Solar charging vs converter vs tow vehicle - Fiberglass RV


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Old 01-12-2018, 02:34 PM   #1
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Solar charging vs converter vs tow vehicle

Being from an electronics background, the idea of 2 charging systems connected to the same battery bothers me... in particular solar + ac charge controller, or solar + tow vehicle alternator... I would expect these two power sources to fight as each has their own idea of a 3 stage charging algorithm...

the DC converter people don't make any mention of solar... and the RV solar controllers barely mention AC powered converters, or tow vehicle alternators.
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Old 01-12-2018, 03:16 PM   #2
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Yeah, I wondered about my solar panel and tow alternator both trying to push electrons into my battery at the same time. But after three years and 30,000 miles they seem to play together well. I don't even need to add water very often, about once per year. I suspect the solar charge controller will taper off its charge as the battery fills, probably the tow's alternator has a controller too and does the same. The battery never gets very low anyway. 12.4 is the usual low voltage unless we are parked for several cloudy days. Could be one sees the charging current coming from the other and just shuts off. Quien Sabe?

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Old 01-12-2018, 03:48 PM   #3
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Originally Posted by John in Santa Cruz View Post
Being from an electronics background, the idea of 2 charging systems connected to the same battery bothers me... in particular solar + ac charge controller, or solar + tow vehicle alternator... I would expect these two power sources to fight as each has their own idea of a 3 stage charging algorithm...

the DC converter people don't make any mention of solar... and the RV solar controllers barely mention AC powered converters, or tow vehicle alternators.
John, there are folks here that will tell you it's fine. I'm not one of them. Twenty five years teaching at the tech school I saw a lot of power supplies cooked . But then students will be students . Besides we had a tech to put the pieces back together. I suspect most connections will not destroy anything but unwanted oscillation might be an issue. If you wish to tie everything together you could make an OR gate with diodes to isolate the sources. Bad for the output impedance but solves the isolation issue. My solar is attached with gator clips. My charge line has a factory relay. That's my solution. Lots of folks have permanently wired solar. I don't recall problems reported when they plug in to shore power but if it was singing like a bird they might not notice. Hope that helps. Raz
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Old 01-12-2018, 04:14 PM   #4
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If you wish to tie everything together you could make an OR gate with diodes to isolate the sources. Bad for the output impedance but solves the isolation issue.
It takes 0.7 VDC to forward bias a diode. That would mean that if the solar controller was outputting 14.4 VDC, to charge the battery, then the battery would only see 13.7 VDC. I am no battery expert, but I have to think that at the very least, the battery is going to charge much more slowly. Possibly not completely either.
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Old 01-12-2018, 04:24 PM   #5
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It takes 0.7 VDC to forward bias a diode. That would mean that if the solar controller was outputting 14.4 VDC, to charge the battery, then the battery would only see 13.7 VDC. I am no battery expert, but I have to think that at the very least, the battery is going to charge much more slowly. Possibly not completely either.
You could use germanium diodes. Or better yet, schottky diodes. In all seriousness, I don't think it's a big issue.
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Old 01-12-2018, 04:33 PM   #6
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Virtually every motorized RV today puts out 14.5 volts to charge the chassis and house banks. If the engine is running the alternator is managing the output.
Almost every solar controller cuts off at about 14.5 volts also. Some of the better ones are adjustable but the vast majority of non adjustable controllers cut out at 14.5 volts.
Charge converters can indeed charge as three stage bulk, absorb and float. But most cut out around 13.6 however some can go higher.
The magic number for a battery bank, charge converter, solar controller and battery bank such as two, six volt GC2’s in a bank is 13.6.
Almost every OEM I know of, wires their coaches to charge the battery bank off all three charge sources at the same time.
I have seen some folks recently who connect their solar panel to their battery bank without a regulator. That arrangement can lead to overcharging for sure.
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Old 01-12-2018, 09:32 PM   #7
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both the PWM solar controller (a 2014 vintage GoPower 30A PWM) and the WFCO dc converter in my escape are 4-stage chargers, they put out around 14.4V to bulk charge, then 13.8V or whatever for the absorption phase, then 13.2V for maintenance.

