Expected voltage drop?

[4x4junkie]

I'll bet that is your problem.
130W (9 amps @ 14.4 volts) is not enough solar to maintain a battery bank that size (I'd bet that your controller never reaches the Absorb charging phase if you're using even just 15% of that bank's capacity each night).

A bank your size needs a minimum of 21 amps of solar charge current (5% of the total Ah figure) to effectively keep sulfation at bay, with 40-45 amps (10% of Ah) being better. This provides enough current for your batteries to make it through the Bulk charging phase so that Absorptive charging can begin while there is still a good amount of daylight left. To reach 21 amps you'll need a minimum 300 watts of solar panels if you use a MPPT-type controller (360 watts if you use a PWM controller).

For S&Gs, I did a similar test on mine (two Delco Voyager (flooded) in parallel for a total of 190Ah, using a load of 4.5 amps)
Starting volts was 12.83.
After 4 minutes it had dropped to 12.57 volts (a 0.26V drop)
After two minutes of rest the volts came back up to 12.78.

So I would say very likely you have a sulfation issue that is just beginning to present itself.

 

[Fusooka]

So is solar an "all or nothing" proposition? Make sure you can produce enough amps relative to battery storage size to achieve bulk absorption or don't bother?

 

[4x4junkie]

Well, you need to charge up your batteries somehow...
To remain healthy, they need to be fully brought up to a 100% state-of-charge at least somewhat regularly. This requires some hours of Absorptive charging (if very deeply discharged, they will need many hours, like much of the day even). It's just the nature of lead-acid battery technology. If this doesn't get done, whatever lead sulfate that remains on the plates eventually hardens into a crystallized form, and becomes very difficult (though not impossible) to return it back into the electrolyte by charging. The batteries don't really care how you do the absorptive charging, just that it gets done. Solar generally lends itself much better for this purpose than running a generator or idling your vehicle's engine for much of the day each day...
A shore charger can provide good absorptive charging too as long as it doesn't "time out" of Absorb too soon, and it's output voltage is set sufficiently high, though of course this tethers you to an AC source... If your trips are generally less than a month long, plugging it in for a day or two each time you come home might be enough to keep your batteries in decent shape.

 

[Fusooka]

So, considering my current setup, what role does my solar charger play in my system? Just maintaining float on a fully charged battery? Based on what you're saying (which is very helpful, by the way!) it would seem I either need to add more wattage to my solar charger or rely primarily on my alternator (sans shore power) for absorption?

 

[dwh]

So, considering my current setup, what role does my solar charger play in my system? Just maintaining float on a fully charged battery? Based on what you're saying (which is very helpful, by the way!) it would seem I either need to add more wattage to my solar charger or rely primarily on my alternator (sans shore power) for absorption?

Depends on how deeply you drain your battery, and how much you drive the truck to charge off the alternator.

But you say you never drop below 12.5v, so you aren't drawing down the battery much.

Each day as the sun comes up, the solar charge controller *should* see 12.8v or so on the battery from overnight resting and then *should* kick into a full 3-stage charge routine - bulk to <dunno what the programmed set point is on your charge controller - 14.4v?>, which won't take long, then drop to absorb at <14.2v?> which depending on the charger and battery state of charge will either last a couple of hours, or could last until the sun goes down.

IF your solar charger runs through the two charging stages - bulk and absorb - and then makes into float before the sun goes down, then it's working and it's enough to get the job done.

At least, enough to get the job done at those particular voltage set points.

If the charge controller never drops from absorb to float, then you don't have enough solar to get the job done in a single day.

However, depending on your battery, and if your charge controller is programmable AND has temperature compensation, you might want to tweak the voltage set points up a bit, like bulk to 14.8v and absorb at 14.4v - float is probably fine at whatever it's set to now, as it won't spend more time in float than however long the sun shines.

Most batteries can be pushed a little harder IF they don't get overheated, and it will help to A) insure a truly FULL charge, and B) help extend the battery's life.

