solar battery tender

[blw2]

thanks Kevin!  I did a quick search.  the kits I'm seeing have what look to be surface mounted charge controllers.  I'm not sure where I could install it near the battery.  My understanding is that these need to be close to the battery.  Is that true?  the only place I can think would be inside the kitchen cabinet just after the wire leaves the fridge chimney...it would be closer to the panel than to the battery

 

[Kevin Means]

When installing a large inverter, it's important to use heavy gauge wire, and to install it close to the battery bank, because large inverters can draw a lot of current (depending on what appliance is being used.) It's not as big a deal when installing a smaller PWM controller, because we're more interested in reducing voltage loss on the wire run. You said you only have about a 15 foot run, so 12 to 16 gauge wire should work fine.

If given a choice of locations of where to mount the controller, I would install it as close to the battery bank as is practical. The controller will be reducing the voltage from your panel, so your batteries don't get over-charged, so there will often be less voltage between the controller and the batteries, than between the solar panel and the controller. We don't want that voltage being reduced any further by using thin gauge wire with a long wire run. Does that make sense?

Kev

 

[KandT]

When installing a large inverter, it's important to use heavy gauge wire, and to install it close to the battery bank, because large inverters can draw a lot of current (depending on what appliance is being used.) It's not as big a deal when installing a smaller PWM controller, because we're more interested in reducing voltage loss on the wire run. You said you only have about a 15 foot run, so 12 to 16 gauge wire should work fine.

If given a choice of locations of where to mount the controller, I would install it as close to the battery bank as is practical. The controller will be reducing the voltage from your panel, so your batteries don't get over-charged, so there will often be less voltage between the controller and the batteries, than between the solar panel and the controller. We don't want that voltage being reduced any further by using thin gauge wire with a long wire run. Does that make sense?

Kev

So does the controller reduce the volts down to about 13.8 or so??  Does it up the amps a hair to do this??

 

[Kevin Means]

So does the controller reduce the volts down to about 13.8 or so??  Does it up the amps a hair to do this??

In the bulk charging phase, PWM controllers are charging at about 14.4 volts with full, constant current. In the absorbtion phase (about 80% SOC) the voltage is still around 14.4 volts, but the current is reduced to prevent over-charging. In the float phase, voltage is reduced to about 13.8 volts, and the current is reduced to trickle charge the battery. (Keeping it topped off)

A PWM controller does not convert extra voltage to amps, however an MPPT controller does (but they cost more.) Some MPPT controllers are programmable for different types of batteries, to optimize charging. Generally speaking, RVers usually don't need a more expensive MPPT controller if all they've got is a typical 12 volt 100 watt panel, like the kind Brad is considering. The panel just doesn't generate enough extra voltage to justify the cost of an MPPT controller. Of course, that's just my opinion.

Kev

 

[blw2]

perfect.  very helpful, thank you Kevin!

and all the side questions/answers are helpful too! 

thanks