Voltage Drop Dometic CFX 75DZW

[jnack]

Full Disclaimer: 12v electric is not my area of expertise.

I am able to measure the voltage at the fridge via the wifi app (I'm assuming this is accurate).

Condition 1) When the fridge is off, but power is on to the plug the voltage at distribution block and at the end of the Dometic plug is identical (read via voltmeter).

Condition 2) When the fridge is connected but compressor off: voltage at fridge (read via Dometic Wifi app) 0.4V less than at distribution block.

Condition 3) When the fridge is connected, compressor on: voltage at fridge 0.6V less than at distribution block.
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I initially had 10AWG wire for both power and ground, total length about 28 ft wired to aux battery under the hood. I re-wired the fridge to the battery in truck bed which is now a total length of about 9 ft AWG due to shorter length and chassis ground. Ironically, the voltage drop was very similar to the initial much longer run of wire.

I had purchased 8AWG wire to use for this application, but since I was able to cut down on length by 2/3 I figured that 10AWG should be sufficient.

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I was thinking with the much shorter distance of the wire I shouldn't have as much voltage drop. I'm pretty disappointed with the difference of 0.6V. I have it set to low battery cut off of 10.1 V, which means the Dometic is seeing 10.1 but the battery is still at 10.7.

Am I not measuring the voltage drop correctly? Is it possible that this is a problem with the way the fridge voltmeter is working? I wish there was a way for me to use the same voltmeter to measure the power at the fridge, but can't see a way to do that without messing with the wiring/plugs.

 

[verdesard0g]

Wire has very little resistance, for a difference of length you have described there will not be much difference in voltage loss with the same current flow. Wire resistance us usually stated as ohms/thousand feet.

 

[luthj]

Poor or excessive connections can cause higher voltage drop. 10.1V is a totally depleted battery. Typically 10.5V is the Lower bound in capacity testing. Note that regularly discharging a battery to that level will have a significant impact on its lifespan.

if you would like to identify where specifically the voltage drop is occurring you can do this using a simple voltmeter. With the fridge running probe both sides of various connections or wires. the voltage drop will show up on your meter and you'll be able to narrow it down to either a section of wire specific connection etc.

 

[Alloy]

Start with using the same device to measure the voltage.

I've poked the probe of the voltmeter thru the insulation of the wire but there must be a way to access the connections in the fridge.

Use a clamp-on amp meter to measure the amperare and determine the fridge isn't drawing too much power.

It would help if we knew what the starting viltage is.

Is the battery old?

Battery terminals clean?

Connections crimped properly and heat shrink used?

Terminals clean (with Scotchbrite pad) and a tiny amount of silicone grease used?

 

[jnack]

Poor or excessive connections can cause higher voltage drop. 10.1V is a totally depleted battery. Typically 10.5V is the Lower bound in capacity testing. Note that regularly discharging a battery to that level will have a significant impact on its lifespan.

if you would like to identify where specifically the voltage drop is occurring you can do this using a simple voltmeter. With the fridge running probe both sides of various connections or wires. the voltage drop will show up on your meter and you'll be able to narrow it down to either a section of wire specific connection etc.

I understand how that works in theory, the challenge is that would involve stripping wires to get the voltmeter before and after a connection ie. this fridge is plugged into an ARB 12V outlet

 

[jnack]

Start with using the same device to measure the voltage.

I've poked the probe of the voltmeter thru the insulation of the wire but there must be a way to access the connections in the fridge.

Use a clamp-on amp meter to measure the amperare and determine the fridge isn't drawing too much power.

It would help if we knew what the starting viltage is.

Is the battery old?

Battery terminals clean?

Connections crimped properly and heat shrink used?

Terminals clean (with Scotchbrite pad) and a tiny amount of silicone grease used?

my concern is the insulation, as that would require stripping insulation. battery is new with clean terminals. all connetions crimped properly with heat shrink

 

[Alloy]

my concern is the insulation, as that would require stripping insulation. battery is new with clean terminals. all connetions crimped properly with heat shrink

The point of the probe is poked (don't drive it into your hand) into/through the insulation. If you want self sealing tape or sheat shrink will cover the hole.

