batteries give less range when winter cold means ranges in mild weather at low speed are very high, but if you drive like you stole it range will drop rapidly. Most suppliers just put in massive batteries, fast charging, sleek body styling, heat pumps for efficient Aircon and a range display (guess o meter) that reacts to driving style to update and warn driver to stop and charge long before car actually conks out.

  • Registered Users Posts: 3 _chrskly_

    As others here (and Damien) point out, the weight thing is a hold over from earlier days of conversions, where lead-acid batteries were the only option. Lead-acid batteries cannot deliver enough current to accellerate a vehicle to motorway speeds well enough. So the conversion community at the time got overly fixated on the idea of making cars lighter and more aerodynamic. This notion has persisted in some circles despite the fact that battery technology is much better now.

    As for how weight relates to energy efficiency, my understanding is that the weight of an EV only really factors in when you're accelerating. The difference in energy required to maintain a constant speed between a 'light' car and a 'heavy' car (where you're holding the aerodynamic resistance constant) is minor. Especially compared to the 'cost' of aerodynamic resistance on the vehicle in the overall energy efficiency of the car. So, basically, unless you're building a track car then weight matters less. It's not that weight doesn't matter at all, it's just that the idea that you can't convert a heavy car and get reasonable mileage out of it is nonsense.

    Also, it is advised to keep the weight of the converted vehicle at or below the original weight. This is a safety/certification consideration.

    For vacuum/hydraulic stuff, there are lots of options. There are lots of cars that have electrically-driven power steering/brakes. The Opel Zafira vacuum pump, for example, is popuar and cheap (although noisy) plug and play job.

  • Registered Users Posts: 64,355 ✭✭✭✭unkel

    It's noisy alright 😂

    I'd be near certain that the "Red Arrow" BMW E36 318tds is significantly lighter as an EV than it was as a diesel car with a full tank.