small off grid system

Hi, I have set up a small solar array for my off grid cottage in central Ontario, Canada. Currently I have four 100W panels on the roof (facing south) wired to an MPPT controller, and two AGM deep cell batteries. I am running a Unique fridge (full size) that was designed to run off 12 or 24 volt power. I am keeping to 12V for now. Aside from the fridge we have an inverter 1500W IIRC to run lights at night and also some 12V lighting for when I don't have the inverter hooked up.

I have both the inverter and the fridge hooked up directly to the batteries. My question is, I am in danger of ruining the batteries that way? The fridge draws power thru the night and while generally the battery voltage stays high, but I worry after running all night if there is a dark day batteries may drop below what is healthy for them.

Any thoughts?

Also, if I were to add in another battery, would that give me more reserve power?

Thanks

Dave near Denbigh

That is a large inverter and will self consume a lot of your stored power. Get out your inverter manual and see what the idle power draw is and if it fits into your power budget.

Thanks Mike, I was worried about the idle power draw from the inverter and keep it disconnected (not just turned off but physically disconnected from the batteries) when I am not using it. However I usually have it hooked up from about 7 to 11 PM. I think the manual says it will draw 1 W per hour when idle.

Dave

dnshowell1 said:

I have both the inverter and the fridge hooked up directly to the batteries. My question is, I am in danger of ruining the batteries that way?

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Yes, any time you have something connected directly to the battery you run the risk of damaging them.

dnshowell1 said:

Also, if I were to add in another battery, would that give me more reserve power?

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Yes, adding more battery(s) will give you more reserve, but it really comes down to: do you produce more power than you use? If the answer is yes, as long as the battery(s) have enough reserve to get you through the night to then next sunny day, you will be fine. If the answer is no, then it doesn't matter how big your battery is, eventually you will run out of power storage.

Thanks for that answer. I only hooked up a new MPPT controller a few weeks ago and have only monitored it over the one weekend. That being said, on a partially sunny day I was hitting 100% charge on the batteries by noon (peak sun in my location is about 9:00 AM to about 2:30 PM). So it seems that I could be charging the additional battery "space" without much problem. I am also looking at mounting two more 150 W panels which would add to that.

Thanks again

Dave

iamrich said:

Yes, any time you have something connected directly to the battery you run the risk of damaging them..

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What does this mean?
This makes no sense to me. Without connecting to the battery(ies) you don’t have any power so something is always - at some point- ’direct to the batteries’ especially inverters.

Hi 12Volt - not an expert obviously but most MPPT controllers have a "Load" connection where the draw from applications is regulated through the controller and if the battery charge drops below a certain threshold the feed is interrupted to protect the batteries. I also assume that the fancy all in one controller/inverter/kitchen sink boxes (which I can't afford) have the same sort of safe guard.

The problem with the MMPT load hook up, if I understand correctly, is they can't accommodate loads with a heavy start up draw, like a fridge or an inverter - they just cut out.

I am sure somebody can explain this more eloquently.

Dave

dnshowell1 said:

The problem with the MMPT load hook up, if I understand correctly, is they can't accommodate loads with a heavy start up draw, like a fridge or an inverter - they just cut out.

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Which MPPT SCC do you have? I am sure they are all made a little differently and have different tolerances. Have you looked at your MPPT's manual for its limitations/specifications?

I bought a OOYCYOO 60 AMP MPPT - it was cheap. My rule of thumb for my cabin is don't buy anything that you can't stand to have stolen. A lot of the people in the area (not all - there are good people) like to "hunt" using prybars. The "local" police are about two hours away and their main focus is handing out speeding tickets on highways further south. So I tend not to buy top of the line equipment.

On the plus side the OOYCYOO installed with absolutely no problems. The manual was a bit of a joke, though. I will review it again this weekend to see if I can find anything on the load limit.

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@dnshowell1
I do not use the (often very low A) DC out on charge controllers.

I have a blue sea 12 fuse box connected direct to batteries with 6 gage welding cable and a 30 or 40A fuse on that. I never expect to have anywhere near 30A of 12V although the panel is rated 100A

My inverter cuts out at 11.2V but it’s only ever done that when I was running on junk 10 year old lead acid batteries. (Which strangely did great for a long time!)
I actually haven’t seen it below 12.V since buying new batteries. I *could* run it that low I suppose if I ran the shop vac for an hour at night but I intentionally do all high-current stuff before 2pm. The shop vac usually shows like 900W on the inverter.

A properly sized solar system with adequate input watts should never be a concern. Just like NOT doing stupid things with your car so you don’t wreck it you just don’t do stupid things with your batteries.

iamrich said:

Yes, any time you have something connected directly to the battery you run the risk of damaging them.

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12VoltInstalls said:

What does this mean?
This makes no sense to me. Without connecting to the battery(ies) you don’t have any power so something is always - at some point- ’direct to the batteries’ especially inverters.

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If you connect something directly to the battery, it has a chance of draining the battery to zero (which will kill most batteries). In the original post above, the OP says the fridge and lights are connected directly to the battery. Most setups have an inverter or all in one or some other kind of device that has a low voltage shutoff to protect the batteries.

iamrich said:

If you connect something directly to the battery, it has a chance of draining the battery to zero (which will kill most batteries). In the original post above, the OP says the fridge and lights are connected directly to the battery. Most setups have an inverter or all in one or some other kind of device that has a low voltage shutoff to protect the batteries.

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Got it.
I just always glance at the volt meter occasionally and its always good so I don’t even worry about it.
I wasn’t thinking from the perspective of voltage depletion from over-use. I was thinking literally ‘direct to battery.’

In my case I planned to have sufficient W and it is working. After installing the mppt I’m almost always 12.7+ in the AM and 13.x after sun up.