I’ve been frustrated by my newly-rebuilt electrical system. It holds its own under maximum load, but doesn’t seem able to fully charge the batteries even when I switch everything off and leave it off for all of a sunny day. I’ve yet to see the batteries reach much better than 13 volts. The batteries are used six-volt 186 amp-hour flooded lead-acids and they seem fine, but I don’t know how old they are and they were low on electrolyte when I got them so it’s possible they’re a little sulfated.
Mostly I think it’s just that I don’t yet have enough solar panel, but I really wanted to see how the system behaves when the batteries are fully charged and I just didn’t seem able to get them there.
Yesterday I got a wacky idea. Just over the ridge there’s a solar power system that’s much meatier than mine, and fully-charged. My friend Silver sent me a Battery Minder a couple of years ago that can probably bring my batteries up to charge and desulfate them if needed. If I could connect those two things to my batteries, I could maybe recondition them and see what happens then!
Heh. I’m not above redneck engineering.
It happens that, here and there, we’ve got a helluva lot of extension cords. My long one is already over at M’s Dome, where I brought it to run the hammer drill earlier in the week. So I made the rounds and collected every single heavy cord I could find. I stretched them all out from M’s front door, over the ridge to my power shed.
I was less than two feet short. I am not making this up.
Went back to M’s Dome. There has got to be a way to do this. Right then the cord stretched all the way to the front of the Dome, around to the door, in through the door, and plugged in at the kitchen. Lots of waste there. Short cut anywhere?
I looked up at his (not currently connected to anything) chimney.
I went and got a ladder. Disconnected the plug. Coiled up the cord, climbed to the roof, dropped the cord down through the chimney. Went inside, plugged it into the nearest outlet.
Yup, that saved me a good three feet. And sonuvagun, since the Battery Minder doesn’t really need much power that 400+ feet of power cord will fire it up.
Heh. Now we’ll see if the batteries will charge.
Sometimes “redneck engineering” is the very best kind. Other times it can get you killed 🙂
I’d love to know what the voltage is at the far end of the 400 foot extension cord. 100vac? 90?
I really don’t want to know, Woody.
Under performance of PV systems can usually be traced to: 1 Long cable runs from panels to battery and/or under-sized conductors. 2 Shade, even small amounts of the panel being shaded during the day. 3 The charge controller being set too low, it should be 14.4-14.8 volts to fully charge the battery. 4 Poor orientation of the PV panels. Even with good orientation of the panels you are lucky to get the equivalent of four good hours of charging. That is a 100 watt panel producing 400 watts a day. More likely you are getting 250 watts a day from a 100 watt panel. 5 A loss somewhere in the system. Either something is connected to it and not shut off or something you know is in the system is running at poor efficiency. A typical inverter may only be 85% efficient and even when you aren’t using it the thing is wasting energy. Even your charge controller can be eating your watts. 6 Your batteries. Simple as that. Your batteries seem good but they are not. 7 Discharging your batteries too fast, i.e. you are running something that is too big (in terms of consumption) when you use it and your batteries discharged too fast (or too deep) and will not recharge fully in a reasonable amount of time.
1: Nope, cable runs are minimal. Panel-to-controller is less than 20 feet.
2: Shade was a problem before the rebuild, but is now not a factor.
3: Charge controller is set to 14.4V, verified by two people more knowledgeable than me.
4: Orientation is not perfect but not terrible: They lean due South at (mumblemumble) angle.
5: Nope. This system is simple enough that parasitic loads are easy to track down.
6: Possible: Working on it.
7: Well, duh. That’s what I’ve been sayin’.
Having said all of the above, I confess I don’t know how much of a parasite the inverter is. Before going to the current expedient I switched it off during the day for a couple of days just to see the effect on battery charging. The effect, if any, was not measurable.
The problem with trying to fix this problem is without knowing for sure what is wrong it could cost a lot simply because you replace components thinking “aha, that’s what’s wrong!” only to find out it isn’t. A good approach is to make sure everything is correctly designed/assembled first then look for the obvious and work your way down the list.
I do have a problem with your answer to #1. 20 feet isn’t really minimal however may be unavoidable. So what gauge wire are you using? 8 gauge to 3 gauge might be appropriate. This can be calculated or tested with a large resistive load. The calculation is easy but it will miss a poor connection at either end. One of the problems with connections for heavier gauge cable is a pressed connection may not make sufficient physical contact or may have corrosion or other “matter” preventing a good connection. I like solder to insure a good connection.
Are your batteries clean? I mean “Dawn” and hot water and a brush clean. Dirty or damp batteries can drain the charge off.
Just trying to help.
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