Replace your car battery with capacitors!

[ECONORAM]

Do you just need to wait a few seconds after switching the key to on to let the caps build up, before you move it to start? Or is that the issue? Would that prevent the voltage sag?

[oldtamiyaphile]

OK, so I've been watching my voltage lately and it turns out my issue was simply too much EOC. The voltage dip is gone but my MPG has taken a big hit. Solar panel will be here next week so that should solve all.

The voltage still takes a dip to below 12V when bump starting though which I find a bit surprising.

[Enki]

Originally Posted by ECONORAM

Do you just need to wait a few seconds after switching the key to on to let the caps build up, before you move it to start? Or is that the issue? Would that prevent the voltage sag?

Think of capacitors like compressed air tanks for electricity. There's no waiting to use their contents, and as they are used, their pressure (voltage) drops linearly. It would be better to start the vehicle quickly so they don't drain too much.

Originally Posted by oldtamiyaphile

OK, so I've been watching my voltage lately and it turns out my issue was simply too much EOC. The voltage dip is gone but my MPG has taken a big hit. Solar panel will be here next week so that should solve all.

The voltage still takes a dip to below 12V when bump starting though which I find a bit surprising.

If you mean bank of 350 farad caps, I don't really find that surprising. In series, six of them would total 58.33 farads of capacitance, giving you an amperage dump of 233.32 amps (from 14 to 10 volts drop). That isn't much.

The stumble could be from any number of things, like there not being enough voltage to excite the alternator immediately. I'd recommend testing with a larger bank of 650s (108.3 farad effective, 433.2 amps capacitance), or adding a second bank of 350s (which should halve voltage drop).

[oldtamiyaphile]

Originally Posted by Enki

The stumble could be from any number of things, like there not being enough voltage to excite the alternator immediately.

It is indeed this. The alt is ECU controlled and doesn't fire for about 5 seconds after a bump (or key) start, what was confusing me is the big drop from firing injectors and plugs. The 100W solar panel should fix all my issues though.

[oldtamiyaphile]

So my problems are still not over. I fitted the solar panel in a big hurry after work yesterday and this morning got in the car reading 14.2V, started it, and big stumble (the kind I normally get if it's been sitting for a few days).

Could my supercap wires be too small? The biggest I had was 8GA.

[Enki]

I'm not really sure what your goal was with the solar panel, but they aren't exactly going to flash fill the caps during a start.

[oldtamiyaphile]

Since the problem only exists after being parked overnight, and gets worse if left longer, I was hoping increasing the initial voltage would work.

I'm wondering if the 8GA wires are too small for the cap to supply enough amps to crank the engine, but big enough to suck current away from the coils just after cranking.

[Enki]

It could just be that cold starts take a bunch more power than warm ones (morning vs afternoon cold starts)...?

[redpoint5]

8 AWG is certainly large enough, assuming your leads aren't extremely long.

Your issue is strange because I have never had caps cause worse performance. I suspect something else is going on. My motorcycle, Camry, and TSX can all start off the caps and run without issue. I've measured voltage sag as low as 6.6v while starting the TSX on caps alone, and it runs just fine after starting.

11v should be plenty for the car to run without having ignition issues. Does the car start and run properly when you put a known good battery in? I'd take your Jeep battery and see if the problem is still there.

... in other news, the 3400 farad caps are on the way. It will be about a month before I get the time to test them in my Dodge/Cummins truck, sans battery. I bought zener diodes and white LEDs and will test to see which makes for a better balance circuit.

[oldtamiyaphile]

It's a hot summer here so morning starts aren't really that cold.

The car and battery are new and had no issues prior to fitting the caps. This morning it started perfectly though so fingers crossed the ECU has 'learned' something.

I did first use the caps on the Jeep and also got a slight stumble (the battery IS weak on that one), and the caps couldn't start my 875cc Fiat, barely got a turn of the flywheel.

Beginning to suspect it's the caps themselves that are faulty, but then they seem to bench charge fine.