It’s been a little while since I’ve posted anything here, but there is good reason – I’ve been haunting the forums of DIYElectricCar.com. I do still have some thoughts to share here (And which may be posted on their forums also).
“Series” Hybrids. These differ from “Parallel” hybrids like the Prius in that you have a generator hooked to the batteries, which is then hooked to the drive wheels, rather than (as the Prius has) both motors (ICE and electric) hooked to the wheels with some kind of fancy balancing transmission system.
Sounds easy, right? Grab an electric-start genny, throw it in the trunk of the car, make a quick-and-dirty bridge rectifier, and when the batteries get low just fire up the genny to recharge them as you go. Unfortunately, it’s not quite that easy (When is it ever that easy?). You have to get the voltage requirements and power load worked out properly too. For instance, the above won’t work if you’re not running a 120v battery pack. Your rectifier will give you a 120v (or 240v) feed, which will be too high/too low for your batteries and damage them, or not help in any meaningful way.
Of course, the other potential problem is that to recharge a cell you have to supply it more power than it runs at. So, to recharge a 12v lead-acid cell, you have to pump in 13.8v (Or there abouts). If you’re supplying higher voltages to your batteries, your drive motor is more likely to run directly from your generator, as there is more power available from there, and the batteries won’t see (much) charge. Some might consider this not an issue. If the motor needs the power, it would be draining it from the batteries anyway, and during the “lean” load periods the batteries will still be getting their charge.
A solution would be to run two battery packs in parallel, and when the time comes to start the charging system, switch one of the packs from “Run” to “Charge”, reducing the batteries driving the motor to one pack (And so halving the runtime) and charging the other, and switching between the two as needed. So, for instance, when the pair of packs reach 75% DoD, disconnect one pack and start charging. When the remaining pack reaches 70% (The danger zone for most battery packs), or the charging pack reaches 100%, switch packs so the freshly-charged pack drives the motor while the depleted pack now gets charged from the genny. The issue here would then be balancing the packs so they can be used in parallel once again. Of course, you could always just hook up the packs in parallel again and let them balance each other out, but that’s something that’s not so good for the batteries.
Any thoughts? Suggestions? Comments?
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