NovaKool gremlins - input DC voltage low

[KyleR]

Thanks for taking the time to detail all this information - the effort certainly is appreciated! It's so difficult at times to express things adequately in a post so I definitely didn't mean to trigger anyone with my terminology.

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.

The main reason I see it as a problem is that for the last 5 months that we've owned the boat the refrigerator has worked without issues - even when battery voltages dropped to 12VDC or so. Now all the sudden the fridge cuts off when house voltage dips below 12.4VDC or so. Something has changed and I'm just trying to sort it all out.

Again - thanks to all for the suggestions and teachings!

[bud37]

You know it may just be the simple....the fridge power supply is faulty. I commend you for the testing though , nice job so far.....good luck.

[km1125]

Source of the post Thanks for taking the time to detail all this information - the effort certainly is appreciated! It's so difficult at times to express things adequately in a post so I definitely didn't mean to trigger anyone with my terminology.

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.

The main reason I see it as a problem is that for the last 5 months that we've owned the boat the refrigerator has worked without issues - even when battery voltages dropped to 12VDC or so. Now all the sudden the fridge cuts off when house voltage dips below 12.4VDC or so. Something has changed and I'm just trying to sort it all out.

Again - thanks to all for the suggestions and teachings!

Rethinking this and I'm also wondering how old the batteries are? Is it possible you're getting into an older battery and it's not holding the voltage up as long as it used to? (when we're talking about 0.1V making a difference!).

The other thing I wondered about is if perhaps some of your activities changed. In the voltage-cutoff circuits, there is usually some 'hysteresis' built into the circuit. It may cut off at 11.4VDC, but may not reactivate until the voltage rises above 11.8 or 12.0 volts, then it "resets", and will then run normally until (or if) the voltage drops back below 11.4. However, if the voltage never rises past that "reset" level, the fridge would not run on D.C.

Is it possible that some OTHER (seemingly unrelated) action on the boat might cause the voltage to drop below the threshold at the fridge (11.4VDC) long enough to trigger the cut-off circuit but when that load is removed the voltage goes up above 11.4 but not enough to reset the cut-off circuit? Perhaps some other temporary load like a vacu-flush cycling or using a winch or some other temporary heavy load? These would drop the voltage at the battery and even more at the distribution panel (due to voltage drop) which could cause the cutoff circuit in the fridge to be triggered and it wouldn't reset until the voltage rises to some set level.

What complicates this is that the other load would have to happen when the fridge compressor is running. This is because the fridge compressor is also causing some voltage drop in the line right to the fridge. This would make identifying the issue a little tricky, as you might say "we use the vacu-flush (for example) all the time, and the fridge just intermittantly stops running on D.C.". It could be that, just by coincidence, many times you use that vacu-flush (or whatever load) just happens to be when the fridge compressor isn't running so then the cut-off circuit doesn't get triggered. But other times it does because the compressor is running when that other load is activated.

[KyleR]

First of all - thank you for taking the time to respond with so much detail and thoroughness as I know that takes a lot of time! I am grateful!!

It's very interesting that you posted this! As I was laying awake last night trying to figure this out it dawned on me about some of the battery issues we had when we bought this boat. They originally had the house deep cycle batteries wired to the main engines and the 1000amp CCA batteries wired as the house batteries. Also,the chargers were improperly wired and the generator battery wasn't even connected to a charger! But that is a whole other thread! I have a feeling these batteries were not taken care of by the previous owners the way they should have been.

Plus, I also noticed this past week that when the battery voltage was lower and the potable water pump kicked on, often times the refrigerator compressor would cycle off. Sometimes it would restart sometimes it wouldn't which ties into the other point you made about other DC loads pulling voltage down momentarily causing the cutout to be activated.

Another point is that it seems to me (only my gut feel - no quantitative analysis) that the house batteries are not holding their charge as long as they did even a few months ago. We used to be able to go on the hook for 12+ hours on battery only (before having to start the generator) and never drop to 12VDC. Now we get to 12VDC in under 8 hours. And nothing has changed that I can think of in our usage or the DC loads.

