Building my first off grid system

cs1234 said:

I think he meant the link you provided defaults to the 20 amp hour battery for some reason when you click it. They do have a 200ah battery available as well, but we can't be expected to look around the page a couple inches and see the 200ah battery available on it!

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Ahh gotcha

Hauls Assington said:

Ahh gotcha

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Yeah, our time is valuable my man! We have solar panels that need their daily wipe downs.

Welp, I am going to leave town for a few weeks, the test will be to see if all the meat is still frozen when I get back.????

Hauls Assington said:

Welp, I am going to leave town for a few weeks, the test will be to see if all the meat is still frozen when I get back.????

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Weird trick... Make sure to also freeze a bottle of water on its' side and then turn it upright after frozen. If the freezer ever gets too warm, the water will flow back down to the bottom of the bottle.

Lilikoi_Heavy_Industries said:

Weird trick... Make sure to also freeze a bottle of water on its' side and then turn it upright after frozen. If the freezer ever gets too warm, the water will flow back down to the bottom of the bottle.

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I use these wireless monitors, but your method is certainly cheaper.

cs1234 said:

I use these wireless monitors, but your method is certainly cheaper.

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Nice... The amazon link looks pretty good!

I'm a big fan of appropriate technology and I consider the silly liquid gravity sensor in that category. I do tech for a living, cloud architecture and security for big organizations, it's really easy for me to get carried away. "appropriate tech" is one way of checking myself. I like to ask myself what the (dis)advantages are when comparing a cheap/free hack against a more complicated or more expensive solution.

If I get tech for the purpose it will probably be ruuvitag, or something that can communicate with VenusOS (OS used by Victron CerboGX), mine is on a raspi4. That way I can monitor/alert on the metrics from the internet on Victron's Remote Monitoring site, I'm also interested in setting up our 10000gallon water tank with a level sensor to put on a house dashboard.

Lilikoi_Heavy_Industries said:

I'm a big fan of appropriate technology and I consider the silly liquid gravity sensor in that category. I do tech for a living, cloud architecture and security for big organizations, it's really easy for me to get carried away. "appropriate tech" is one way of checking myself. I like to ask myself what the (dis)advantages are when comparing a cheap/free hack against a more complicated or more expensive solution.

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I too develop a bit of software.

A frequent thing I run into, is : Do I write the software solution myself or purchase a ready made library that already does that. I'm horribly cheap, but I have to remind myself if a library license costs $300, but saves me a significant number of hours of work, I should probably buy the license and use that. Not to mention, if it's a library that is actually maintained and gets new features periodically, it might save me future development time when related API's and such are updated.

I try to apply that same principle to buying crap like the fridge monitor, for $30 it did what I needed and I'm done with it. I like your Victron Cerbo idea, and it would be cool as heck, but I'm already stretched so thin. ?

Make vs. Buy

I recently purchased an EMI test system for work, "Bulk Current Injection". This uses a clamp transformer to inject common-mode current in system cables, emulating what happens when RF passes through. System is then examined for upsets.

It is "Rack and Stack" of off the shelf instruments, plus split transformers and calibration fixtures.
I could have written the software, fun project. But compared to $2500 software purchase from vendor, would have cost my employer far more in salary. And a supported product is better to hand off for others to use.

The purchased software's menus had me enter and save cable, attenuator, etc. data. But the file it created was empty. I had to manually enter data a second time with Excel.
There were a couple calibration tabs. The one intended for the configuration I purchased never activated GUI button to run calibration. I succeeded in using the system by calibrating with a different tab, because the settings I wanted (50 ohm) were available on both. Other settings (500 ohm) were not available. Equipment numbers not properly logged in results.

A whole lot of what is sold is cr*p. Vendors don't even test it operates as documented. This one said all their customers buy the hardware but write their own software.

Sure would be nice when doing something to a standard (e.g. for FCC compliance) to be able to buy a working system.
Alternative was an all-in-one box, which would have locked me down to custom hardware and software, no opportunity for self-support or feature addition. I did try to get such a system quoted, intending to have identical system as another division uses overseas, but an equipment rental company I contacted said they had several out of service because after consolidation of vendors they couldn't get the units repaired.

Standards, open source, full documentation and DIY seems to be the only way to have something last 10 to 20 years.

I mostly used GPIB in the past. Was once expensive, cheap enough today. Now I'm using USB and Ethernet instruments at work, but requires all sorts of proprietary drivers, never got all connected to the PC, have to use "I/O Expert" to kick them each morning or not recognized by my code (in Matlab).

@Hedges
I'm with you Hedges, some of the stuff out there is some real crap. I love to use open source whenever possible, so I can customize the code to my need. Much of my development work is web based, so even the licensed libraries are usually javascript and I have access to the code, just like an open source project, except I have to pay for the right to use it.