 

[Stumpalump]

Surface charge is not understood even by me but you can think of it like this. Your battery is 100 buckets. Each hold 1% of the voltage. Some buckets hold a cup and some hold a gallon. Empty any bucket and you loose a percent. At one charge level that percent may take a while but on others especially near the top they may empty quick. Electricity may have all sorts of rules and formulas to understand but in real world it does weird stuff. Reading the voltage should only be used as a general guide and not the exact level of charge or amp usage. It will fool you.

 

[Fusooka]

IF your solar charger runs through the two charging stages - bulk and absorb - and then makes into float before the sun goes down, then it's working and it's enough to get the job done.

Good advice. I'll test it...

 

[dwh]

What I finally learned was that my charge controller was too far from the batteries and the wire gauge used was way too light. With the voltage drop across the charge wire the batteries were not getting the full bulk or absorb voltage from the controller, and I later learned that my 200 watts of solar were at best supplying only about 6 amps. So even though the controller and voltage monitor said everything was great my batteries were fast becoming badly sulfated. My batteries seemed to take a charge and check out with a meter, but they were not in very good condition.

That's a pretty common idea. It's not accurate though. It doesn't actually work that way.

Voltage drop is a function of load. The higher the amps flowing, the greater the voltage drop. But when charging, as the voltage of the battery rises, the amperage flowing goes down. As the amperage flowing goes down, the voltage drop goes down. Ultimately, by the time the battery reaches fully charged, the amps flowing are down to almost nothing - and the voltage drop has gone away.

So, having smaller wire or a longer distance won't prevent the battery from reaching full charge voltage.

The charge controller is looking at the voltage on the charge loop, and the battery is what regulates the voltage on the charge loop, until the battery voltage comes up high enough that the charge controller can take over regulating the voltage on the loop.

So if the charge controller sees 14.4v on the charge loop, then the battery has reached 14.4v - regardless of the wire size or distance.

What smaller wire can do, is make it take longer for the battery to reach a fully absorbed charge state.

If your system was reaching the end of bulk stage by noon, that only means that the battery was somewhere around 80% charged by noon. You still had hours of absorb stage to get through for the battery to come up that last 20%.

So it sounds to me like your small wire was adding so much time to absorb stage, that the battery never did finish fully absorbing all it could before the sun went down.


Which is why I said that if the OP's system is getting through both bulk AND absorb stage, and reaching float stage (charging is finished) before the sun goes down, then it's big enough to get the job done.



What most people don't realize, is that voltage drop behaves the opposite when charging a battery as it does when running loads from a battery.

When charging, as the voltage rises and the amps goes down, voltage drop eventually goes away. When running loads from a battery, the voltage goes down, the amps goes up and the voltage drop just keeps getting worse.

 

[4x4junkie]

When I started out with the solar system in my camper van I would often see my MPPT controller indicating bulk stage complete by noon or before. I even hooked up a voltage display at the controller to monitor state of charge. Every evening the meter was showing fully charged batteries. But my batteries performance was degrading within just a month or two. With just light usage overnight, like only 10 to 20 amp hours, by morning my 220 amp hour battery pair were dropping well below 12.00 volts.

What I finally learned was that my charge controller was too far from the batteries and the wire gauge used was way too light. With the voltage drop across the charge wire the batteries were not getting the full bulk or absorb voltage from the controller, and I later learned that my 200 watts of solar were at best supplying only about 6 amps. So even though the controller and voltage monitor said everything was great my batteries were fast becoming badly sulfated. My batteries seemed to take a charge and check out with a meter, but they were not in very good condition.

I don't know if any of this applies to the OP, but his situation sounded much like what I was experiencing. I've hopefully rectified the problems in my own system although I now have a pair of badly sulfated batteries to deal with.

You learned correct, that issue is entirely too much resistance in your wiring between the battery and the charge controller. I won't get into specifics here though as I recall it led to another thread some time ago hitting the skids... But suffice to say the less resistance in your wiring, the better the performance of any charging source will be.

Throw each of those batteries on a desulfator for a week or so, I'll bet they can be recovered. Just make sure no other items are connected to them at the same time, as any other wiring connected to the battery reduces the effectiveness of the current pulses a desulfator puts out.
The OP should look into a desulfator for his as well. Though I suspect the large size of OP's batteries will probably require more time on a desulfator.

I built this little gem here (the "original" version), but I would think commercially-available units should work as well (might just take longer).