So like you said, I am becoming suspect now of my house batteries. They are only from 2020, so not that old. But if they were improperly stored/charged/discharged/etc. they very well may be near the end of their useful life.

Again, thank you so much for taking the time to post all your thoughts! Although I've worked around electricity most of my life (commercial power generation) I have a lot to learn about how it actually applies in my new world on a boat!! Especially on the 12VDC side of the house! Thanks again!!

[bud37]

A question from one power engineer to another........ How many batteries are in this house battery bank you are using and are they 6vdc or 12vdc ,also what is the amp hour rating of each battery. I know I said before I thought that 12.4 volts was low and it is but without knowing what those batteries were capable of we cant tell what to expect from them. If you calculate the draws you have from that bank in amp/hours then you should be able to estimate where the voltage should be from full after a reasonable time frame. See below chart....

Lead-Acid-Battery-Voltage-Charts-Image-10.jpg

[Midnightsun]

Problem with voltage readings is they are fine for giving a good "estimate" on how much juice is left however these reading must be taken after power has been drawn from them to eliminate the residual charge voltage. Also, I have seen batteries measure 12.6 v yet were unable to supply power to ant decent draw as they were a their end of life.

I also suspect worn down battery to be your issue. A good old fashion toaster test can reveal a lot. Not to mention any idiot can use one, even me. I also have a very expensive digital tester however the toaster, although they are old fashion, has proven better in some cases.

[KyleR]

A question from one power engineer to another........ How many batteries are in this house battery bank you are using and are they 6vdc or 12vdc ,also what is the amp hour rating of each battery

Thanks for the reply! There are two 12V batteries in the house bank. Attached is a photo of the label with the specs as well as the voltage chart I am using since these are flooded lead acid types (not sealed). That was one of the other "gotchas" I discovered when going through the systems. These batteries had a label that said "Remove this label when installed to monitor electrolyte level" (or something like that). The label had never been removed (i.e. no way to check level with label on) and the batteries had been installed in 2020. So again they were definitely neglected. Thankfully when I checked the level everything looked good - with no plates uncovered.

So based on the flooded battery chart I have been limiting the low-end voltage to right at 12.1VDC - at least as best as I can read using the analog meters installed on our boat.

[KyleR]

Also, I have seen batteries measure 12.6 v yet were unable to supply power to ant decent draw as they were a their end of life.

Definitely! Reminds me of weak starting batteries that show good voltage but when put under a load they have nothing left to give!

A good old fashion toaster test can reveal a lot

Do tell! I've never heard of a "toaster test". How's it performed? Do I need a 12VDC toaster? Is it like the load testers used by the auto parts stores - just using a toaster wired to the battery in some fashion?

Thanks for your reply!!

[bud37]

The chart is somewhat lower than I would be happy with. While all of the above may be true in certain cases, remember if you don't add up your loads and size the new bank properly the same thing may happen again. I will see if the deka site has the amp hours clearly stated. The manufacture date is stamped in the battery case edges.


Like all things there needs to be found the base line of where you are now.....don't just assume the batteries are bad, they may not be, only 2 years old.....they can be removed and tested at some auto parts places.
Most battery maintenance says not to pull lead acid batteries down below 50% for longevity....something to keep in mind.

[bud37]

Ok...it appears according to Deka those batteries are 105ah each ....so in parallel they will have 210ah. Considering that, 50% would be 105ah left........that will allow you to pull that much from them.
One fridge at 8 amp draw running for 15 minutes twice an hour would pull 8 amps for the 1/2 hour....4 amps for the hour....therefore 4ah......divide 105ah by 4ah = 26 hours of use. This is a rough estimation at best but will give you an idea. You will have to calculate what your real loads are...try to track the voltages using a DVM, the dash gauges can be quite erratic....

There are other ways to calculate using watts but this will get you close enough.........good luck man.

Edit for bad math....