Can I convert a standard hybrid car to plug-in hybrid (PHEV)?
DIY PHEV - can you upgrade a standard hybrid to plug-in, perhaps in the shed at home, or are you (literally) playing with fire?
QUESTION
Tell me please, am I dreaming, or would it not be feasible, to convert a "soft hybrid" or just hybrid car to a full plug-in hybrid, by adding another battery and appropriate connections?
Series or parallel, wouldn't that at least double autonomy and offer the option of mains charge?
Or would it end up costing as much as a full EV? - John
ANSWER
Hypothetically you could do this. But it’s not a backyard job. You’re talking about a great deal of stored energy, and the potential for disaster is extremely high.
It’s a fascinating question, though, because as hybrids and EVs become more mainstream, I suspect we will see an explosion (hopefully not literally, at least very often) in aftermarket modifications and kits for the electrical side of these vehicles.
On this proposal, specifically:
Seeing as there’s no spare space in the engine bay or the sub-floor space, the battery would have to be installed in the boot, where it would be vulnerable to crash damage (which poses an extreme fire risk). You’d have to include temperature management for both charging and discharge (‘discharge’ = powertrain use, for powering the electric motor). If you don’t do this, there’s the risk of killing the battery early, and also fire/explosion.
And then there’s the high-voltage wiring and all the technical caveats for safe installation that this imposes. And the battery would have to be custom made, which would cost heaps.
To put this in perspective, a 36-volt, 5 amp-hour battery for Ryobi yard-type electrical power tools costs $299 retail at Bunnings. I’m sure they’re marking it right up, but at the same time they’re benefitting from mass production. That’s 180 watt-hours of electrical energy, or 0.18 kWh (kilowatt hours). Hold that thought.
A Hyundai Ioniq hybrid has 1.56 kWh of battery storage on board, and the PHEV version of the same car has 8.9 kWh. The difference is 7.34 kHh. It’s significant.
Let’s say you intended - conservatively - to add 5 kWh of electrical storage to your standard hybrid ‘donor’ car. At the same price per kilowatt-hour as the Ryobi battery that’s about (ballpark) 30 times the energy, so 30 times the price, or about $9000.
Jaycar Electronics will sell you 18650 Li-ion rechargeable battery cells (unprotected cells) for $12.45 as a bulk buy. They’re 9.62 Wh batteries. So you’d need 520 of them for 5 kWh - that’s about $6500. And of course you’d need to figure out how to wire them up and protect them…
You’d probably buy those individual cells cheaper, but you’d need a spot-welder for joining them up, and a bunch of additional components such as a complete heat exchanger setup, wiring, enclosure, protection circuit, thermal overload detection, etc. It’s doubtful to me you could do this on a shoestring for less than about $20,000. That’s not including your own time.
Bear in mind you can’t do this well in one hit. Nobody goes from concept to production ready in the one iteration. You’d need a prototype, then a second prototype incorporating a bunch of refinements from what you learned in prototype #1. Then - hopefully - you’d be production ready the third time. Make it $30,000 - if you can successfully re-use a bunch of components from each of the previous prototypes.
At this point it behooves me to point out that it’s cheaper just to buy the PHEV, which is about $6500 extra in the case of the Ioniq.
I also cannot overstate how easy it is to hurt yourself badly if you get this wrong. ‘Nice idea’ to ‘burns unit’ is a foreseeable pathway for this project to follow.
In choosing the donor car for this project you would also need to ensure it could run, and provide adequate motive power across a wide range of driving conditions, in ‘EV’ mode. Bear in mind that the Ioniq EV has a 40 per cent more powerful electric motor to facilitate exactly this kind of operation. Designing a bigger battery to drive a ‘Mr Puniverse’ electric motor would be another epic ‘own goal’.
You’d also need to be able to hack the donor car’s control architecture so that you avoided unpredictable feedback effects and operational conflicts - which are bound to occur with a modification that goes this deep. This is going to be very difficult without manufacturer support, which you will not get.
Then you have to failsafe the installation … so that you don’t make the news in some spectacular fashion on the way to work one day.
The resultant car is also going to be uninsurable - and you can’t just not tell your insurer you have done this because that’s a failure of your duty of disclosure, so you’ll pay your premium but be uninsured in any case…
So if you are a full-on electrical engineer with high-level electrical trade skills and a full-on prototype development workshop, you’re not dreaming. Otherwise, you are. And even if you’re not dreaming, it’s going to be cost prohibitive and the outcome - even if completely robust and functional - won’t be insurable.
