Warm air intake

[Magician]

Or maybe some batteries from a salvaged hybrid....

[Stubby79]

Originally Posted by cRiPpLe_rOoStEr

Is there alternative other than a marine battery that you would consider to try? What about a lithium battery?

If you went with LiFePO4, you would have a "nominal" voltage of 12.8v with 4 cells, and it should maintain said voltage (or slightly higher) from charged right up until it's dead. Rather than dropping steadily from 12.6v until it's dead at 10v with a lead-acid.

Cells are ~$1.20 per amp-hour, so a 100ah battery with 4 cells in it would be nearly $500.

They would need some control circuitry on them to protect them from over or under charging and to keep them balanced. Under $50 will do the job. You'd be fine charging it without an alternator, but you would have to figure out how to make it work properly with one, if you did. Unless the control circuit is deigned for it.

You'd get a lot more cycles out of it then you would for a lead-acid, so it would end up cheaper in the long run.

OTOH, basic LiFePO4 aren't good below freezing temps, so come winter, you'd need a battery warmer. Or a different chemistry. There is a slightly different chemistry that is basically the same, other than weighing a bit more for the same capacity and it's good for -20c or so.

My original thought was to use a regular lead-acid deep-cycle and throw in a buck booster (readily available on ebay for like $20) and some diodes, so that the ECU/ignition always got a set voltage (13v? 14v?) in spite of what the rest of the system voltage was. The diodes are there in case it fails, then it would still get battery voltage.

[Magician]

I like your thinking outside the box.
I've also thought about hooking up one of those new battery jumpstart devices that are small like the size of a iPhone 6+.. use it to helps start the car when not able to roll start it. They claim it will jump start a car like 20x per charge. They only cost around 50.00. You can carry it with you indoors to keep it warm in thee winter. Anyone have any thoughts on this approach?

[Stubby79]

Those are regular lipo batteries. They will have a normal voltage drop as they get more and more discharged, somewhat like a lead-acid. They have 3 cells in them, which when fully charged are 4.2 volts each = 12.6 volts. Fully discharged, they will be down at 9 volts. Your car wont run on 9 volts. It will probably stop running around 10 volts.

I have one of those jump packs. I haven't had to use it yet. We were just discussing them on another forum...the one guy who had tried using his, well, it wasn't strong enough to boost his car, even though the main battery wasn't completely dead. So I wouldn't count on it for doing much more than boosting a battery that can almost turn the car over already. I suppose you could throw in some super capacitors, but now you're getting more and more complicated.

They also have a small capacity. 8 amp-hours. Which isn't going to last long if you put a continuous load on it.

Oh and you can't make it exceed it's 12.6v limit, so no running an alternator with it hooked up. Or you'll have a fire on your hands.

They have their uses. They're a convenient size. If I ever use mine to jump start a car, I'll offer some more feedback.

[Magician]

My thought was instead to use a 50 or 100 watt flexible solar panel with controller... that is mounted on the roof and thus no noticeable drag along with a good sized marine battery. The only time this would pose any issue would be for long trips at night. I wouldn't use my lamps in the daytime and so would never have any real issues then. This would keep my battery pretty well topped off most of the time. I have all LED exterior lamps except the headlights, but will have those soon. I'll merely remove the alternator belt and keep it in the trunk if I ever get in a pinch.

[Stubby79]

I do most of my driving in the dark...I'd probably settle for having the alternator disconnected, except for when I'm braking. Or when the throttle position sensor reads zero.

Hmm...might have to try that.

[teoman]

There was a recentish thread about a circuit to change the output of the alternator on demand.

Make it work more like regenerative breaking, or make it compatible with other battery voltages.

[cRiPpLe_rOoStEr]

The so-called "intelligent alternator" setup currently fitted to newer cars is a good idea, since it reduces the drag to the engine when the electrical load is lower but still favors the engine-braking when it engages.

[Magician]

That's a great technology... I thought it would be great if they did that and you just answered that thought...

I just bought a 13 W suitcase style solar charger... forgot the controller...will be here by Friday. It's supposed to be great for solar charging devices like laptops cellphones etc and keep a car battery topped off and charge up etc... It's just over 1 Amp, so nothing major, but I want to see how it will perform for keeping my car charged up. I plan on taking the alt belt off and testing on my drives to and from work... only about 6 miles, so I am pretty sure this thing will easily keep with that usage. My MPGuino can keep me alerted to the battery voltage
If for some reason this has trouble keeping up, I'll just up to a 50W or 100W panel.

[Stubby79]

Originally Posted by Stubby79

I have one of those jump packs. I haven't had to use it yet. We were just discussing them on another forum...the one guy who had tried using his, well, it wasn't strong enough to boost his car, even though the main battery wasn't completely dead. So I wouldn't count on it for doing much more than boosting a battery that can almost turn the car over already. I suppose you could throw in some super capacitors, but now you're getting more and more complicated.

Regarding this...

I still haven't had to jump start a car with mine, but I came up with the idea to load-test the jumper pack with my(cheap) car battery load tester. It's supposed to be a 100a load at 12v. Hooked up to the jump pack, the voltage sagged down t 8.0v with the load on. which would mean the amperage would have dropped as well, down to ~66a.

That won't start a car by itself. As I said before, it might be enough in parallel with your half dead car battery to get it to turn over.

Hope that's some useful feedback on these little jump-packs.