Refrigerator Issues - Dropping 2 Volts

[NomadicMovement]

Hey all - First time poster but long time reader. You all have been a big help in my conversion and i'm hoping you can help me with this really interesting issue. I'll try to explain this as best as I can but I am not a professional by any means.

I have a 45 quart Whynter fridge. When the compressor turns on, the volt meter LED display on the fridge will show a drop in voltage by 2-2.5 volts and will sometimes drop below the 10v threshold (set on the fridge) and turn the entire system off. But when I disconnect the fridge, my charge controller is showing me a >75% charge left on my battery.

I have checked all the electrical connections for the fridge and they all appear to be solid. The fridge is connected to my fuse box using 12 AWG. My battery is connected to my solar charge controller using a 10 AWG.

Any ideas on how I can pinpoint the issue?!

Thanks all!

[brokedown]

How large is your battery? Voltage drop under load is normal, it's hard to judge how much it should be without knowing the capacity of your supply. For reference, my freezer drops my voltage about 1.0-1.2v in full sun.

[family wagon]

The model FM-45G web site says its 12v draw is 4.5 amps (I'm not sure whether that's exactly the model you have). That's not extreme; your wire gauge is probably reasonable unless it's a very long run.

As for how to pinpoint: with a volt meter. Measure voltage across every segment of the circuit. Positive battery post to the wire terminal, then wire terminal to the fuse block, fuse block to the appliance, appliance back to negative wire terminal, negative terminal to battery post. Look for any of these to show 0.1 volts or more. Once you know where the biggest part of your voltage drop lies we can offer ideas on how to reduce it.

Do you have a dedicated negative/ground return for the unit? If it's grounded to the vehicle body then don't forget to check the connection from the vehicle body back to the battery negative. That link is often overlooked but is just as critical as any of the connections on the positive side.

brokedown makes a good point... before going to the pains I described, measure the post-to-post voltage right at the battery. If it matches what the appliance shows then you probably just need more battery.

[Jolly Roger]

Just some thoughts?
Is your charge controller sized enough to handle the fridge?
Maybe look at adding a soft start capacitor to the fridge compressor to help handle the extra surge on start up?

[NomadicMovement]

Originally Posted by family wagon

The model FM-45G web site says its 12v draw is 4.5 amps (I'm not sure whether that's exactly the model you have). That's not extreme; your wire gauge is probably reasonable unless it's a very long run.

As for how to pinpoint: with a volt meter. Measure voltage across every segment of the circuit. Positive battery post to the wire terminal, then wire terminal to the fuse block, fuse block to the appliance, appliance back to negative wire terminal, negative terminal to battery post. Look for any of these to show 0.1 volts or more. Once you know where the biggest part of your voltage drop lies we can offer ideas on how to reduce it.

Do you have a dedicated negative/ground return for the unit? If it's grounded to the vehicle body then don't forget to check the connection from the vehicle body back to the battery negative. That link is often overlooked but is just as critical as any of the connections on the positive side.

brokedown makes a good point... before going to the pains I described, measure the post-to-post voltage right at the battery. If it matches what the appliance shows then you probably just need more battery.

Just got a Multimeter and did some tests. (250 amp hour battery)
Idle Battery - 13.6v
Let refrigerator run for 5 minutes and took readings:
Battery 12.9v
Battery connection at solar charge controller - 12.5v
Load connection at solar charge controller - 12.1v
Refrigerator connection at fuse box - 12v
Refrigerator LED reading - 11.6v

Does this mean the connections at my charge controller are bad?

Thanks for the help!

[family wagon]

Apologies for the electrical engineering terminology and assumptions.. I'll back up a little bit. With a volt meter you can measure voltage from anywhere to anywhere; you're not limited to holding the black lead on the negative point in the circuit and only probing around with the red one. When I wrote "across" what I had in mind was to put one of the leads at one side of the "across" section and the other lead at the other side of the section being measured. More on that in a moment.

Still, your numbers are useful. Seeing 12.9 volts on the battery and 12.0 at the refrigerator terminal on the fuse block is significant; ordinarily the fuse block would be connected such that there should be little difference in voltage between the battery and the fuses. The 0.9 volt difference here is most of what's missing at the refrigerator so let's dig into that first.

Maybe you could provide us a schematic sketch of the circuit. That'll help us avoid making assumptions and/or asking for measurements that don't make sense.

If you could also report the voltage measured with one meter lead at the battery's negative terminal and the other lead at the refrigerator's negative, as well as the voltage with one lead at the battery's positive terminal and the other lead at the fuse block input, that'll help focus the search.

[bubb, the real one]

1amp AC equals about 10 amp D.C.
1 think your device pulls 4.5amp AC not D.C., since 4.5amp D.C. Would equal 0.45 amp ac and that sounds too weak to make cold .
And if I'm right you are pulling 45 amps on a 250ah battery, it is best to not pull over 10% of a batteries amps,
And you have the LRA issue when a motor first starts it may pull 2 to 4 times more power for a few seconds, recalculate the 10ga wire load on 45 amps

edit to add,
I meant to say the 12ga wire sounds too small, especially if it is over 3ft long, DC does not travel distance well at all,

[NomadicMovement]

Originally Posted by family wagon

Apologies for the electrical engineering terminology and assumptions.. I'll back up a little bit. With a volt meter you can measure voltage from anywhere to anywhere; you're not limited to holding the black lead on the negative point in the circuit and only probing around with the red one. When I wrote "across" what I had in mind was to put one of the leads at one side of the "across" section and the other lead at the other side of the section being measured. More on that in a moment.

