I am modifying my cargo trailer to be more like a camper, and dug up some old stuff for it.I have a modern MPPT solar controller for the 100 watt (soon to be 200w).Two golf cart batteries.I have an old 12.7 volt, 15 amp DC power source of a 1972 Winnabago, attached to a 115 circuit breaker box complete with shoreline/generator switch.I am sure there is no monitor on the DC charger/power source.The solar I know how to set up no problem, no questions.The power source no problems either.What I want to do is have the shoreline DC power source be "smart". I do not want to just send 15 amps to the battery everytime I plug in or want to use the DC power source instead of the batteries. I will be running a Danfoss chest fridge, and just minimal lights and minimal charging, min fan etc.I do not want to buy a $500 controller that controls both power sources (solar and charger) electronically, but can spend under $50 for something to make it all work together.The breaker box does have a breaker for the charger if it comes to that so I can still plug in and have shore power for AC or electric heat without charging (overcharging) the battery.I would rather have something monitor the battery automatically, so looking for a thing maybe to go between charger and the battery to control the charge while the solar works in the daytime but not at night.Keeping the battery in float while running the fridge and outlets off the charger/converter is the most preferred solution. Anyone tackled this?

12.7 volts is not enough to charge a 12v battery. That power source would just be able to run some 12v things such as lights and fans.It is useless for what you want to do.BTW it does not "send 15 amps". What it does is provide that 12.7 volts. Whatever amps you get depends on how much lower the "load" is in voltage. Where the battery is the load at say 12.4 volts, the 0.3 volt difference will not make for many amps at all.You just have to triple that $50 budget and get a proper converter. EG:https://www.boatandrvaccessories.com/products/powermax-pm3-60lk-12-volts-60-amp-power-converter-battery-charger-w-led-light

“I do not want to buy a $500 controller that controls both power sources (solar and charger) electronically, but can spend under $50 for something to make it all work together”Good MPPT solar controllers are way under $500. Try $199. https://www.windynation.com/Charge-Controllers/Windy-Nation/WindyNation-TrakMax-MPPT-40A-Solar-Charge-Controller-12-or-24-Volts-for-Sealed-AGM-Gel-and-Lithium-Batteries-with-Opt/-/3403?p=YzE9MTc=Did you mean a controller that handles solar and 110?

hmm, Im not sure I follow your logic on amps.You are right, if it is only 12.7 volts then that will not matter if the solar is charging at 14.This is 1970's technology, 15 amps is a decent amount of power to flow continuously. I don't think the 15 amps are variable, I think it just puts out 12.7 at 15amps, so the battery state will not alter what the charger does, it just does it no matter what. How the battery takes the power is different.Am I missing something?I will have to take actual measurements when I can plug it in and connect to a battery. I cut this out of my wrecked Rv a few years ago, but remember when I switched to the charger (not battery) that the lights got much brighter, so that suggest more like 14 volts than just 12.7 as batter would be12.4-12.6 at the same time…The solar and MPPT are all that is needed to take care of the power, but on rainy days, or heavy shade, or cloudy short winter days I would like the option to supplement…

It is not possible to construct a charger that simultaneously provides a fixed constant voltage and a fixed constant current. The two are intimately related; at a given state of charge (and temperature and so forth), there is a single voltage vs current curve that applies to the battery. It is closely related to Ohm's law, although the relation between voltage and current is not precisely linear in this case.Your charger might put out 13.something volts under a small load (low current required) which tapers down to 12.7 at 15A. There are plenty of other things that could be going on, too, such as seeing the effects of an old split output converter.At any rate, I think you would be well served to replace the charger with a modern multi-stage unit, such as a Progressive Dynamics PD9245. It is more than $50, but worth the money and kinder to your batteries. (I guess if you rely on solar nearly exclusively it makes little matter what converter or charger you have.)

Hi,I'd want to "see" the output on that old power supply. I'll bet you dollars to donuts it has lots of "ripple". I would certain NOT use it.

Solar and Charger into one? | Good Sam Community

mbopp
Explorer
Jan 24, 2020
Typical float voltage is 13.2 to 13.6V. If you can set your power supply to that range it'll help.
The old Elixir converters were single stage, fixed output.
And the old Magnetecs were a dirty converter that had to be connected to a battery to smooth out the ripple.
pianotuna
Nomad III
Jan 24, 2020
Hi,

I'd want to "see" the output on that old power supply. I'll bet you dollars to donuts it has lots of "ripple". I would certain NOT use it.
DrewE
Explorer II
Jan 24, 2020
It is not possible to construct a charger that simultaneously provides a fixed constant voltage and a fixed constant current. The two are intimately related; at a given state of charge (and temperature and so forth), there is a single voltage vs current curve that applies to the battery. It is closely related to Ohm's law, although the relation between voltage and current is not precisely linear in this case.

Your charger might put out 13.something volts under a small load (low current required) which tapers down to 12.7 at 15A. There are plenty of other things that could be going on, too, such as seeing the effects of an old split output converter.

At any rate, I think you would be well served to replace the charger with a modern multi-stage unit, such as a Progressive Dynamics PD9245. It is more than $50, but worth the money and kinder to your batteries. (I guess if you rely on solar nearly exclusively it makes little matter what converter or charger you have.)
ajriding
Explorer II
Jan 24, 2020
hmm, Im not sure I follow your logic on amps.
You are right, if it is only 12.7 volts then that will not matter if the solar is charging at 14.
This is 1970's technology, 15 amps is a decent amount of power to flow continuously. I don't think the 15 amps are variable, I think it just puts out 12.7 at 15amps, so the battery state will not alter what the charger does, it just does it no matter what. How the battery takes the power is different.
Am I missing something?

I will have to take actual measurements when I can plug it in and connect to a battery. I cut this out of my wrecked Rv a few years ago, but remember when I switched to the charger (not battery) that the lights got much brighter, so that suggest more like 14 volts than just 12.7 as batter would be12.4-12.6 at the same time…

The solar and MPPT are all that is needed to take care of the power, but on rainy days, or heavy shade, or cloudy short winter days I would like the option to supplement…
Lwiddis
Explorer II
Jan 24, 2020
“I do not want to buy a $500 controller that controls both power sources (solar and charger) electronically, but can spend under $50 for something to make it all work together”

Good MPPT solar controllers are way under $500. Try $199. https://www.windynation.com/Charge-Controllers/Windy-Nation/WindyNation-TrakMax-MPPT-40A-Solar-Charge-Controller-12-or-24-Volts-for-Sealed-AGM-Gel-and-Lithium-Batteries-with-Opt/-/3403?p=YzE9MTc=

Did you mean a controller that handles solar and 110?
BFL13
Explorer II
Jan 24, 2020
12.7 volts is not enough to charge a 12v battery. That power source would just be able to run some 12v things such as lights and fans.

It is useless for what you want to do.

BTW it does not "send 15 amps". What it does is provide that 12.7 volts. Whatever amps you get depends on how much lower the "load" is in voltage. Where the battery is the load at say 12.4 volts, the 0.3 volt difference will not make for many amps at all.

You just have to triple that $50 budget and get a proper converter. EG:
https://www.boatandrvaccessories.com/products/powermax-pm3-60lk-12-volts-60-amp-power-converter-battery-charger-w-led-light

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