Off grid solar system for maintaining half a dozen batteries (ATV's, tractors, boats, etc).

[sobee]

Thanks everyone!

1) Is it possible to buy buck converters that are "certified" e.g. CSA, ETL, UL, etc.? I'm wondering about insurance implications? If I'm not going to be able to make the insurance company happy, I guess I could look at putting "non-certified" electronics in a cabinet that reduces my fire risk. I have no idea what that would look like, but I imagine they exist.
2) @GXMnow Can you elaborate on the purpose of the capacitors? I understand the diodes.
3) I suspect I could find "certified" PWM charge controllers that would be more "insurance friendly". However, I haven't found a charge controller that is very user friendly. They all seem to require you to disconnect from the solar supply before disconnecting from the battery and vice versa when reconnecting. It sounds like they get buggered up easily or switch to 24V charging if you don't do things correctly. I really want the ability to remove alligator clips before I mow, and reconnect them when I'm done mowing without having to reprogram things or reconnect in a certain sequence. Is there a charge controller that would allow this?

 

[GXMnow]

The capacitor is to handle the current spikes from the PWM buck converters. A solar cell is not a stiff power source. Any current is going to cause the voltage to drop. And with multiple PWM buck converters all running at higher frequencies, that could cause an issue with them fighting each other. If you put a 10,000 uf capacitor on the cell, it may take a minute or so for it to charge up to the VOC voltage, but it will absorb the pulse currents and keep the voltage fairly stable.

If you truly want safety certified gear, then I would go with the off grid setup with a main charge controller and battery bank, and an inverter running battery maintainers. Then you can get all UL, ETL, or CSA rated equipment. I did a search for UL listed solar charge controllers, and there are not as many as I would have expected. A UL listing does not mean something is good, it only means it is safe. Even if it fails, it won't start your house on fire etc. I was building installed sound systems, and we brought in some amplifiers to get tested, and they kept failing them. The power transformer was just too tough and would not fail. They replace all fuses with solid copper bars, and short the output of the power supply. Of course it just tripped the 20 amp breaker. So they put it on a 60 amp breaker, and then the power cord burst into flames, DUH! The UL listed version of the amp, now has a built in weak spot in the transformer primary winding. This way, even if an idiot bypasses all the safety features and plugs it into a 60 amp circuit, it just makes a little pop, and the 40 pound transformer is now a piece of junk, but there is no fire. SAFE!

I did find a Go Power brand 30 amp charge controller with a big banner (Now UL listed!!!) I can't say if it is any good, but it is "Safe"

 

[rin67630]

Here we go with your 100W panel obsession again. Everything with you is about 100W panels and even though you calculate they are inadequate for this job and one you have yourself, you refuse to even acknowledge the existence of larger, more powerful panels or the possibility of using more than one to increase the available power.
.
YOU are the only person that keeps banging on about pissant 100W Panels as if nothing else can be used.

Could you please refrain your aggression?
I did not insult you.
One needs a reference to make comparisons and if you don't compare what is comparable every discussion is vain.
With you it is anyhow. Bye.

 

[rin67630]

However, I haven't found a charge controller that is very user friendly. They all seem to require you to disconnect from the solar supply before disconnecting from the battery and vice versa when reconnecting.

The battery is the "power-supply" of the SOC, without it, it mainly cannot function correctly, and will have an erratic behaviour.
In some configurations, without load you might easily get to higher voltages.
As long as you keep using a <24v Voc panel (or more in parallel) it is very unlikely that disconnecting the battery will destroy the SOC.

 

[sobee]

I find this topic quite fascinating and I appreciate all the ideas!

I have no background at all with buck converters.....are they pretty low fire risk?

If I went with an inverter and battery bank, how many batteries would I require? Is there any chance my Marine battery for my boat could run the whole show adequately? The boat is only out of the shed 2 to 4 times a year, so given that it is sitting around most of the year, I could put the battery to use in the solar system. I think it is a group 24 battery, so it is the same size as a car battery. It's a small fishing boat. Battery was around $100 US. I suspect that is pretty small.....but if I'm just charging batteries, then maybe? Am I dreaming?

Please humor this dumb question. Do the invertors have logic to shut down once the battery has discharged to a certain voltage? Does it simply turn off? I wouldn't want to "freeze" the marine battery by drawing off too much power during a cold night. Is there any way to estimate the safe amount of discharge, and how many amp hours that would equate to? That would allow me to calculate how many batteries I would need. My AC trickle charger is drawing 10W when I first plug in, and it is down to 2W by the next day. I have the "power consumption" meter now, so I can get some real numbers.

 

[rin67630]

Please humor this dumb question. Do the invertors have logic to shut down once the battery has discharged to a certain voltage?

What are you calling the "invertors"?
Any decent SCC will have a circuitry to shut down once the battery has discharged to a certain voltage, dumb buck converters will not.

But you just want to trickle charge batteries, so the risk of discharging to a certain voltage is cared for!

