*Bump* with a bit of a side bar
I think I figured out what I need for solar but for the price I'm not ready to make that purchase just yet and with just a couple weeks until I plan on hitting the road I'm looking at setting up my battery bank and just using an isolator to charge them off my alternator. I figure it should be enough to run the roof fan and house lights for a weekend, everything else like fridge, TV, device charging can come later. So before I buy an isolator...
- Looking at
this isolator that I basically found by searching "battery isolator" on Amazon.
Someone around here years ago said they work at a cop shop and they use Stingers in their cop cars. All it is is a relay. You rig it as a "split-charge relay":
http://www.expeditionportal.com/for...ke-a-cheap-isolated-dual-battery-setup-for-50
Personally, if I was starting from scratch, I'd go with a relay capable of handling the full output of the alternator, and use wire big enough to handle that. But yea, the Stinger will work. My truck has a 100a alternator and an 80a relay like in the link above and it's worked without a hitch for years.
- I should need up to 60Ah/day (very generous estimate). Double that for the whole 50% charge rule, and for easy round numbers, I'd need at least 100Ah of capacity assuming I drive every day.
- I don't know much about alternators - how fast would this isolator charge my battery bank? If I'm consuming 50-60Ah/day how long would I have to run the engine to charge the aux back up?
If you have a new type computer controlled charging system, then it won't be too bad. If not, then you can expect to drive for a few hours to get the battery to 80% or possibly 90% (depends on the voltage that your voltage regulator is set to) and another 12-24 hours of drive time to finally reach 100% charged. If you're just idling...figure...oh...a week to get back to 100%. (Just kidding...it won't be a week...probably only be a couple of days.)
- Am I sacrificing anything by going this route?
Sacrificing multi-stage (bulk/absorb) charging.
Could I risk the alternator being unable to keep up with keeping my starter battery in prime shape? The whole reason for solar was because I don't ever want to risk a dead starter battery.
Starting the truck probably uses around 1/5 of one amp*hour. You could keep up with that using an alternator from a model airplane.
- Should I buy a battery monitor or something for a setup like this?
For a simple split-charge relay? Nah. I just use a voltage meter. After a while, you get a feel for how things are going.
Or is there some lucky difference where alternators regulate themselves?
If alternators regulated themselves, they wouldn't need voltage regulators. The voltage regulator just turns the alternator on/off to keep the voltage where it's supposed to be. (Unless you have a modern computer controlled charging system, then it's got some additional bells and whistles.)
- Installing these is as simple as connecting the starter battery to the battery bank in parallel, but putting the isolator inline with one of the parallel connectors? Does it matter if its the pos or neg?
Theoretically it doesn't matter. In the real world, if you put it in the neg then Santa moves your name to the naughty list and you have to start speaking Queen's English.
But seriously...if you put it in the neg, then how in the hell are your aux loads gonna work when your aux battery has the neg cable disconnected? You ground the battery permanently and use the relay to tie the aux battery to the charging system when the engine is running, and disconnect it when the engine isn't running.
- Any reason not to go with dual 6V battery bank in series, and connecting that in parallel to the starter as mentioned above? If no I can just get the solar batteries I'm planning for, if yes I'll just find something cheap that has the Ah I need for the time being.
No reason. 12 volts is 12 volts.
- Going this route, will I need to ground the battery bank to the frame/starter battery, or is the isolator good enough to keep things completely independent from the vehicle?
The "isolator" doesn't "isolate" the second battery from the vehicle. It only "isolates" the two batteries whenever the engine is off, so that your loads on the aux battery don't draw down the engine battery. So yes, you have to ground the aux battery to the truck somehow. Frame works, but for a really long run (20' or more) I'd run a dedicated ground alongside the hot back to the engine battery.