the alternator in my Tacoma seems to have a 3 stage regulator too, as I've seen 14.4V a few minutes after starting it, then after its been running awhile, 13.8V
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Old 01-13-2018, 12:27 AM   #8
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both the PWM solar controller (a 2014 vintage GoPower 30A PWM) and the WFCO dc converter in my escape are 4-stage chargers, they put out around 14.4V to bulk charge, then 13.8V or whatever for the absorption phase, then 13.2V for maintenance.

the alternator in my Tacoma seems to have a 3 stage regulator too, as I've seen 14.4V a few minutes after starting it, then after its been running awhile, 13.8V
Your GoPower solar charge controller is a 4 stage charger, but I can assure you the charger in the WFCO 8955 is not. The WFCO doesn't have an equalization/desulfation cycle.
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Old 01-13-2018, 08:02 AM   #9
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I pull WFCO products out of units every day and put in the trash. Hundreds.
I use Progressive Dynamics converter chargers and if you get the 9200 series they are a true three stage unit. As long as they have the charge wizard installed. Very good products.
Solar is changing a lot these days. From PWM to MPPT is a big change.

It would be interesting to know if a vehicles alternator was three stage. I’ve always believed that an alternator will put out as much as the battery or load can take. The lower a battery’s state of charge will allow a higher charge from the alternator from what I have always known.
Time to do more research!
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Old 01-13-2018, 11:46 AM   #10
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ah, the wfco 8955 is a 3-stage, not 4-stage.

and yeah, older cars, the regulators on the alternators just limit the voltage to 13.8 or so and dump as much current in as they can. the one on my 2008 tacoma seems to be a little fancier than that, but I'd need to drive around with a voltage monitor to actually confirm that.
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Old 01-13-2018, 12:18 PM   #11
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I have had no problems with multiple charging sources - that includes on roof solar panels with a built in controller, a portable panel with its own controller, a vehicle charge wire, and a converter. Not all run at once (tow vehicle & converter would be interesting), but any time I'm in a campground with electrical hookups, the converter & solar are both active, and when driving, the tow vehicle charge line & roof top solar panels are active.

The only time I notices an interaction problem with the two solar systems was when the portable panel was in full sun & the rooftop panels were in partial sun. The roof panels & controller produced enough voltage that the inexpensive portable panel controller would not provide full output. This only happened once or twice in months of dry camping...

Before adding the capability of feeding the portable panel directly into the trailer controller, when dry camping, I sometimes ran both the roof panel & a portable, the only problem mentioned above.

Currently, I have a pair of 160 watt panels on the roof feeding a 4 stage GoPower controller, and a 160 watt portable panel that has the controller bypassed & is fed into the input of the GoPower controller.
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Old 01-14-2018, 10:26 AM   #12
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agree with the OP....

I too was not sure if having the different charging systems connected together would have any adverse effects.....BUT I was sure that it was going to limit my ability to assess the effectiveness of each one separately. How would you tell???

I did not have 12V power coming from the TV from the start...so that was easy....and I still don't.

I don't have a converter anymore...12V power is fed from the batteries all the time. My charger is on it's own dedicated breaker so I can turn it on or off at will.

I have two rooftop panels (70W total) and one "deployable" (40W)....all three are wired to a single charge controller. I have an on/off switch between the panels and the controller.

My whole system is "MANUAL"....I can plug into shore power, have AC in the coach and NOT be charging the batteries...if I choose. If I leave the charger breaker on (which I do in most instances) when I plug in the charger starts up and does it's thing...if I am parked in full sun at the time I turn the panels off....or I could do the reverse if I wanted to (charger off, panels on)

it works for me... I like to think I get a lot of useful information this way....I'm a "happy camper"
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Old 01-14-2018, 12:14 PM   #13
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I too was not sure if having the different charging systems connected together would have any adverse effects.....BUT I was sure that it was going to limit my ability to assess the effectiveness of each one separately. ...)
Good point. My situation is similar.
  • On the road, the tug charges.
  • On shore power converter charges, but it's on a breaker so can be shut off at anytime, such as in the case of....
  • Off shore power or when I feel like getting free power, its a portable solar panel (which is also on a breaker and can be disconnected from inside the camper).
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Old 01-14-2018, 10:28 PM   #14
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I just put switches between panels & charge controller, and between charge controller & battery. When plugged into either tug or shore power, I switch off the solar panels.
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