I can't tell you the number of times I've been using a closed source product or piece of software and have thought to myself, "I wish had the source code so I could fix this glitch or add this small feature that would make it perfect for my needs."

schmism said:

Freezer -

or
Freezer -

your going to need to specify the power requirements of the devices you want to run before you can answer your question.

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Haaaaa

Today was screw around with the system and see what it could do, took me a while to figure out that my inverter was not happy with anything more that 56 volts, and was just beeping and dying as soon I I plugged anything in. Changed the settings on the controller to not allow it to charge more than 13.9 per battery and put the protection at 11.5. I ran a 1500w heater for an hour, everything seemed happy, I have now been running my garage fridge/freezer for an hour, so looks like we are good here. Looks like it would run the heater no problem with sunshine, and probably for 3 hours in the night. Looks like the fridge uses about a constant 200w, it might make it through the night on batteries, I plugged in one freezer, not long enough for it to actually come on so who knows, I will have to just try it out and see what happens.

Might be useful to have a timer shutting inverter (or power to refrigeration) off at night.
If you're using lithium batteries not lead-acid, there shouldn't be a cycle life issue so not as important.
If inverter does shut off for low battery, does it automatically restart after sufficient recharge? (otherwise, refrigeration isn't backed up as desired.)
Which comes first, the inverter low battery shutdown or BMS shutdown? We like to have BMS be last line of defense.

Hedges said:

Might be useful to have a timer shutting inverter (or power to refrigeration) off at night.
If you're using lithium batteries not lead-acid, there shouldn't be a cycle life issue so not as important.
If inverter does shut off for low battery, does it automatically restart after sufficient recharge? (otherwise, refrigeration isn't backed up as desired.)
Which comes first, the inverter low battery shutdown or BMS shutdown? We like to have BMS be last line of defense.

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I have wireless temp monitors inside my fridges/freezers, and they lose temp pretty fast when turned off. You guys have fridges/freezers that hold things at a solid temp respectable temp all night with no power? Are you in sub zero climates or what? Maybe I keep my house too warm, or maybe kids are sneaking stuff out of them all night when I'm not looking.

I hear some well insulated chest freezers are better in that regard.

I haven't set up the monitoring to test the theory yet.
Ice does phase-change at 32F, but that means ice cream melts and other things get mushy.
The cold from the freezer could keep refrigerator cool, depending on air circulation. I'm presently dealing with a top freezer that doesn't have fridge as cold as I want (and it used to) when operating full blast.

The goal of my planned monitoring project is to see what temperature ranges my freezer operates in, then design a brine solution that starts warming a bit above coldest freezer temperature. Record the temperature range is goes through as concentration changes during melting, and see if it can work as night time cold storage for this application. (First I had to debug the issue of current sensor jamming the thermocouple circuits.)


Same setup will serve to evaluate secondary water heat exchanger for refrigerant of A/C system.

Yeah, my inverter does not have low battery protection until well below what my batts could tolerate. So that is an issue for sure .

Hauls Assington said:

Yeah, my inverter does not have low battery protection until well below what my batts could tolerate. So that is an issue for sure .

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I haven't even looked at the specs on your batteries so I don't know what you're supposed to expect. If you ran 1500W for an hour solid I expect at least one freezer to make it through the night and probably two. They probably aren't using 200W steady, they're using it until the stuff is frozen and then turning on and off with the majority of the time being turned off (maybe you'll have more runtime than I'm used to because higher temps at your location though).

I'm surprised your 1500W reliable WZRELB is complaining about 56V, I thought we ran ours up that high all the time (the 3000W). I did have issues with their 12V model voltage handling previously not going nearly high enough. This inverter will typically turn back on when the sun comes out and voltage goes back up in my experience. If your battery internal BMS' shut down though, that won't necessarily be the order of operation on your system?

Ideally, check out Victron smartshunt (or similar shunt that can track state of charge) so that you can track better how much power your batteries are really providing? BMV-712 model also has a relay to drive a disconnect based on tracked state of charge (an improved LVD function on some systems) and doesn't cost much more. I bought some L16 batteries 7 years ago that didn't really hold up for very long, and I wish I had the equipment to measure their capacity better now so I could have said something when I bought them.

One of my systems has the exact same problem with needing a low voltage disconnect still... The Victron shunt tells me I need to go charge the batteries if they get low and there's always somebody at my house to push a button on a generator, etc. But eventually I plan to use logic in the MPPT to drive a relay and cut DC power to the inverter as a low voltage disconnect, it seems like most good MPPTs have that option, even less expensive ones. You don't need to buy anything other than the relay and wiring I think for a rough LVD function, although I haven't used your MPPT before.

EDIT: My WZRELB 48V 3000W is currently running at 57.39V.

Nice work so far.

