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A local inventor persuaded me to put a 12 volt NiMH battery into my 2001 Gen 1 insight - a bolt-in replacement when my 12v lead-acid battery wore out.
It's made of 30 heavy-duty NiMH D cells he purchased online, wired as 3 strings (in parallel) of 10 cells each (in series), so its voltage is almost exactly the same as a 12 lead-acid battery.
The cells are connected with about 10-gauge wire, and the joints are all soldered (I know the battery manufacturers don't recommend that). It's all in a plexiglass case with stainless steel bolts as terminals to connect to the car. It's quite light compared to a lead-acid one, but I haven't weighed it.
It cost about $300 but it was fun to try to save a bit of weight, and it is still working fine after 16 months and about 8,000 km.
I don't have a DC 'ring' ammeter to put on the cable going into it to measure how much current it draws when it is fully charged - because the voltage doesn't rise when full, the DC-DC converter can't detect that and slow down the flow.
He says that it should be good for 180 cranking amps, but I've never tested that with my new IMA battery always starting the ICE engine. It never gets below -10 Celsius here (about +15 F) so I'm not worried about low-temperature performance.
Here is his explanation of the voltage characteristics:
"Constant voltage charging is usually done with too high a voltage [for NiMH batteries of 10 cells in series].
I've done some tests and 13.75 to 13.90 volts is not only "okay" but IDEAL continuous voltage - they draw trivial current once they're charged to stay at those levels. The standard vehicle charging system is fortuitously 13.8 volts. So it happens that NiMHs are actually a better fit for vehicles than lead-acid - the voltage stays above 13 volts with the engine off, so headlights don't dim, etc, and you can turn off the engine at long lights, use lights and radio with the car off, etc, and save gas without worrying about the effect on the battery.
At 14.00 volts up, they keep drawing significant current once they're charged. The usual 14.2 volts is definitely overcharging if left on once they're charged."
There is no internal circuitry to balance the charges in the individual D cells - it's just all wired together, so presumably it will start to lose capacity as the cells age. I've no idea how long that will take.
More about this in the inventor's newsletter here: (see Car Battery Project)
Turquoise Energy Newsletter #36
I have a fuzzy photo of the battery attached.
It's made of 30 heavy-duty NiMH D cells he purchased online, wired as 3 strings (in parallel) of 10 cells each (in series), so its voltage is almost exactly the same as a 12 lead-acid battery.
The cells are connected with about 10-gauge wire, and the joints are all soldered (I know the battery manufacturers don't recommend that). It's all in a plexiglass case with stainless steel bolts as terminals to connect to the car. It's quite light compared to a lead-acid one, but I haven't weighed it.
It cost about $300 but it was fun to try to save a bit of weight, and it is still working fine after 16 months and about 8,000 km.
I don't have a DC 'ring' ammeter to put on the cable going into it to measure how much current it draws when it is fully charged - because the voltage doesn't rise when full, the DC-DC converter can't detect that and slow down the flow.
He says that it should be good for 180 cranking amps, but I've never tested that with my new IMA battery always starting the ICE engine. It never gets below -10 Celsius here (about +15 F) so I'm not worried about low-temperature performance.
Here is his explanation of the voltage characteristics:
"Constant voltage charging is usually done with too high a voltage [for NiMH batteries of 10 cells in series].
I've done some tests and 13.75 to 13.90 volts is not only "okay" but IDEAL continuous voltage - they draw trivial current once they're charged to stay at those levels. The standard vehicle charging system is fortuitously 13.8 volts. So it happens that NiMHs are actually a better fit for vehicles than lead-acid - the voltage stays above 13 volts with the engine off, so headlights don't dim, etc, and you can turn off the engine at long lights, use lights and radio with the car off, etc, and save gas without worrying about the effect on the battery.
At 14.00 volts up, they keep drawing significant current once they're charged. The usual 14.2 volts is definitely overcharging if left on once they're charged."
There is no internal circuitry to balance the charges in the individual D cells - it's just all wired together, so presumably it will start to lose capacity as the cells age. I've no idea how long that will take.
More about this in the inventor's newsletter here: (see Car Battery Project)
Turquoise Energy Newsletter #36
I have a fuzzy photo of the battery attached.
30Ah is roughly the same capacity as the stock lead acid battery.