Still, your numbers are useful. Seeing 12.9 volts on the battery and 12.0 at the refrigerator terminal on the fuse block is significant; ordinarily the fuse block would be connected such that there should be little difference in voltage between the battery and the fuses. The 0.9 volt difference here is most of what's missing at the refrigerator so let's dig into that first.

Maybe you could provide us a schematic sketch of the circuit. That'll help us avoid making assumptions and/or asking for measurements that don't make sense.

If you could also report the voltage measured with one meter lead at the battery's negative terminal and the other lead at the refrigerator's negative, as well as the voltage with one lead at the battery's positive terminal and the other lead at the fuse block input, that'll help focus the search.

.65 from negative terminal on battery to refrigerators negative

.01 from positive terminal on battery to fuse box input.


Here's a quick sketch of my electrical system
http://imgur.com/a/KrmMk

[NomadicMovement]

Originally Posted by bubb, the real one

1amp AC equals about 10 amp D.C.
1 think your device pulls 4.5amp AC not D.C., since 4.5amp D.C. Would equal 0.45 amp ac and that sounds too weak to make cold .
And if I'm right you are pulling 45 amps on a 250ah battery, it is best to not pull over 10% of a batteries amps,
And you have the LRA issue when a motor first starts it may pull 2 to 4 times more power for a few seconds, recalculate the 10ga wire load on 45 amps

edit to add,
I meant to say the 12ga wire sounds too small, especially if it is over 3ft long, DC does not travel distance well at all,

4.5 amps DC. See specs below

[warewolff]

I may be misunderstanding but can you share a little more info? You should be having no issues pulling 65w with that setup. At 13.6 your battery is actively being charged. It should level out at 12.6-12.7 after an hour or so of sitting with no charge. 12.9 is still coming down from a full charge to the resting state. I don't understand why your battery is reading 13.6, indicating a state of charge, while the "load" side of your charge controller is reading 12.1.

Is it possible your batteries are not fully charged? Just because they read 13.6 volts for awhile doesn't mean they're topped off. Your charge controller should be pumping anywhere between 13.5 and 14.5 volts depending on the state of charge -- 14.5v or more being a "bulk" charge and ~13.5v on "absorb" or "float". My batteries need a few hours in absorb, after bulk charging, before they are topped off. What I'm saying is it's easy to think your battery is fully charged when it's really not.

Furthermore, if it's daytime and your charge controller's "load" side is reading 12.1 ... you've got a problem. There's no way you're charging your batteries with 12.1 volts, as I previously explained. That's either bad wiring or a malfunction somewhere. To put it in perspective, unless you're running everything in parallel on your roof, the voltage multiplies. That's why MPPT controllers are so great.
They chop it all up and spit out what your batteries need.
Wired in series, each of my charge controllers are receiving over 120v on the "load" side and, as previously stated, between 13v and 14.5v (okay, 15.5v if I'm equalizing) on the battery side.

Even when the batteries are fully topped off your charge controller should still be putting out over 13 volts at a few amps. What kind of charge controller are you using? What are you using in regards to solar panels? All of this matters. It's possibly a combination of it all. Are you sure your solar setup is not merely trickle charging your depleted batteries?

Also, depending on the voltage you have running through those wires, 10 awg is way too small between your charge controller and your batteries.

Reply back and we'll see if we can get this sorted out for you...

[family wagon]

Thanks for the schematic. What's the make and model of the charge controller? I'm unfamiliar with the topology where the charge controller has a pass-through function for the dc loads -- I had expected those to be wired directly to the battery. I'd like to read up on the model you have. It seems not to be passing power from battery to loads as well as one would hope for.

[NomadicMovement]

My apologies, its a 20A charge controller. It's Komaes PWM Controller

Here's the link to the package I purchased:

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

[bubb, the real one]

Thanks for the cooler specs,
how long are you wire runs:
battery to inverter,
inverter to fuse,
fuse to fridge,
are you able to post pictures of the battery terminals, inverter terminal, fuse box connectors,
Just like the other posters I wonder if it is voltage drop from some combination of wire size, wire length, connection quality,

[NomadicMovement]

I tried to reply to this but I'm not sure why it didn't post...

Its a Komaes 20 amp PWM controller

[NomadicMovement]

It's a short bus so the runs aren't too long

Battery to inverter is 3'
Battery to charge controller is 5'
charge controller to fuse box is 20'
Fuse to fridge is 10'

I've triple checked all connections and they are solid. I'm starting to think its the charge controller... not sure if that would make sense for a 2 volt drop though...

[family wagon]

I'm leaning toward charge controller fault too. Unfortunately it looks not well supported: I searched a bit online and found plenty of offers to sell the unit, but didn't quickly find any place to download any kind of user or installation manual.

It occurred to me this controller might be using low-side switching, meaning that it switches the negative/ground side rather than the positive side as people are accustomed to do. The electronic circuit inside can be built a little simpler and less expensive with low-side switching. However, strange behavior could result if the solar panel, battery, and load grounds are not kept isolated from one another. If those three grounds aren't isolated from one another already, try isolating them. In other words, don't use the vehicle body/chassis as the ground return for the panels or the refrigerator. Use a separate wire run all the way back to the controller terminal.

The spec charts I saw on amazon, ebay, etc said this unit should have less than 0.15 v drop from battery to load. Measure the voltage between battery+ and load+, and from battery- to load-, to confirm the drop there really is less than 0.15 v as advertised. If it's not, disconnect both battery and load from the controller, wire them together directly, and check the voltage at the load.

[bubb, the real one]

Can we do some testing?
Cab you remove the charge controller and just have the fuse box connected directly to the battery, then do a measurement.
Try the same thing with he fuse box and controller both gone.