So since nobody actually explained it, the thing about the 'circuit breakers' is, especially on the battery side: The DC volts rating is not so much about keeping you from getting electrocuted when you touch the plastic case, but more about being able to 'extinguish the arc' that will happen when it opens/trips at or over its max current rating. The batteries if you think about it are more powerful than most welders.. even into a dead short they'll be doing over 40v, and until the BMS's melt or shutdown, the 4 of them will be pushing way over 1000amps if it's a dead short scenario. The kind of arc you can get going with 40v and 1000+amps can reach pretty far. If the contacts don't get far enough apart from each other the arc might just keep going and do some real exciting welding inside your plastic case, meanwhile everything downstream is still making 1000a+ worth of fireworks too.

Distance isn't the only thing about extinguishing the arc, i just think welding is the simplest analogy. So it's highly preferable to have a breaker/disconnect thing that can actually shut down an arc with that much power behind it, and that's why a high DC volts rating is important. Some also have a rating for max interrupt current. "Interrupting Capacity (IC) is the maximum fault current that can be interrupted by a circuit breaker without failure of the circuit breaker."

Ok finally back, I now have both freezers plugged in and running on solar, it seems to take between 180-220w constantly to run both. The question is, will the batteries make it through the night? And what happens if they dont. I have 4800 wh worth of batteries, so in theory it should make it no problem,

My system cut off at 8:00 AM the other day. Low-battery disconnect at 30% SoC, shortly before enough sun hit the panels.
To actually make it through one night, I need to turn off yard lights and an old tube amp.

Problem related to one breaker between grid and Sunny Islands tripping, must have been during full sun the day before. And older aged thermal/magnetic Schneider Multi-9 63A breaker. I want to replace those with magnetic-hydraulic, which shouldn't be affected by heat or need to be run at no more than 80% of rating. (I think current imbalance between parallel circuits contributes, but I've seen these things trip well below their rating.

My solar/battery/load math is a little fuzzy. Maybe someone can set me straight.

I have 48v-100ah battery

My freezers use 200w continuous.

How long in theory will the battery run the freezers?

Is my battery 4800wh?

If so would that be 4800/200 for a 24 hr run time?

Or am I way off here?

Vigo said:

Nice work so far.

So since nobody actually explained it, the thing about the 'circuit breakers' is, especially on the battery side: The DC volts rating is not so much about keeping you from getting electrocuted when you touch the plastic case, but more about being able to 'extinguish the arc' that will happen when it opens/trips at or over its max current rating. The batteries if you think about it are more powerful than most welders.. even into a dead short they'll be doing over 40v, and until the BMS's melt or shutdown, the 4 of them will be pushing way over 1000amps if it's a dead short scenario. The kind of arc you can get going with 40v and 1000+amps can reach pretty far. If the contacts don't get far enough apart from each other the arc might just keep going and do some real exciting welding inside your plastic case, meanwhile everything downstream is still making 1000a+ worth of fireworks too.

Distance isn't the only thing about extinguishing the arc, i just think welding is the simplest analogy. So it's highly preferable to have a breaker/disconnect thing that can actually shut down an arc with that much power behind it, and that's why a high DC volts rating is important. Some also have a rating for max interrupt current. "Interrupting Capacity (IC) is the maximum fault current that can be interrupted by a circuit breaker without failure of the circuit breaker."

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Ok, this makes total sense to me, would you mind, posting a link to the exact device you suggest I use? I will order it and install it in place of what I have.

That demand would cycle your batteries 100% each day. Not ideal.

But 12 hours, until sunup, is more reasonable.
With lead-acid, may get 2 to 4 years cycle life. Lithium, we hope 10 to 15 years (and they should tolerate 80% DoD with long life.)

Some freezers may be 200W continuous. My old one likely more. Some models a fraction of that.

Hauls Assington said:

My solar/battery/load math is a little fuzzy. Maybe someone can set me straight.

I have 48v-100ah battery

My freezers use 200w continuous.

How long in theory will the battery run the freezers?

Is my battery 4800wh?

If so would that be 4800/200 for a 24 hr run time?

Or am I way off here?

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That is how it works, your battery has 4800wh of capacity. You have to take conversion efficiencies into account though, your inverter loses some of that 4800wh when it converts from DC to AC. How much varies by the inverter and load it's driving, cable thickness and distance, etc..

Hauls Assington said:

Ok, this makes total sense to me, would you mind, posting a link to the exact device you suggest I use? I will order it and install it in place of what I have.

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Depending on where you're using it, ampacity of wire, etc...

Here are a couple breakers good for between a battery and an inverter. 50k AIC covers short-circuit current of most lithium battery banks.


Fuses like Class T or Ferraz Shawmut "amp trap" also have suitable AIC rating.

If you have a lithium battery, should use a resistor precharge before closing breaker or connecting power through the fuse, otherwise burns contacts, blows fuse, may stress BMS.