diy solar

diy solar

Has this been discussed somewhere? Are there inverters that automatically start up when connected to 12V?

Timselectric:

I assume the exception to the "don't put batteries with BMS in series" rule would be batteries that can communicate with each other, from one BMS to the other, right? If they are made for that, basically. I have seen that somewhere, just a simple cable connecting the two BMS so they can "talk" to each other. Can't remember where I saw it though.
Usually, they don't actually communicate with each other. They just connect together and pass all information to the inverter.
 
Ok, thanks again!

So just to clarify: Putting two 24V batteries that each have their own BMS in parallel would be ok?

EDIT: If their spec sheet states that is fine?

Or would that still not be a good idea?

Surely parallel must be ok I am thinking? How else is anyone building a large battery bank - or is a unified, single BMS which takes care of every single cell in all batteries in a centralized way really required when building a large battery bank?

For example, putting say two 24V batteries in series if I can't find a battery that has quite the capacity that I need - would that be ok or not?
 
"For example, putting say two 24V batteries in series if I can't find a battery that has quite the capacity that I need - would that be ok or not?"

I just noticed I wrote this wrong, I obviously meant in parallel here. But it sounds like you guessed that already.
 
Probably better to do that with identical capacity as well as brand and thus BMS, correct?

And better not mix batteries of much differing age either I'm guessing?
 
Probably better to do that with identical capacity as well as brand and thus BMS, correct?

And better not mix batteries of much differing age either I'm guessing?
Not as important with LiFePo4 batteries.
As long as they are good quality and not abused.
 
I've run a chest fridge for years. It is microprocessor based to control hot starts and preventing the battery from being killed from discharge. It will run for 5 minutes and then check to see if it is still over 13.3V. If not it shuts off. Battery basically is only used for starting surge. System only runs in the day, uses a MSW inverter with a small relay across the switch.
 
EfficientPV:

Thanks for sharing - that sounds very much like a setup that would suit really well for a second location that I am considering setting something like this up for:

Only run the compressor of a single chest fridge while the sun actually shines, battery only for compressor startup spike, bring temperature as close to zero degrees celsius as possible during sunshine hours, stop compressor at a cutoff voltage of the battery that will mean long battery life, accept the fridge inside warming up until the sun rises again.

May I ask:

1. What size is your chest fridge? Is it a converted chest freezer, I assume?

2. How many sunshine hours per day you get in your winter months where you live? What is your climate?

3. What are the specs of your solar panels that you are using for this setup? As in, combined rated power of your panels?

4. And finally: How warm does it get inside your chest fridge on the worst days?

This would be really useful to know for me.

I guess in principle one could do the same with a chest freezer... hm.
 
7CF chest freezer
Only use the camp from June to Oct in northeast
# of panels not applicable as more than 70% of them are shaded at any one time, under 800WH a day.
I run it down to 33F, in the morning it is 39F. New freezers are highly stratified, use a computer fan to circulate air. Very bottom actually freezes.
As I live there for 5 months food has to stay good. I runs the same even on rainy days.
 
Thanks, very useful information!

Do you actually use up those 800Wh / day, or is that just the number that you know your panels *can* generate in a day?

Can I ask what size inverter you are using?

Also, do you leave the inverter running 24/7, or do you do anything to avoid it standby consumption?
 
Those measurements were made from a power meter on the 12V going into the inverter. I used a 200A shunt to handle the 120A surge with a $10 50A power meter in parallel. That calibrated to a 8.6 power multiplier. Usage can change that. Don't try putting in new groceries at 4pm or it won't have time to cool them.

I use only an old Harbor Freight 2,000/4,000W MSW inverter with the fans removed to lower running current. A relay is on the power switch, it only runs when the fridge turns on. The fridge only runs in daylight hours. Cold is stored in a large mass of liquids for overnight.
 
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