 

[GXMnow]

The boat battery is likely enough energy storage and should work fairly well. But check the labels on it and see if it is rated as deep cycle or starting etc. A Deep cycle battery is better as they have stronger plates that can handle being pulled down to 50% many times. A starting battery is built to handle a big surge current, but then get charged right back up. A deep discharge on a starting battery will shorten it's life. That said, you can probably set it up to not have to deep cycle. Have you been able o measure how much power is needed for the battery maintainers?

Have a charge controller keep the boat battery charged. Have a timer power up an inverter to run the maintainers for 4 hours each day while the sun is up. That way you are not asking the boat battery to run them all night. I have used a battery tender maintainer to keep my jump starter pack topped up. After I use it, I plug it back in, the light stays on for maybe an hour, then it goes to pulsing in the float mode again. As long as they reach float each day, or even a day or two each week, they should live through the winter.

 

[sobee]

Thank you. I thought all marine batteries were deep cycle. I guess not. I checked mine. It is a starting battery. 675 MCA, but deep cycle is not mentioned. Went to their website and I see it would have cost me $10 more to get a deep cycle with similar spec's.....wish I had known.

If I go forward with this project, I will need to buy half a dozen AC trickle chargers. My old one draws 10 W initially and is down to 2 W after 24 hours. I have no idea what the new one will draw. This sounds like the perfect excuse to buy one and give it a try

 

[GXMnow]

Even with all 6 pulling 60 watts, should be no problem at all. If you are going with the charge controller and marine battery, I would step up to a 300 watt panel. Even at the 1.9 sun hours in a Canada winter, you can still get 500 watt hours a day. Have a timer turn on the trickle chargers for a few hours a day. Watch how well the marine battery is holding up and see if you want to run them more or less. If all 6 do idle down to just 2 watts, maybe they can run 24 hours. You should have about 20 watts available all day. It also does depend a bit on how efficient the charge controller and inverter is.

 

[sobee]

I just realized I have a 600W modified sine inverter in the closet.....that opened up the possibility of doing a test! Are these "car type" invertors suitable being used in "continuous" service in a solar project? It isn't rated for freezing temperatures and -35 to -40F are in play.....

Here is a bit about my test. The marine battery tested at 12.89 volts (after sitting on the bench for a week). I connected the inverter to it, and the trickle charger to the inverter and to an ATV battery. After an hour, the marine battery voltage had pulled down to 12.49, but when I disconnected the inverter and waited 5 minutes, the marine battery voltage had climbed to 12.62. Everything is disconnected, and I will check the voltage in 24 hours. I'm not sure how long a person should wait?

Would I be correct to assume that it is safe to discharge this battery down to 12.42 volts, which I believe is still 80% charged? If so, I will run the experiment for longer till I find out how long I can run that particular trickle charger on the marine battery.

I'm also curious if a deep cycle battery is truly an advantage? Temperatures in my shed will get down to -35 or -40F occasionally. I was looking at some charts that suggested I need to have at least 12.4 volts to prevent electrolyte freezing at these temperatures.

I've ordered another trickle charger. I'm expecting it might be more efficient as it has microprocessor to control the charge and I'm expecting it might jump to float quicker than the old trickle charger I'm using.....hopefully. I'm not sure if it is wise to run this new trickle charger on a modified sine inverter due to the micro-processer. One reviewer said they had no problems so I will give it a try.

 

[GXMnow]

I would have to look it up, I don't remember the 50% discharge voltage on Lead Acid. Anyone watching know this off hand?

 

[sobee]

I agree....it definitely is a lot more complicated than Buck Controllers. I may still go that route; not sure. I'm not sure how to quantify the risk or even what the risks are with using uncertified equipment and insurance companies. Google tells me that fires/smoke do happen with buck converters. So it is a real risk. Having said that, if I google battery chargers and fires, there are a lot more hits. If I go the latter route, I get insurance if there is a fire.....

I also agree with your sentiments about the weather. Electrolytes can and do freeze on a really cold nights up here. The freezing point of an electrolyte is a function of the amount of charge. I already did some calculations before that last post, and I believe that I'm good if I don't pull the battery voltage below 12.4 volts. I used the charts at this web page to calculate this. I used the following chart to see what percentage of drawdown that would be on the battery and it is around 20% drawn down at 12.42 volts. I probably don't want to discharge a "starter battery" below that. And maybe that is too aggressive.

That battery recovered to 12.81 volts after I let it rest for 24 hours. This is the battery that ran the inverter and a trickle charger for an hour.

 

[rin67630]

Again, Sobee, there is really no need to over complicate.
Having batteries fully charged and tested over a week at the beginning of the winter are requiring the very minimum to keep them trickle charged to 13,8V and let them pass very deep temperatures.
At their trickle voltage you will not need much energy, you can put them in (fused) parallel as long as they have the same voltage and chemistry.

The less stuff you have involved, the less risk you will generate and the less stupid questions an insurance will ask in case of fire.
That was my final post on that topic.

 

[sobee]

Thanks Everyone. The new AC trickle charger I bought draws 0.5 W when it goes to float. I had it on three different batteries and it went to float very quickly. Thus, it is much less power draw than the old one.