Blue Seas Automatic Battery Relay and MPPT

Re: Blue Seas Automatic Battery Relay and MPPT

bstory wrote: »

I am new to this forum. I have done some searches but can't find specific info on using an MPPT solar controller such as the Morningstar 15 amp one in a 12 volt camper where I already use a Blue Seas 120 amp dual sensing smart battery combiner/isolator to charge my 2 AGM house batteries from the vehicle's alternator.

Generally, a vehicle alternator is not a very good way to charge deep cycle batteries... Typically an alternator is setup to charge at 13.8 to 14.2 volts. It does not charge the battery bank very quickly (or provide equalization charging voltage when needed). And many RV setups have long cables between the alternator and the house battery bank which adds even more voltage drop (usually a trailer setup).

This is the only charging system for the house batteries at present but I am getting a 130 watt Kyocera panel and had planned to use it with an MPPT controller. My question is how to wire it in relation to the Blue Seas combiner/relay to avoid having conflicts - 2 charging sources into the house batteries at the same time, damage to the MPPT controller, undoing the effectiveness of the MPPT controller.

You can setup charge controllers in parallel and they will work OK. The charge controller with the highest voltage set point will be the "winner".

The only possible problem that I see--If you have the solar charge controller set to equalize your battery bank and you have your vehicle running (battery isolator "on")... It could bring your vehicle 12 vdc system to 15.0-15.5 volts and over charge the vehicle battery and possibly damage your vehicle electronics... However, with a single 130 watt panel, I don't think that will be an issue (vehicle electronics will probably draw enough current to keep the battery voltage down). In any case, you should not equalize when the vehicle is running/battery isolator turned "on" as you do not want to equalize your vehicle battery.

My second question, maybe answered in conjunction with the first, but maybe also a separate questions, is how to use these components to also top off the vehicle's starting battery when it needs it from the Kyocera panel?

If you can manually turn your isolator "on" (or manual switch)--just charging all of the batteries in parallel will work. Be careful though, deep cycle batteries are charged at 14.5+ volts and can "boil" the vehicle battery and even though it is probably a maintenance free battery--you will need to check the electrolyte levels and add distilled water.

You can also get a Morningstar Dual Battery Charge Controller 25 Amp for this application. It is a PWM controller, but would work fine here.

Anyone with experience with a Blue Seas automatic combiner/isolator and an MPPT controller?

By the way, for a single solar panel (or a pair on short cables directly mounted to the RV), I am not sure an MPPT controller is really cost effective for you.

Yes, in sub freezing weather and panel pointed towards sun, you can get a 10-15% or so increase in output power--But that is about it.

Where MPPT controllers are very nice is if you have a long cable run between the charge controller and the solar array... Such as a 50' cable where you put the panels in sun (mounted securely so the wind does not blow them over and break the glass) and the RV (parked in shade).

In those cases, you place the panels in series so that Vmp=35+ volts... This reduces the current and increases allowable voltage drop--allowing you to use much lighter cable for the run (like a 10 AWG extension cord instead of 4 awg cable).

Also, if your setup is in very a very hot region (desert), Vmp falls with increasing temperature. You can put two panels in series to get the full 15+ volts available for charging/equalizing your battery bank. A PWM panel with Vmp=17.5 volt panel in hot weather may not be able to fully equalize the battery bank (just during the few hot days of summer--usually not a major issue).

Here is a thread where Kevin installed a couple solar panels and a Morningstar MPPT 15 amp charge controller+battery monitor in his small RV trailer.

-Bill

Re: Blue Seas Automatic Battery Relay and MPPT

bstory wrote: »

Just to clarify my situation, since I have Lifeline AGMs I don't forsee having an equalization cycle set up. The alternator doesn't do that automatically does it? So if my assumption is correct then I don't need to worry about the equalization danger?

Yep, now worry about equalization (in general).

Second, the house batteries and blue seas automatic combiner/isolator are installed right under and behind the driver's seat and the starting battery is right in front of the driver so I think they are only about 4- 5 feet apart - no long runs.

Still a good idea to measure the battery voltages with a good DMM and see what they are reading. Extra 5 feet of wire, battery isolator, etc. can do some surprising things. Batteries have very little internal resistance (on the order of 0.010 to 0.001 Ohms) and a very precise chemical/voltage relationship. Anything that assumes different will usually result in much lower charging currents than you would expect.

Third, I didn't mention earlier, but I may want to add a second 130 watt panel later or even a higher voltage panel at some point - that's why I was leaning toward the MPPT controller, but the issue you raise about cost-effectiveness is worth thinking through. Do all the concerns about two charging sources disappear in your mind if the solar controller is not an MPPT?

MPPT and PWM both can run in parallel with other charging sources (assuming proper wiring practices).

The big advantage of MPPT over PWM is long wire runs from the solar array to the charge controller. MPPT allows you to put 2 or more (sometimes) panels in series which dramatically reduces the copper wire requirements (1/2 or 1/4 the cost of wiring).

The newer controller designs are usually MPPT -- So if you want computer logging, panel meters, etc., MPPT may offer you more options (at a higher price).

-Bill