Want to build system to run fridge

[rjmetals]

24V system. Bulk charging reaches a high of 28.8V per MT50 readings before charge controller backs it down.
Panels are not aimed directly at the sun. They are mounted on a flat patio roof. I hadn't considered angle to the sun. Shocked that the angle would make that much difference out here in the desert Southwest.

Just wanted to say thanks to Hedges and all the rest who helped me set up my system. It's been completely assembled for well over a year now with no problems whatsoever. I run it for a week or so every 1-1.5 months to keep batteries up and it just performs the tasks it was built for; emergency backup for full sized fridge/freezer, TV and lights. Haven't had a real blackout yet...knock on wood. Thanks again! RJ

 

[rjmetals]

3 x 195W (STC) = 585W (STC)
350W/585W = 60%

I think PTC rating of panels (output under full sun but normal operating temperature) is often 85% or so of STC.
What you don't know is if you have "one full sun", or somewhat attenuated by something in the atmosphere.
The days are getting a bit shorter, so just path length through air is longer.
So the output could be normal, due to sun/atmospheric conditions. Or it could be a bit less than expected.

Are the panels aimed directly at the sun?
Is battery voltage such that full bulk charging is expected?

 

[rjmetals]

Thanks to all.

 

[rjmetals]

3 x 195W (STC) = 585W (STC)
350W/585W = 60%

I think PTC rating of panels (output under full sun but normal operating temperature) is often 85% or so of STC.
What you don't know is if you have "one full sun", or somewhat attenuated by something in the atmosphere.
The days are getting a bit shorter, so just path length through air is longer.
So the output could be normal, due to sun/atmospheric conditions. Or it could be a bit less than expected.

Are the panels aimed directly at the sun?
Is battery voltage such that full bulk charging is expected?

Just wanted to say thanks to Hedges and all the rest who helped me set up my system. It's been completely assembled for well over a year now with no problems whatsoever. I run it for a week or so every 1-1.5 months to keep batteries up and it just performs the tasks it was built for; emergency backup for full sized fridge/freezer, TV and lights. Haven't had a real blackout yet...knock on wood. Thanks again! RJ

 

[pollenface]

I currently run a 265L fridge/freezer from 980ah of agm on a 2000w psw inverter.

I have about 5kwh of usable battery power available but never use more than 1.5kwh/24hrs.

The fridge is outside in the elements, it would use less in summer if it were inside the house and extra insulation added.

Adding extra insulation to the exterior and filling the empty spaces on the interior helps with efficiency.

 

[Sticky1]

To measure start-up accurately, the best way is probably to use an ammeter. One of the clamp-around meters should do the trick.

An ammeter with a hold function. Volts x amps = watts

 

[Sticky1]

I currently run a 265L fridge/freezer from 980ah of agm on a 2000w psw inverter.

I have about 5kwh of usable battery power available but never use more than 1.5kwh/24hrs.

The fridge is outside in the elements, it would use less in summer if it were inside the house and extra insulation added.

Adding extra insulation to the exterior and filling the empty spaces on the interior helps with efficiency.

Don’t forget… over time the compressor, fan and electronics will degrade and pull more current. Overside a little

 

[Sticky1]

Perfect so long as inverter is 100% efficient and voltage after IR drop in cables never goes below 24V.

Fuses are supposed to be small enough to blow before cables overheat.
Fuses should be large enough that they never blow simply due to expected load (only if there is a short circuit or malfunction in inverter).

To avoid nuisance trips (of breakers) or blowing (of fuses), they are sized 25% higher than maximum continuous load.
They will tolerate brief higher surges (so long as not of the "fast blow" variety.)

What is the inverter efficiency? It may say "peak efficiency 95%", but at 100% load will be lower. I'll assume 90%.

What is the lowest battery voltage, under load? I'll assume 20V for a 24V battery.
How much voltage drop in cable at max current? (I'll include that in the 20V)

2000W/20V = 100A
100A x 1.25 = 125A

So 125A would be a common recommendation for this case.

I have determined that when driving a heavy AC load with an inverter, rather than steady 100A DC from battery, the current follows AC sine wave going higher and then dropping near zero. Same power is delivered to inverter but heating of wire and fuse (which goes as square of the current) is 12% higher.

125A x 1.12 = 140A

Although 2 awg in a cable or conduit would get too hot, individual conductors with free air to cool them are OK.

Wire Size Chart for Conductors in Free Air

Wire Size Chart: Allowable Ampacities of Conductors in Free Air - 30C

wiresizecalculator.net

So I would recommend 150A fuse.

You can get away with 100A if you don't draw 2000W except briefly (e.g. microwave for a couple minutes.)
But better to design it so fuse just provides protection against overloads, never leaves you in the dark otherwise.

If you can use 2/0 rather than 2 awg, that is better for reduced voltage drop, and keeps them cool.
I used 2/0 for 6000W at 48V (equivalent current to 1500W at 12V)

Other thing to consider is type of fuse. You haven't mentioned type of battery in this thread. Lead-acid? or Lithium?
If a cable short-circuits, lead-acid batteries can typically dump 3000 to 5000A. Lithium batteries have lower internal resistance, can dump 20,000A (I think.)
Fuses have an AIC (amps interrupting capability) rating. Class T is rated 20kA AIC up to 125V. Various other types have ratings such as 2kA at 48V & 5kA at 12V.
Depending on your battery, select a fuse that can handle its short-circuit current at 24V.

Here's an ANL fuse rated 5000 AIC at 32V

ANL Fuse - 150 Amp - Blue Sea Systems

Use with ANL Fuse Blocks for many applications with 35-750 Amp loads

www.bluesea.com

MRBF 5000 AIC at 32V

MRBF Terminal Fuse - 150A - Blue Sea Systems

Space-saving ignition protected fuse for 30 to 300 Amp loads. Must use with Terminal Fuse Block.

www.bluesea.com

Class T 20,000 AIC at 125V

Fuse A3T / Class T 150 Amp - Blue Sea Systems

Use with Class T Fuse Blocks for circuit protection of devices including inverters. high interrupt capacity for large battery banks including Lithium-ion and TPPL batteries.

www.bluesea.com

Why not use this style with disconnect or whatever amperage you need

187-Series Circuit Breaker - Surface Mount 100A - Blue Sea Systems

Thermal circuit breakers provide heavy duty circuit protection for 25 to 200 Amp loads when switching and circuit protection are both required.

www.bluesea.com