SOLAR and ISOLATOR CONCERNS

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SoCalRob

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Hi everyone!

I hope someone can help clarify some concerns I have for my SOLAR set up as well as my interest in an isolator set up for my battery bank.

Background: I live in a 16' ford transit high roof. I have 4x100W renogy solar setup with 40 amp controller with 4 6v 125 aH wet cell batteries in parallel and series. I only use a fridge full time and it is on the lowest setting (1/5). 

questions?
1. When I am getting a solar charge, I charge at around 1.5-2 amps and approx. 60-70V. While im receiving solar power batteries appear to charge at these numbers but as soon as the sun goes down, voltage goes down to about 12.6V. When i moved into the van, by the end of my first week, voltage had gone from 13.8 to 12.0 v. I have a 40 amp charger I use to charge them over night every few months, but as soon as i unplug it, the batteries Voltage goes right back down to about 12.8v. is this normal? I have read that wet cells resting voltage is typically high 12v's....is this true? 

2. I live in southern california and would like to continue using my fridge through winter this year. I know that there is no way my solar will keep batteries charged up with just a couple hours of true charging power. I have considered a isolator setup to help keep the voltage up on the battery bank. A few concerns on this idea: I hear this can destroy an alternator, is this true? with the size of my battery bank, is an isolator even efficient to charge the bank?  are there any other concerns I should be aware of when using this set up to charge?

I am open to suggestions and hope someone can help me out!
I am no electrician and simply installing solar was a learning curve for me! please be thorough and patient with me.  :D

THANKS!
 

jimindenver

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There are two false readings you will see on your bank, One is while under load, the other is while being charged. Turn off the load and the voltage will rise. Stop charging and the voltage will drop. 12.8v is generally considered fully charged but you need to wait 24 hours to let the bank rest. A better way of seeing the state of charge is with a hydrometer.

With a isolator you would run the truck early to get a fair amount of the bulk charging done and let the solar finish it off the rest of the day. The solar and the Alternator should not interfere with each other.
 

Weight

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A large house bank of deep-cycle batteries will put a large load on the alternator. But I bet the alternator regulator quits before that and cuts it back.
 

John61CT

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You should be able to get more power output from the panels by tilting, and maybe getting a better quality MPPT controller.

Make sure keep them clean and zero shading, not even a twig or bird poop, makes a big difference.

A small gennie may be better than idling your vehicle engine, and I recommend a SoC monitor like SmartGauge or Trimetric.
 

John61CT

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Isolator usually means diode-based, old tech, voltage drop issues.

Combiner, ACR, VSR are more modern versions.

Do nothing for charging other than "joining" the two banks based on voltage above say 13V, and otherwise protecting Starter batt from discharging from House loads.
 

frater secessus

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SoCalRob said:
1. When I am getting a solar charge, I charge at around 1.5-2 amps and approx. 60-70V. While im receiving solar power batteries appear to charge at these numbers but as soon as the sun goes down, voltage goes down to about 12.6V.

400w is plenty to run 12v fridge and other non-intensive loads (nothing crazy on inverter). 1.5a @ 60-70v is 85w-135w of output at the battery.

That scenario sounds like a bank that is fully charged most of the time rather than a problem. What looks like an underperforming system could be one that is loafing along because there's not much to do. You could test this by adding a big load when it is in float to see how high you can spike the controller's output.

SoCalRob said:
of true charging power. I have considered a isolator setup to help keep the voltage up on the battery bank. A few concerns on this idea: I hear this can destroy an alternator, is this true?

Alternator + solar charging is a great combo and the isolator/solenoid/whatever is a good deal cheaper than the solar investment. :) 400w solar

Idling the engine to run the alternator for charging is, IMO and according to SternWake, what causes house-charging alternator failures (overheating). As long as alt charging is done in the course of normal driving you'll likely be golden. Combined charging loads can be avoided by using one of the smarter isolators that John refers to; I use a Battery Doctor isolator that waits until the starter battery has recovered before connecting the house battery.
 

SoCalRob

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jimindenver said:
There are two false readings you will see on your bank, One is while under load, the other is while being charged. Turn off the load and the voltage will rise. Stop charging and the voltage will drop. 12.8v is generally considered fully charged but you need to wait 24 hours to let the bank rest. A better way of seeing the state of charge is with a hydrometer.

With a isolator you would run the truck early to get a fair amount of the bulk charging done and let the solar finish it off the rest of the day. The solar and the Alternator should not interfere with each other.

Thank you for the info!!
 

jonyjoe303

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You have 400 watt solar and 250 ah battery bank. You mention 40 amp controller is that mppt or pwm? Lying flat on your roof your panels should be putting out a least 20 amps, so when I read you only see 2 amps that tells me something is not right. Also solar panel output of 60/70 volts could mean different things, but what is more important is what is the voltage that your battery reads when its connected to solar, it should at least be 14.4 volts to get a good charge. 

You only see 2 amps when the controller thinks your battery is full. A battery that is going bad and has lost capacity will charge quickly up to 14.4 volts then go to float, but it mostly only has a surface voltage as soon as you disconnect the solar it drops to 12.5 or 12.6 and then if you put a heavy load on it will rapidly drop around 12 volts. I think your battery has lost capacity.

Also if you are using a large house refrigerator (110 volts) even a 250 ah battery bank might not be enough to keep up with it. If you are regularly seeing 12 volts on your battery bank, thats not good. You shouldnt be draining it below 12.1 volts (which is 50 percent). 

I recommend you get one of these coulomb battery meters (cost 22 dollars) and connect it to your battery, I just started using these and now I don't have to guess if my battery is getting a full charge. You program the battery capacity and what it does is it keeps track (counts) of all amps going in and out of the battery. If you use 20 amps the previous day, then you know tomorrow you need to at least put 20 amps back to the battery. It will tell you if your battery is bad, if you fully charge your battery and after taking 20 amps out it reads 12 volts its bad (you would have to drain over 100 amps to get it to that low voltage)
You can also use a dc wattmeter (shown on top of coulomb meter) to track capacity but it only tracks to 60 ah but thats enough to check for a low capacity battery. A bad battery will drain quickly.
a coulometer.jpg
 

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