RV.Net Open Roads Forum: Tech Issues: Solar and Charger into one?

RV Blog

  |  

RV Sales

  |  

Campgrounds

  |  

RV Parks

  |  

RV Club

  |  

RV Buyers Guide

  |  

Roadside Assistance

  |  

Extended Service Plan

  |  

RV Travel Assistance

  |  

RV Credit Card

  |  

RV Loans

Open Roads Forum Already a member? Login here.   If not, Register Today!  |  Help

Newest  |  Active  |  Popular  |  RVing FAQ Forum Rules  |  Forum Posting Help and Support  |  Contact  

Search:   Advanced Search

Search only in Tech Issues

Open Roads Forum  >  Tech Issues

 > Solar and Charger into one?

Reply to Topic  |  Subscribe  |  Print Topic  |  Post New Topic  | 
Page of 3  
Next
Sponsored By:
ajriding

st clair

Senior Member

Joined: 12/28/2004

View Profile



Posted: 01/23/20 06:56pm Link  |  Quote  |  Print  |  Notify Moderator

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?

BFL13

Victoria, BC

Senior Member

Joined: 02/15/2006

View Profile



Posted: 01/23/20 07:07pm Link  |  Quote  |  Print  |  Notify Moderator

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/pro........er-converter-battery-charger-w-led-light


1. 1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
See Profile for House electronics set-up.
2. 1991 Bighorn 9.5ft Truck Camper on 2003 Chev 2500HD 6.0 Gas

Lwiddis

Near Annett’s Mono Village, Bridgeport, CA

Senior Member

Joined: 08/12/2016

View Profile



Good Sam RV Club Member

Offline
Posted: 01/23/20 07:44pm Link  |  Quote  |  Print  |  Notify Moderator

“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?


Winnebago 2101DS TT & 2020 Chevy Silverado 1500 LTZ Z71, 300 watts solar-parallel & MPPT, Trojan T-125s. TALL pole for flags. Prefer USFS, COE, BLM, NPS, TVA, USF&WS, state & county camps. Bicyclist! 14 year Army vet - 11B40 then 11A - (MOS 1542 & 1560)


ajriding

st clair

Senior Member

Joined: 12/28/2004

View Profile



Posted: 01/23/20 08:11pm Link  |  Quote  |  Print  |  Notify Moderator

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…

DrewE

Vermont

Senior Member

Joined: 08/23/2014

View Profile


Offline
Posted: 01/23/20 09:01pm Link  |  Quote  |  Print  |  Notify Moderator

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.)





pianotuna

Regina, SK, Canada

Senior Member

Joined: 12/18/2004

View Profile


Offline
Posted: 01/23/20 09:32pm Link  |  Quote  |  Print  |  Notify Moderator

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.


Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp hours of AGM in two battery banks 12 volt batteries, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

mbopp

Henrietta, NY, USA

Senior Member

Joined: 06/20/2004

View Profile



Good Sam RV Club Member

Offline
Posted: 01/24/20 06:21am Link  |  Quote  |  Print  |  Notify Moderator

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.


2017 Grand Design Imagine 2650RK
2019 F250 XLT Supercab
Just DW & me......

ajriding

st clair

Senior Member

Joined: 12/28/2004

View Profile



Posted: 01/25/20 08:44am Link  |  Quote  |  Print  |  Notify Moderator

thanks.
Maybe i will just keep the old charger/breaker box in storage…It is heavy at 20-25 lbs anyway.

I realized too that the chest fridge will prefer AC power when available, duh, so there will not be a lot of demand on the battery when plugged in.
Maybe I can just have a trickle charger available.

I am doing a lot of unconventional things with this project, so while a fun challenge, is complicating it all.

I am thinking of mounting the two batteries on the outside in front of the jeep fenders (aerodynamically neutral) and also the generator behind the fender. Literally, thinking outside the (cargo) box..

pianotuna

Regina, SK, Canada

Senior Member

Joined: 12/18/2004

View Profile


Offline
Posted: 01/25/20 10:08am Link  |  Quote  |  Print  |  Notify Moderator

ajriding,

The acceptance rate of charge on a lead acid battery drops to about 12.5 amps per 100 amp-hours of capacity at 85% of full. As the battery becomes more and more charged that number drops a heck of a lot. Increasing the charge voltage simply causes the battery to gas. It is possible to fully charge at 12.8 volts--but it would take about 176 hours.

BFL13

Victoria, BC

Senior Member

Joined: 02/15/2006

View Profile



Posted: 01/25/20 10:17am Link  |  Quote  |  Print  |  Notify Moderator

Using a charger instead of a converter means using the batteries until they get low and then recharging, repeat.

A converter will stay on at 13.6v and run your 12v loads with no draw on the batteries, so that is what you want. It can also act like a charger when required to do so.

A "trickle charger" that stays on constant voltage at low amps would be ok for storage time battery maintenance, but while camping the low amps means it likely can't run the 12v things in the rig all by itself, so the batteries will still get low.

Therefore you want a converter with enough amps. AFAIK, this is the lowest priced one that can do the job you want as long as your total expected 12v draw at any time for a mix of 12v things is under 15 amps. $87 and free shipping:

https://www.boatandrvaccessories.com/products/powermax-pm4-15-converter

Reply to Topic  |  Subscribe  |  Print Topic  |  Post New Topic  | 
Page of 3  
Next

Open Roads Forum  >  Tech Issues

 > Solar and Charger into one?
Search:   Advanced Search

Search only in Tech Issues


New posts No new posts
Closed, new posts Closed, no new posts
Moved, new posts Moved, no new posts

Adjust text size:




© 2020 CWI, Inc. © 2020 Good Sam Enterprises, LLC. All Rights Reserved.