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Inverter/charger with Solar question


sushidog

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I have a question about how an inverter/charger works in conjunction with a solar system in a trailer.

 

If my solar system is working, charging my batteries (let's just say through a Tristar TS-60, or other quality MPPT charger, if the answer is equipment dependent ) and I decide to plug my inverter/charger into the CG pedestal or fire up my generator will the inverter charger's output be additive (assuming my batteries are low), will it override the charge coming in through the solar panels or will it not function until I disconnect the solar controller?

 

Let's look at an example to make my scenario clear. It is an overcast day so my solar panels ( I'm planning on building a large, high voltage system) are only delivering say 5 amps to my batteries. I have been boondocking for a while and am just overnighting in a FHU RV park to dump my tanks, watch some cable TV and charge my batteries. When I plug into the pedestal I wonder if my planned 15 amp (48v) inverter charger will add to the 5 amps of solar and charge my batteries at a 20 amp rate? If not, what amperage will my batteries be charged at (assuming they are low will accept a high charge rate)? Or what can I do to allow both chargers to work in unison if they don't like to work this way? What if I purchase a stand alone 15 amp 48v battery charger if an inverter/charger wont perform as intended? Can this be used in conjunction with a solar charger or will it confuse/damage the electronics of either charger?

 

Just to explain my plans, I will be keeping my 12v converter to power my 12v needs while hooked-up and charge my stand alone 12v battery (probably two, GC-2s) for smaller power draws such as: slides, lights, fridge board, etc. I will also use a separate solar charge controller to keep the 12v side working (unless anyone knows of a single charge controller that can charge both 12 and 48v battery banks simultaneously. My 48v battery bank will be reserved exclusively for a 48v DC heat pump and inverter use. It would be simpler to get rid of the 12v side altogether, but no one that I know of makes 48V RV fridge boards, lights, slide motors, etc. My other alternative is just to switch everything (except my heat pump) over to AC power and get a bigger or a second inverter, which would greatly simplify things. What would you guys do? An all ac powered trailer or one with 12v, 48v and 120v ac power?

 

Chip

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I have a question about how an inverter/charger works in conjunction with a solar system in a trailer.

 

If my solar system is working, charging my batteries (let's just say through a Tristar TS-60, or other quality MPPT charger, if the answer is equipment dependent ) and I decide to plug my inverter/charger into the CG pedestal or fire up my generator will the inverter charger's output be additive (assuming my batteries are low), will it override the charge coming in through the solar panels or will it not function until I disconnect the solar controller?

 

There are a lot of variables there. It is fairly equipment dependent. In "most" cases (with higher end inverter/charger and in-line sensors) they will "handshake". Or as you said.. be "additive". It will not override the charge and it is not necessary to disconnect your solar controller. Each unit will simply apply power as needed within their respective charge algorithms. In the case of the Tristar.. I have found it to be more responsive than my Magnum inverter/charger... allowing the Mag to supply the bulk of the charge and the Tristar just 'helping out' when needed, or when an additional load is added during the charge cycle, it will up the juice from my panels to meet the load. The Mag will as well, but responds a little slower so the Tristar generally picks up the load before the Mag has a chance to respond.

 

Does that make sense? The main trick there is having a fully programmable charger to ensure the battery charger and the solar controller are "on the same page".

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Multiple charging sources can get really tangled, particularly ones based on voltage alone. A good charger will monitor both voltage and battery current and adjust as needed to keep the proper levels of each to insure a complete and safe battery charge. As soon as you add a second charger all that goes in the bin since the original charger has no way to figure out battery voltage since it is now overridden by the voltage from the other charger and it can't likely make much sense out of the battery current readings as it will be seeing current from the other charger that it can't control.

 

There are situations where this isn't really important, bulk charging of a large bank where the bank can safely accept the total charge current from all connected charger is one. In that situation the multiple chargers will add and not hurt anything.

 

That situation doesn't last long and as the bulk stage ends and you move to acceptance you are back to needing a single charger with voltage and current sensing to get the best charge.

 

Trying to charge two differently loaded and sized battery banks at different voltages really calls for two completely separate charging systems. Trying to do anything else is going to get complicated but you could try supplying all your charging at 48 volts and then stepping down to 12 using a charger similar to a MPPT solar controller to accomplish the task.

 

Another option is to draw your 12 volts off the 54 volt bank, either stepping down or using a bank splitter - equalizer to get the right voltage and keep the battery charge even.

 

I looked at having both voltages in my last fiver and it just didn't make sense for me, for you the extra expense may be worth it to run your cooler but it is going to add a good bit to the cost, complexity and aggravation of the system. Don't even think about what it will do to your resale value when you try to explain it to a potential buyer that isn't an electrical guru.

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I hit the breakers to the solar panels if we have the engine running. If we have shore power I either use the solar panels exclusively (and keep the breaker tripped to the charger/converter) or turn the solar panels off.

 

I generally favor the expensive solar charge controller over any of the others because it is more granular in its configuration. And, besides, I like the idea of having most of our power come from the sun. Our draw off the 12v system when we're parked isn't much anyway; if we have shore power then we also have microwave and air conditioners. If we are off the grid then I can always run the generator for microwave and air conditioners. The generator needs to be run now and then anyway.

 

Theoretically you can design the charging systems to each work with each other with one taking priority by having setpoints different than the others. In practice it's a PITA and more work than even *I* am interested in (and I fiddle with this stuff a lot).

 

WDR

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Thanks folks, for the great replies. I sort of thought there wouldn't be a major problem integrating the two, say with the inverter/charger damaging the solar charger or vica versa, but just wasn't sure. You've put my mind at ease as far as one component destroying another. I'm still not sure how such a system will work in practice - I guess "it depends" sums things up and my best bet will be to try to duplicate someone's exact equipment - which might be a challenge, as not many folks have gone to 48v systems yet. On the upside, components for 48v systems are rare and hard to find, so I might be able to turn the limited selection of 48v inverter/chargers to my advantage.

 

Stanley, I looked at a bank splitter (equalizer) seriously considering this option, but in addition to them being expensive (a quality 48/12v 30amp splitter costs over $450 http://www.altestore.com/store/Charge-Controllers/Battery-to-Battery-DC-Chargers/Solar-Converters-EQ-1248-30A-DC-to-DC-UpDown-Converter/p1291/ ) and still probably won't power a slide (especially with other phantom loads.) A stand alone 12v battery, even if a simple Group 31 or a couple golf cart types would be considerably cheaper not to mention adding additional battery capacity too, rather than drawing from an already heavily tasked 48v bank. I'm leaning more and more to the simple a/c only approach, (ditching all 12v DC components) which would allow me to go with an efficient, larger house fridge rather than an typical RV absorption unit. I guess my best bet is to look as some smaller "park model" style TTs that already are set-up primarily for 120v a/c.

 

As far as resale, I plan on my next RV to be my last RV, making resale irrelevant. If this proves not to be the case then I will move my solar system to my new trailer as no one would pay me a fraction of what a max solar system would be worth to me, not to mention what I ill eventually end up spending to build a solar boondocking system of my dreams.

 

Chip

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