Since my charge controller is playing silly buggers on me, I was looking at alternatives today while also looking at what exactly constitutes a flat battery.
My battery is a 35AH Thunderbolt Magnum 12V Deep Cycle battery. It’s referred to everywhere except on the battery as being AGM but it looks to me very much like it’s just a SLA. If it was AGM, it would say so. There are both raving and castigating reviews online which really doesn’t help much. In fact most online reviews I have learned to discount as they have a high degree of subjectivity rather than objectivity. Those with the most detailed and objective negative review just seem too fake to be believable. That’s the other thing - if it sounds unbelievable, it really isn’t believable.
I just measured the battery after sundown at 13.1V. That’s quite high as I understand SLA batteries are at 100% charge when the voltage reads 12.7v to 12.8v. They’re at 40% charge which is the lowest recommended charge at 11.9v. By the time they reach 10.5v they’re so flat it’s not even funny and have probably been damaged by the depth of discharge.
There seem to be two types of battery charging - PWM and MPPT and reading up on these it seems that PWM pulses power from the solar panels to the batteries. I’m not sure why that would be and it seems pretty strange. The more charge there is in the batteries, the longer gaps there are between the pulses and the shorter the pulse. That just seems an utterly strange way of doing things to be honest.
MPPT seems pretty complex at first then just gets ever more bizarre. I’ve read the descriptions enough to know what’s going on but it just still seems bizarre. They’re also pretty darned expensive! One day I might try one but don’t bet on it! It could be that the descriptions as to how they work are just extremely badly put together. Technical people largely seem to have no command of the English language.
My charge controller is still going nuts even though I now have a .1 microfarad capacitor on it. I’ll try it with a 1 microfarad and see what happens. I have a feeling the charge controller is the problem and my research today has involved various things up to and including doing without charge controllers.
At its crudest level a high-voltage cutout is what’s needed to stop a solar panel wired directly to the battery from overcharging the battery. A low voltage cutout is all that’s needed to stop a battery from being discharged too deeply. The rest is all fluff.
If one checks the voltage regularly - note that I have a voltmeter on every USB station in the bus - then there’s absolutely no reason to go below 50% on the batteries. In fact I’ve seen a charge controller that is just that - it controls battery charge level without touching the battery use side. Thus a battery can be charged without an included low-power cutout. That actually sounds far better than what I have right now.
As far as the battery is concerned, those 35 amp hours don’t seem to be all that much to be honest. In theory at 40% maximum discharge those 35AH should give me 21 usable AH of power. That means my twin fans consuming 2.5A each should run for just over 4 hours before cutting off. I’ll bet you they won’t though! I’ll program my charge controller to cut out at 12v one day and will run those fans just to see how long it’ll run before they cut out. My betting is considerably less than 4 hours!
So, it looks like I have two options ahead. First I can get just a plain Jane charge controller and say to heck with an automated power cutout, relying upon my voltmeters instead or I can get an MPPT controller. Perhaps even just say stuff the fancy Nancy stuff and go for a basic overcharge preventer and over discharge preventer.
It sounds as though the MPPT does a half-assed job with the charging. It sounds as though it does a bit better than the PWM controller but that’s not saying an awful lot. PWM just seems utterly strange - it takes the solar panel output, throws away anything over 14v and supplies just 14v at the amperage coming from the panel. MPPT concentrates the (for example) 19v and converts it down to 14v but outputs it at a higher amperage. That sounds fine and dandy but when your panel might in poor light be producing 9v, it’s still throwing that away rather than boosting it to 14v but at a lower amperage.
It looks like I need to do something. It could just be that the charge controller I have is junk. I’ve been through several cheap Chinese charge controllers but then I’ve not yet come across anything that’s made in the USA yet. Half of the stuff sold as “USA made” is actually made in China but assembled in the USA. It’s as though they buy the same cheap crappy charge controllers that I can find on ebay and then put them in a fancy package and charge ten times the price. I would not put it past them to do this. As the new trendy technology, all the sharks dive in and start flogging junk at high prices. It happened with computers then mobile phones then tablets and now it’s solder.
Well, my bank statement comes in a few days so I’ll be able to see what I can afford. I might try one of the MPPT controllers if I can’t get my current controller to play nicely with the fans. I’m between a rock and a hard place there. The LED controller won’t charge the batteries fully and won’t cut the power when the battery gets too low. The LCD controller throws a wobbly when I start my fans.
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