Wednesday, September 11, 2019
I put a lot of thought into various improvements to my rig, but the one I'm proudest of is my addition of solar panels. I get a lot of compliments. I've also heard some criticism that I wasn't meant to hear, suggesting that two 100 W panels is overkill for a single battery. Well, it is. I have a second battery installed inside the living space, and that's the start for some of the troubles I'd like to help you to avoid.
I bought my panels as a kit from Renogy, which seemed to be the most reasonable and well-documented. All told, the kit, including wiring and the charge controller, was about $130 and the second panel about $100 - all probably more now, since these have been in use for a couple of years. Things have gone great, and I've never even wondered about losing power, and that's with running my furnace off the grid for days at a time, and recharging lots of electronics or even watching TV/streaming - another mod I'm proud of.
So, to the issues - the final one of which I've only just now figured out (I hope)!
First off, my second battery is not identical to the first. I found a space indoors and read that I could install a "sealed" battery there without danger. I didn't want a battery bank, preferring instead to have the peace of mind of a second battery "in reserve." Plus I can segregate my power inverter to the battery charging from the solar panel, to leave the main house battery alone which can be really helpful when taking care of high amperage tasks, like running power tools, or my computer.
But I didn't realize a few things about the charge controller: first is that it has different profiles for different types of batteries, and so I had to switch the controller each time I switched the battery being charged, or so I thought. That may have introduced a few glitches.
Second, cheap solar charge controllers all seem to have an equalization phase, which boosts the voltage above the max to deliberately boil the electrolyte, which is apparently good for the longevity of the plates.
When the igniter board on my water heater fried, I had an inkling that it might have been the solar setup, but I couldn't quite figure out why. I scoured my work for bone-head configuration or shorts. Now I realize that my internal electrical system doesn't include this equalization phase in its charging profile, making plug-in a much safer way to treat a battery if you don't know when its voltage might rise and fry delicate electronics.
I remember using a cheap charger at home to float a charge on the RV battery during the winter, and then hearing the battery boiling, only to find that the charger was doing its equalization thing, which I don't think you really want during storage. That charger had no setting to disable that.
To be fair, the solar charge controller includes in its documentation the warning not to have ANY load on the battery while it's in equalization phase, and somewhat separately a warning that to do so may damage sensitive powered equipment (presumably like igniter boards). It all becomes clear in retrospect.
It's hard to find good information on this stuff. It's also hard to keep all the variables in mind. A look at the specs of the water heater igniter board indicated an upper limit for voltage that was far below the upper limit on the charging battery with the solar system, and so perhaps it fried while I randomly turned on the water heater while the solar panel was hyper-charging. Bought a new board and it soon fried. I was inhabiting the trailer during the day, as it was winter, but I couldn't connect the dots.
Trouble is that there is no indication on the controller about when it's in equalization phase. I installed a voltage readout (for about $.50), but that clouds the issue since the "boost phase" seems to pump up every morning to above the limits of at least those old fried igniter boards, and it's not so easy to distinguish between boost and equalization from voltage alone. (the on-board plug-in charger never seems to pump that high)
I solved the water heater igniter problem with a much more robust Dinosaur board which had a broader range of acceptable voltage (I've kept the old boards and will look for how to repair them - probably a single component needs to be replaced?).
Then a new issue cropped up out of nowhere. Apparently after aging out a little the internal battery started to bleed enough hydrogen to set off the propane alarm which is right beside it. Since the trace amounts of hydrogen seem to linger, and since I didn't understand that propane detectors detect most anything remotely flammable, and especially since when I did have a propane leak that I could actually smell it didn't go off, it was really tough to track down the issue. I guess my nose for the stink they put it propane is more sensitive than the detector??? Maybe pure hydrogen sets it off in much lower concentrations than propane needs. Yeah, that's probably it.
Interestingly, I had been charging the internal sealed battery while driving, supposing that the flooded battery outside the RV would be charging from the car and I'd have two topped-off batteries at the end of every day.
The propane alarm never went off.
But then I found that the external flooded battery, which was running the refrigerator, never quite kept up its charge from the car's charging system alone. I think there was just too much length of wire from car circuit to fridge, and the 10 Amp - 80 -120 Watt - or so draw over-offset the charging. It was when I decided to attach the house battery to the solar panels that the propane alarm started to go off, but only when the trailer was left sitting without me running anything and I'd reverted the solar panels to the internal sealed battery.
