Solar alternator assist?

[California98Civic]

The ecomodder wiki has an item on solar assistance for the alternator, but it seems to assume an outside mounting and that you are trying to replace the alternator. My Civic has a rather large dash and panels are smaller by the day. Anyone have an opinion on the possible effectiveness of a smaller panel, on the dash, used to back-up the alternator so that it does not switch on very often? I located, for example, a cheap, lightweight, and smallish panel online but I have seen some ecomodders suggesting 10% gains from an alternator delete... Since any gains from this idea would be a lot less... not worth it?

[Joenavy85]

it would be extremely costly. if you figure even just a 2 Amp draw, you're talking about 24+ Watts, a 20 Watt panel is pretty big, most dash mount battery maintainers are less than 2 Watts

[Frank Lee]

I'd think to get any benefit you'd have to control your alternator such that when you park the battery is somewhat discharged... so that the cells have something to do. But you don't want it too discharged in order for it to start right up again. Then maybe a two-battery system makes sense.

[Joenavy85]

you can find battery wiring set ups that are for dual battery sets that will isolate one of the batteries to use when restarting the engine

[Joenavy85]

JayCorp DBKIT Dual Battery Kit with Voltage Sensitive Relay VSR

[California98Civic]

Thanks all. I had a feeling there were a few things about electricity I did not yet fully "get." My dash is big, but it's not that big!

[Ryland]

The extra layer of glass is going to cut down on the output, I'm not sure where the 2 watt figure came from because the solar panels that come with VW's as they are shipped from Germany are 5-10 watts depending on the version you can find.
If you want to get the greatest affect then I think charging a 24v battery pack then stepping that down to 13.8v so the alternator sees the battery as fully charged and shuts down.

[Joenavy85]

the 2 watt figure came from the average plug in battery maintaining solar panel you can get on ebay or amazon. i like the 24v stepped down to 12v idea, would probably work pretty well, might take a little more to recharge them, but if it's not a daily driver it could work

[fjasper]

Might it work to use a 13.2v or 14.4v battery? The alternator would feed it at ~14v, which would keep it mostly charged, but it would have the ability to absorb additional power from a higher-voltage source when available.

I think cells are 1.2v, so by using 11 or 12 cells, you could make a battery that's a slightly higher voltage. I don't know enough about it to predict how it would behave, though. The charging system voltage might not be enough to maintain a useful charge in a 13.2v battery.

I'm thinking NiCd or NiMH, but only because I don't know of a source for 1.2v lead-acid cells.

Like maybe 11 of these in series for 13.2 nominal voltage, 10 Amp-hour capacity? I guess that gets a little bit expensive, and would require some additional electronics to control charging. NiCd are supposed to be able to supply very high discharge rates (up to 50 times capacity), so CA should be significantly higher than a lead-acid battery of the same amp-hour capacity (as much as 20 times higher). Read more on Wikipedia.

The PC680 is my benchmark, since it has good power for applications that take relatively high starting current for small engines (BMW boxer twins). It's also certified (in slightly different form) for cranking 300+ cubic inch airplane engines, and it shows 17 amp-hours' capacity.