NovaKool gremlins - input DC voltage low

[KyleR]

Hi all! Our NovaKool (RFU8000) on our 2002 396 has been working intermittent recently when supplied only from DC power. On AC power it works great with no issues.

I pulled the unit out and pulled all connections, cleaned them and verified no corrosion issues at the fridge. The only issue I found was a low voltage of 11.7 - 11.8VDC at the input to the electrical box where AC and DC come together. House voltage was 12.4VDC at the time. So at this point I am thinking a ground/corrosion issues on the feed.

I then called NovaKool - great customer service BTW - just to make sure there was nothing else I should be looking at while I had it removed (that thing is heavy!). He said his concern was the low voltage and said the unit has a low-voltage protection cutout at 11.4VDC. Other than that he said the compressor is a DC unit and since it is working fine on AC then the converter and "black box" seem to be working okay.

So I have been chasing down wiring now and per the DC schematic the red wire runs straight from the DC panel to the fridge. But, I am not sure where the black wire ties in. I am guessing it goes to a bus bar somewhere but I am not sure where.

I found a common DC grounding bar in the engineroom on centerline all the way forward on the bulkhead and removed/cleaned/reinstalled each of those connections (10 total) but no change.

Are there other DC grounding bars that I haven't found that I can go after? How easy is it to pull open the DC panel on a 396 (i.e. are wires long enough)? Any other words of wisdom?

Electrical gremlins!!

Thanks in advance and sorry for the long post - just trying to give as much info as possible.

[Midnightsun]

Try measuring voltage from a good ground and the dc input of the fridge to see if your problem lies in the 12v positive side. Do the same for the negative side. At least this way you know where the problem lies. Hate those electrical gremlins.

[g36]

I would look behind your ac/dc electrical panel in the boat your negative bus should be there. I suspect you may have been seeing the common bus for bonding in the engine room. The true dc bus bar will have many many more than 10 connections.

[mjk1040]

Do you have 12.4 volts at the panel fridge breaker switch on both sides?

[bud37]

Have to say.....12.4 vdc seems a bit low to me......was your battery charger on at the time....what is the vdc at the battery terminals ?

[KyleR]

Thanks for all the suggestions. We should make it to Green Cove Springs tomorrow so I'll be pulling the fridge (again) and taking the measurements as suggested.

To answer some of the questions:
- thanks for the feedback on the DC bus in the DC panel. The bus in the engineroom is definitely a DC bus. It has a big black DC line running to it from the battery and all the other connections are black or brown wires. Also there is another DC bus under the helm for all those connections so I know there are multiple DC busses. I just don't know where they all are.
- There is a bonding bus adjacent to the DC bus in the engineroom and it has only green wires running to it that run from the through-hulls and whatnot. And there are multiple bonding busses throughout the engineroom that are definitely distinct from the DC busses.
- I have not measured voltage on the DC panel switch yet. I was hoping someone else had opened their panel and might give me an idea of what to expect. I know some panels don't give you a lot wire to pull the panel out - plus those wires sometimes get hard over the years and don't like to be flexed! I can just see me opeing the panel and breaking multiple connections due to stiff wires!
- 12.4VDC was with no AC or generator (i.e. chargers off) and on the battery for a few hours. Typically after I shut off the generator or shore power, DC voltage stabilizes around 12.9 then slowly depletes due to usage. On AC/generator I think it normally is around 13.6 or so - I'd have to check my records.

Thanks again for the comments! Hope to dig into this tomorrow or Monday. I'll keep this thread posted. But if there are any more suggestions please keep them coming!

[KyleR]

Update: pulled the DC panel open and started taking voltage readings starting at the house battery terminals and then every connection point I could find from there to the DC panel.

I found another DC distribution block on the engineroom aft bulkhead just below the chargers. There was also another DC distribution block behind the DC panel. I had battery terminal voltage at each one of these (using a long jumper from the positive battery terminal to my meter).

I also took readings at the breaker (both sides) in the panel and had full battery terminal voltage there as well. I saw no voltage drop on any connection - and I checked every possibility I could find. I even ran long jumpers from the battery to my meter when checking connections, as well as taking them locally in the panel. No smoking gun.

And once the wires leave the DC panel they go into massive bundles and then into plastic corrugated sleeves and disappear in the outboards of the hull!

The only thing I didn't do the other day was actually disconnect the DC input wires to the fridge and take readings directly on the wires.
I just took a reading on the block where the wires were inserted. So, I'm going to pull the refrigerator again and try that and see what I can see.

That's all for now. Thanks again for the suggestions!

[km1125]

When you pull the wires at the fridge and measure them, make sure you put some kind of load on it when you're taking the measurement.

That really should also apply when you're doing any kind of measurements for "voltage drop", because if there is no load, then there's no voltage drop. If you weren't putting loads on when you took all those measurements then you were really just checking continuity rather than for actual voltage drop.

You can use just about anything to create the load, but if you're troubleshooting something like this fridge issue, then you should use a similar load that the fridge would cause (or larger). Frequently I'll use old incandescent automotive bulbs as a load. An old brake light can be a couple amps and an old headlamp can be 5 or 10 amps. One of those electric "automotive heaters" can give you a good 10 or 20 amps and you can buy those things cheap (sometimes almost free) at yardsales.

And, as stated earlier, whenever you are checking for voltage drop then check the positive side separate from the negative side. When checking the positive side, then connect the meter negative directly to the source (battery) with a long decent-sized wire.

[KyleR]

Thanks km1125 for the input! I had the refrigerator running the entire time on DC (chargers off) and the compressor was running so I had a load on the system. Plus the other DC loads like lights and electronics were on, however the fridge is by far the largest load. But I hadn't thought about the fact that once I disconnected the wires at the fridge the load would be lost - good point!! Kinda obvious once pointed out!!

And yes, I ran a long jumper from the negative pole on the battery when measuring the voltages on each (positive) side of the switch.

Thanks again!!

[km1125]

Source of the post<snip>
And yes, I ran a long jumper from the negative pole on the battery when measuring the voltages on each (positive) side of the switch.

Also, just to clarify my earlier note (and for anyone else who might be referencing this thread)...

When looking for "voltage drop" issues it's preferable that you have the negative of the meter always hooked directly to the source (battery) and you check battery voltage at the battery. Let's say it's exactly 12.6 VDC. This establishes a constant reference to the battery negative. If you keep moving the meter negative connection, then you lose your reference and it makes comparing readings harder.

If you've done that, then if you measure at the helm or some other place on the boat and you get 12.1 VDC that'd be 0.5 Volts of voltage drop (might seem quite obvious), but then you measure the negative side at that same spot and you actually measure 0.5 V that means there's actually only 11.6 VDC at the device... loosing 0.5 on the positive side and another 0.5 on the negative side.

You could say I get 'triggered' when I hear somebody say "I saw no voltage drop on any connection" when they're looking for a voltage problem. You MUST be reading some kind of voltage drop or you're not doing something right. That's just how electricity works. The question is if you're seeing the RIGHT amount of voltage drop. In the OP's situation, he might be seeing a total of 1.0 Volts drop... from the battery at 12.4VDC and the device is set to cut off at 11.4VDC. HALF of that 1.0 Volts of drop is probably "normal" (we could actually calculate what it should be if we knew all the details, but "half" is a decent swag). So he needs to be looking at only about 0.25 Volts as a "culprit", as half of the unknown could be in the negative side and half could be on the positive side. Every tenth really starts to count.

AND, he might not have a problem at all, as many circuits are designed for a 10% drop. In this case, that would mean 1.2 Volts.