I still don't understand what's going on, but here's my theory: There are at least three chargers in my setup. One is the car, two is the internal power center of the trailer which charges when plugged into shore power, and three is the solar charger. It seems that a second charger prevents the solar controller from entering boost mode, since the battery voltage never drops far enough. Ditto the car charger. I had been worrying about charging profiles, which seem deceptively important on the solar controller where battery type can be selected. I should have just been worrying about voltage curves over time; neither the car charger or the on-board power center know anything about battery type, or if they do the car is tuned for starting batteries and the power center is tuned for deep cycle flooded (versus sealed) batteries.
I like having the solar panels connected to the house battery while driving since I don't have to worry about the fridge draining the car battery if I stop too long for lunch, a nap, a stroll or whatever (although that never happened before I "understood" so much. Ignorance is the best fix of all, for sure). I know I could install an automatic cutoff switch between trailer and car to preserve the car's battery, but one has to draw the line somewhere. . . ha!
Anyhow, my internal sealed battery is simply out of the equation now most of the time, reserved as a spare, and I tend only to charge it while stationary by using the solar charger. That pattern, or the aging of the battery, has led to the alarm going off, perhaps because the battery is always ready for boosting when I switch the solar panels over to it. The boost seems to keep going for some set time, need it or not, and so some hydrogen boils off through whatever pressure valve there is.
I can find no documentation about how to track the equalization cycle which is supposed to happen every 28 days on my solar charge controller. My question is, does the calendar reset each time I swap battery types, or if the battery is disconnected? Am I always accelerating the cycle when I swap? That could explain things. But so could the simple triggering of boost voltage, which seems to happen each time a rested battery is reconnected to a charger.
I think I only need to worry about finding a voltage below what will cause the internal pressure of the sealed battery to exceed whatever the relief valve is set to. I know for sure that the el-cheapo solar charger pumps out uncomfortably high voltage, which my meter likely mis-overestimates since the charge is actually composed of pulses of the panel voltage to approximate a lower voltage, and which my meter may mis-read.
So, my solution is to purchase a second solar charge controller, to get one for each battery. The new one is an MPPT controller, and more expensive at $100 vs. $30, but it's supposed to be more efficient by regulating amperage rather than to just pulse full voltage as the cheaper PWM style does. The main things is that it has a configurable profile and so I can disable equalization and or boosting altogether for the internal battery, as well as set the boost and float voltages.
So far that's done the trick! I'm still allowing it to boost in the morning to a lower set-voltage and I put the float down near where the on-board power panel is. No boil-off! And I consider much if not all of my theorizing to be validated.
I know that the on-board charger has the advantage and is designed around the notion that the battery will never be drawn down while plugged in (you can even disconnect it without the lights even flickering), though it will jump up a few tenths of a volt if something does draw it down (like my inverter, which is isolated from the house current).
The remaining unknowns are whether my first solar charge controller is somehow off-spec through wear or my fumbling. That might be why it started to overcharge the battery. But it does read pretty close to spec. I guess that solar setups assume near constant draw on the batteries before the house goes to sleep and so the charging voltage is set relatively high? And so the other unknown is whether I'm damaging the external battery by leaving it on the cheaper charger.
I do now have the new benefit of having re-configured my switch to swap the solar panels and not the batteries, which should be safer for the controller electronics, since they don't like being attached without a battery; the incoming voltage spikes, apparently, enough to fry the controller.
Plus I have the added benefit of just cutting off the solar panels altogether with the third position on my switch in case I'm plugged in.
I'm guessing I could have solved things by reverting to my old ways and/or making the internal battery the default house battery and keeping it off solar. I could also move the propane/CO detector away from the battery or vice versa, but then I would be placing things sub-optimally and making new holes, etc.
Way too much thinking, but perhaps it will help someone else who's facing similar conundrums. I'll document below the mods I've made in case you, fictional reader, may find them useful. I've spent so much time pondering this overall issue that I'd like to save the next person some time. None of the pieces fit together easily or quickly for me, but I think I may finally have a solid theory and I'm sticking to it!
There's lots of advice out there, but little enough explanation at a level to allow you to solve my own particular issue. Hardly anyone seems to get into it so deeply.
Posted by Lex at 1:00 PM