Adventures in Battery Charging

[ppine]

I recently fired up my solar controller for the first time in preparation for the first trip with solar panels. With shore power from the house, the best I can get out of the batteries is 12.3 volts after 24 hours on the converter.

I disconnected the shore power and plugged in a quality battery charger and the batteries miraculoulslly went to 12.7 volts in 10 minutes.

Can anyone explain what is going on here?

[CHICKDOE]

don't know what the comment about solar means.

on shore power the converter should be supplying about 13.6 volts to the batteries. take a reading at the battery terminal when you are not connected to shore power. (have solar off). a fully charged battery should be 12.6 volts or so. now plug into shore power and take the same reading. if converter is supplying power it should be around 13.6. if it is not find out why converter is not supplying power.

as far as the reading from the battery charger i don't know if the 12.7 is while the charger was connected or not. if it was taken immediately after the charger was disconnected it might be misleading as the batteries need to stabilize for many hours until the voltage reading is reflective of their status. take a reading the day after the charger was disconnected. you're not going to fully charge a battery in 10 minutes.

[ppine]

The rig sat over night on shore power, now the solar controller reads 12.1 volts on the two batteries. They are from 2017 but might be shot from being abused. This is getting confusing.

[rk06382]

Originally Posted by ppine

The rig sat over night on shore power, now the solar controller reads 12.1 volts on the two batteries. They are from 2017 but might be shot from being abused. This is getting confusing.

What are the details on your Solar panels & charge controller?

[CHICKDOE]

i'm certainly no expert but i hate trying to figure out things when there are mutliple variables going on. in this case shore power and converter, external battery charger, and solar.

i'd try to get a baseline. disconnect all but one power source. you say you have a quality battery charger. use it and only it to charge up the batteries for a day or so. then take your battery voltage measurements. or better yet take them in to an auto parts store to have them load tested. replace if not able to keep a charge. once you know that you have good batteries i'd then connect them to the converter and verify that it is working ok. once you know it is, then i'd connect the solar and again confirm that it is working.

[ppine]

Solar controller is a 40 amp MPPT. No solar panels are connected to it. I am just using it to monitor the battery charge. With a battery charger the controller reads 13.6 volts. On shore power it reads about 12.1 volts.

Trailer is a 2013 Rockwood.

[JS Stanley]

You are using the solar controller as a battery meter?
If so, it appears that the solar controller is reading incorrectly or has some malfunction when plugged into shore power.

What are your battery readings on a mutimeter after shore power?

[CHICKDOE]

well post #6 pretty much sums it up, the external battery charger is providing a recharge voltage (13.6). the converter isn't. the 12.1 volts is the voltage of the battery. no recharge voltage is going to the batteries from the converter.

so you need to determine why there is no voltage from the converter. possible causes could be:
converter not receiving 120vac inpt power
converter reverse polarity fuses blown
converter damaged
battery disconnect switch has batteries disconnected from converter
resettable 12vdc circuit breaker tripped
loose or corroded battery cable

i would start by taking a voltage measurement at the converter output terminals to see if the problem is on the converter side or in the cable run from the converter to the battery.

[ppine]

thanks to chickdoe.
I got down by the rig controller with a headlamp. The breakers are not labelled, but the fuses are. A breaker was off, that I thought was for the AC. Obviously it contols the feed to the batteries. Now we are charging at 13.6 volts. The batteries are coming up.

Sometimes it helps to stop and think about a situation like this and it is very helpful to have a forum with some smart people asking the right questions. Appears to be fixed.

[CHICKDOE]

new maintenance activity. find out what each breaker controls and label them.

i did it with all my breakers.

[rsdata]

purchase an inexpensive voltmeter form HFreight or Walmart... us it instead of controller voltage to measure batteries...

[johnlochbuie]

Solar will always charge the battery higher the converter

[camaraderie]

Originally Posted by johnlochbuie

Solar will always charge the battery higher the converter

Simply not true ALWAYS. In fact that is frequently not true.

[camaraderie]

Originally Posted by rsdata

purchase an inexpensive voltmeter form HFreight or Walmart... us it instead of controller voltage to measure batteries...

AGREED! And he might as well make it an AC/DC clamp meter so he can track down loads and currents. About $50 on Amazon.

[johnlochbuie]

Wrong it is always true you don't know what you are talking about

[camaraderie]

Since I don't know what I am talking about can you please provide the technical explantion for why "Solar will always charge the battery higher the converter"

I would be interested in being enlightened by your expertise and how it is that your statement is always true. In electrical terms of course. I am not interested in enlightened opinions without facts.

[dward51]

I would bet the lack of a full charge from the converter has more to do with the distance from the converter to the battery, the wire gauge, and condition of the crimp connections which might be exposed to the elements at the breaker on the front tongue area (just before it feeds the battery positive side). Long distance, undersized gauge (for the distance) and crappy oxidized connectors will give you voltage loss.

Couple that with a stock converter which are often "meh" at best, and there you go.

Plus I would bet your solar regulator is probably close to the battery to start with. Higher voltage plus shorter run would mean much better charge. Also did you disconnect the battery to make those readings (if the solar was still connected you are not reading the battery, you are reading the system).

[TitanMike]

Originally Posted by camaraderie

Since I don't know what I am talking about can you please provide the technical explantion for why "Solar will always charge the battery higher the converter"

Let's change the word always to usually for the following reasons.

Converters are usually mounted some distance from the battery and thus there can be a lot of voltage drop.

Solar controllers are usually mounted fairly close to the batteries and voltage drop over the distance is less of an issue. Solar controllers can deliver as much power as they can harvest from the sun directly to the battery while converters are all too often switched to float mode before the batteries are fully charged. Oh they'll eventually get a full charge but it could take several days, depending on battery bank size.

If the solar controller is a Victron Smart controller and it is used in conjunction with a Victron BMV 712, it gets it's voltage signal from the shunt for the battery monitor (via the Victron local network) and the shunt receives it's voltage signal direct from the battery. No voltage drop issues to shut the controller down prematurely.


As for how much power you get from Solar, depends on size and number of panels but unlike a converter, solar doesn't require you to run the generator, or plug in, and as long as there's sunlight it charges, usually quite vigorously from 9 AM to 5 pm.

When boondocking and the choice is to use solar or run generator, I think that Solar is left running longer so in that context, solar will Always provide a better charge to the battery bank.

[TitanMike]

Originally Posted by dward51

I would bet the lack of a full charge from the converter has more to do with the distance from the converter to the battery, the wire gauge, and condition of the crimp connections which might be exposed to the elements at the breaker on the front tongue area (just before it feeds the battery positive side). Long distance, undersized gauge (for the distance) and crappy oxidized connectors will give you voltage loss.

In reality, even if all those faults you described exist, as long as there is a connection between the batteries and converter eventually the batteries will come up to a full charge.

Voltage drop is caused by current flowing (basic Ohms Law). As time passes, even with low current flow, the current will drop as the batteries rise in SOC and so will the voltage drop. As long as there is MORE current flowing into the batteries than they are internally discharging and the external loads are met, the batteries will just think they're hooked to a cheap battery charge that puts out 5-6 amps instead of a 40-60 amp converter. Batteries will still charge, it will just take a LOOOOOOOONG time.

[camaraderie]

I was responding to a post which said something was ALWAYS true (and I was always wrong). Thank you for confirming the errors in that post.