Virtual alternator delete.

[redpoint5]

The other thread finally pushed me to forgo sleep in exchange for monkeying with a car I hardly drive.

I've got my Y harness wired from the battery under the hood, through the firewall, and into my glove box. The resting voltage of my Pb battery was 12.2v, and the alternator seemed to want to keep it at 14.1v. Adding in the LiPo battery only increased voltage about 0.1v, but then I haven't charged it yet.

I'll see if idle fuel consumption drops when running the LiPo... and I need to wire in a fuse in there somewhere.

[teoman]

My caps are in Germany at the moment. Waiting for them but it will take another 2 months.

I have a 6kWh lithium ion battery and I intend on using with a boost converter to feed the caps.

Alternator should be virtually deleted using this method if the cars battery management ECU doesnt throw a fit.

[redpoint5]

My LiPo pack has a resting voltage of 16.8v. It took a 3.5Ah charge last night (rated to 5Ah).

My 6s supercap bank has a max voltage rating of 16.2v, so I'll have to figure something out. Maybe simply hooking up the battery to the vehicle will drive the voltage down to ~16v. Or I could forgo the caps altogether since my 60C rated LiPo can output 300A. I've measured my car at 290A to start. I already have a 300A breaker.

The TSX has a parasitic drain of 21.5mA, so my 5000mA battery should go 9.5 days until dead. I'll need to plug in a battery maintainer if I eliminate the Pb battery since I go more than a week between driving the car. I'll also need to purchase a 2nd battery so I can swap them in and out.

[Daox]

I think Luno had a great idea where he only charged his pack to 4V per cell. This does cost you ~15% capacity loss, but if it really increases cycle life that much it sounds worth it.

[redpoint5]

I measured typical running draw at 14A on the TSX some time ago. That would give me about 20 min before the alternator kicks on using my 5aH battery. That discharge curve looks just about right for the alternator to kick on. I'd want it to leave about 20% charge just to prolong battery longevity. I'll have to test this out and see how low my battery goes before the alternator kicks in. Unfortunately I expect to be running about 3C discharge.

[teoman]

Thanks redpoint5 for that reference point. I would expect my audi to run similar numbers.

14A *13.2V = 185W

Roughly 1/4 HP of power.

If alternator and lead acid battery inefficiencies are taken in to account i would guesstimate that at 1/3 to 1/2 HP.

[teoman]

Daox, one should take in to consideration the voltage changes with temperature. Would not want the voltage to rise and pop the caps.

[redpoint5]

I think I can set my charger to a lower voltage as it has 3 settings for lithium ion batteries; standard, LiFePo4 (lowest voltage), and LiPo (highest voltage). If I set it for standard it may prolong the life of my battery and keep the voltage within the tolerances of my caps...

maybe I'll get some time tonight to actually test some things.

I'm still torn on if I should forgo the ultracaps or use them as a buffer. My little 5Ah battery is rated to start my car, but I'm not sure my wiring job is beefy enough. The 10 AWG section is, but I used dinky wire from a smoke detector connector to create the Y harness since I couldn't fit 2 sections of 10 AWG into the connector.

[Daox]

I would keep them. You want to have power to the car while you're charging the small pack.

I think I have an inexpensive option for charging a 4S pack at a reasonable rate to whatever voltage you want. Grab yourself a 12V power supply, and four adjustable dc-dc buck converters. Set those to 3.9 or whatever voltage you want. Like an RC balance charger you don't need an onboard BMS then. The 12v power supply and dc-dc converters can be had for less than $30. The ones I found will charge at 5A which is the same as my current lead acid charger and it is large enough for my use.

[redpoint5]

I probably paid around $30 for my charger, or perhaps less. My 5Ah battery was something like $20. I needed the charger anyhow for my other RC batteries, so it wasn't an additional expense for me.