 

[luthj]

Some connectors can be backprobed. If they have silicone seals around the wires, there are needle probes which slip between the seal and the wire without damaging anything.

 

[jonyjoe101]

Is the wire you are using pure copper? some wire sold is copper clad (speaker wire) . I use to buy the cheapest wire and notice voltage drop problems. I buy pure copper wire now.

Also are you using the oem 12 volt plug (cigarette adapter), those types of plugs aren't the best for getting max performance, they lose watts thorugh heat, you can feel them getting warm. I remove those plugs and use xt60 plugs on all my high amps devices, xt60 connecters is like pure wire, I never feel heat on them.

If you are using pure copper, I suspect the LED meter on the fridge is reading low.

 

[jnack]

Is the wire you are using pure copper? some wire sold is copper clad (speaker wire) . I use to buy the cheapest wire and notice voltage drop problems. I buy pure copper wire now.

Also are you using the oem 12 volt plug (cigarette adapter), those types of plugs aren't the best for getting max performance, they lose watts thorugh heat, you can feel them getting warm. I remove those plugs and use xt60 plugs on all my high amps devices, xt60 connecters is like pure wire, I never feel heat on them.

If you are using pure copper, I suspect the LED meter on the fridge is reading low.

the dometic 12v plug unscrews so i am using the 2 pin threaded connector. i wouldn't exactly consider the draw from the fridge to be "high amp" though. it's tinned copper wire, ancor brand -- stuff isn't cheap either.

 

[jnack]

So I contacted Dometic Customer Support and their engineers are saying that they are seeing voltage drops of 0.2-0.8v routinely. That seems pretty substantial to me. What are you guys seeing for voltage drop on these fridges?

 

[rayra]

chasing your tail again. Two different measuring devices = two different readings.
Using a multimeter, measure your voltage at the supplying battery terminals. Using the same measuring device at the other end of the wiring run at the plug / socket your fridge is plugging in to. What the Dometic is reporting doesn't matter.

 

[jnack]

To add,
Measure those voltages when fridge is running. In this scenario, measuring ’voltage drop’ must include a load on the circuit.
That likely requires minor creative method of connecting your meter at the fridge end of wiring whilst the fridge is connected also.
Its the only way to gain meaningful information.
Btw,
While at it. Measure voltage at each end of the circuit just before fridge motor switches on, and see how voltage drops once its motor is running.

appreciate it. while measuring voltage at the fridge end would it be sufficient to strip the wires right before the connector to the actual fridge? I feel as though it would be nearly impossible without potentially seriously damaging the fridge terminals to jam the prongs from the voltmeter in there somehow

 

[jnack]

Stripping is little destructive too...
Were I doing it, probably take fine 26AWG or there abouts wire and stick that into the ends of the fridge cord then plug the cord into the fridge inlet, trying to trap the fine wire between the male to female pins/socket connection.
Or put a few wraps of fine wire around the male pins of the inlet, then plug the cord onto the fridge.
Measure voltage on those fine wires what are now sticking out.
Failing either of those, would partially disassemble the fridge in order to access back side of the inlet.

ive already ordered a new cable which I plan to use as a spare in case something happened to the initial one so stripping the wire wouldn't be the worst thing. finding 26 AWG might be challenging -- i suppose if i tried that route wouldn't that small caliber wire cause increased resistance and hence falsely elevate the voltage drop?

 

[Dometic]

Are you using OEM wiring and plug to power your fridge? We've seen some crazy levels of voltage drop across some OEM power outlets. Our product manager has a FJ60, and the drop is so bad from an OEM dash-mounted outlet he can't power a CFX at all.

When you start running the cooler, you should expect some voltage drop. That said, the gauge wire, poor electrical connectors, and old wiring can greatly impact the level of drop when a load is applied.


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