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Old 15-10-2018, 16:02   #1
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Low voltage cutout for freezer

I'm thinking of installing a low voltage cutout switch dedicated to the freezer, which happens to have the biggest share of power consumption on the boat. It was installed for the original owner as per the manual, which specifies a direct connection to the battery, not on a panel switch.

I'm seeing a board on ebay with programmable shut off voltages of either 10, 10.7, 11.4, and 12.1 while the reconnect voltage must be higher, with an additional option of 12.8V

https://www.ebay.com/itm/12V-10A-Aut...d=192615865371

Any suggestions are appreciated
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Old 15-10-2018, 16:40   #2
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Re: Low voltage cutout for freezer

How about this one..

https://www.bluesea.com/products/763...age_Disconnect
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Old 15-10-2018, 16:54   #3
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Re: Low voltage cutout for freezer

https://m.ebay.com/sch/i.html?sid=sb...ons.sales.usa4
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Old 15-10-2018, 17:25   #4
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Re: Low voltage cutout for freezer

Check to see what your low voltage cut out is now.
A lot of fridge controllers do have a low voltage cut out already.
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Old 15-10-2018, 19:01   #5
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Re: Low voltage cutout for freezer

Many device LVDs are so low they must not be designed to protect the bank, just their device electronics.

Adjustable is best.
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Old 16-10-2018, 10:08   #6
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Re: Low voltage cutout for freezer

Danfoss usually cuts out at 10.4 and in at I think 11.7.

Remember two things, this is at the controller, not the bank, and you donít want any high amp loads, windlass, winch or whatever needlessly cycling your controller.
So if you set one close to 12V to protect the bank, then itís likely it will be excessively power cycling the compressor controller.
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Old 16-10-2018, 10:16   #7
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Re: Low voltage cutout for freezer

If you live aboard how about a low voltage alarm instead. Do you really want to shut off your freezer and spoil your food or do you want to know about a situation and act to solve it?
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Old 16-10-2018, 10:26   #8
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Re: Low voltage cutout for freezer

It will likely cause the freezer to short cycle. As it attempts to start the voltage will drop causing the shutoff. Once off, the voltage will rise enough for another attempt. It can eventually burn out the electronic inverter control powering the compressor.
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Old 16-10-2018, 13:25   #9
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Re: Low voltage cutout for freezer

No, compressor fridges should not be pulling much current.

AH per day overall sure, especially as freezers.

But amps are low, usually not enough to pull V down.

And yes, they are a very low priority load compared to safety / navigation gear.

Alarms set a bit higher than the LVDs are great, but are no substitute for cutoffs for when you aren't around.

Obviously greater energy inputs and / or a better or bigger House bank is required if such issues are chronic.

As might be a separate high-amps bank for huge loads.

But setting a user-adjustable LVD on that circuit can be helpful in the meantime, and later for worst-case, rarely needed protection.

Start out setting it at 11.8V or so, tweak down if needed. If 11.2-3V is still too often, then the systemic solutions above should increase in priority.
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Old 16-10-2018, 13:48   #10
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Re: Low voltage cutout for freezer

Quote:
Originally Posted by Thumbs Up View Post
It will likely cause the freezer to short cycle. As it attempts to start the voltage will drop causing the shutoff. Once off, the voltage will rise enough for another attempt. It can eventually burn out the electronic inverter control powering the compressor.


Actually, he is correct, that is why Danfoss has the two voltages so far apart.
If you have BIG wire to the fridge controller, you donít get much voltage drop, most people donít though and get more drop than you may imagine.

I gotta go with the Alarm making the most sense to me. I have Blue Sea M2 meters, and they have alarms you can set.
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Old 16-10-2018, 14:18   #11
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Re: Low voltage cutout for freezer

I'm using this low voltage cutoff switch in another application, and it has worked reliably for two years aboard: http://www.aprsworld.com/apo3/images/apo3_manual.pdf

It will do the job, provided your current load never exceeds 20 amps.

If the voltage rises above the cutoff, it reactivates power immediately. This could conceivably cause the switch to "walk down" your battery if the threshold is set too low:

- voltage drops below switch threshold, switch turns off
- after load is removed, battery resting terminal voltage rises above the switch threshold
- switch turns back on
- repeat in a loop until the resting battery terminal voltage is "walked down" to the set voltage.

Just be careful not to select a threshold voltage that depleates the battery beyond your tolerance. The threshold voltages available are: 11.8, 12.1, 12.7, 13.05 volts DC. I personally wouldn't set the threshold below 12.1 volts, which is the resting voltage of a lead/acid battery at approx. 50% state of charge.
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Old 16-10-2018, 14:28   #12
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Re: Low voltage cutout for freezer

Quote:
Originally Posted by dave777 View Post
I'm thinking of installing a low voltage cutout switch dedicated to the freezer, which happens to have the biggest share of power consumption on the boat. It was installed for the original owner as per the manual, which specifies a direct connection to the battery, not on a panel switch.

I'm seeing a board on ebay with programmable shut off voltages of either 10, 10.7, 11.4, and 12.1 while the reconnect voltage must be higher, with an additional option of 12.8V

https://www.ebay.com/itm/12V-10A-Aut...d=192615865371

Any suggestions are appreciated
First suggestion: Wire it to a circuit breaker, as it should be for safety and convenience. I HOPE there is at least a fuse, close to the battery, of a size to protect the wiring. The idea of having a freezer that can not be disconnected from power without pulling wire from a battery post is just plain dumb.

Any manufacturer who specifies a direct battery connection has no business selling products to the marine market, IMO. It's bad practice all the way round.
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Old 16-10-2018, 16:42   #13
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Re: Low voltage cutout for freezer

How about going the other way and simply increasing battery capacity?
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Old 16-10-2018, 17:04   #14
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Re: Low voltage cutout for freezer

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Originally Posted by a64pilot View Post
Actually, he is correct, that is why Danfoss has the two voltages so far apart.
If you have BIG wire to the fridge controller, you donít get much voltage drop, most people donít though and get more drop than you may imagine.
Depending how wires are routed, you might be able to get around that problem by inserting/installing the LVD closer to the battery end of the circuit, rather than right next to the compressor.

If there's space, just mount the LVD behind the breaker panel. Run short, heavier gauge jumpers from the fridge breaker and ground bus to the battery side of the LVD, and connect the existing (smaller) wires running to the fridge to the load side of the LVD. Then, even if there's a big voltage drop at the compressor end during startup, the LVD won't see it (it'll see something much closer to the battery terminal voltage).
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Old 16-10-2018, 17:25   #15
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Re: Low voltage cutout for freezer

Quote:
Originally Posted by a64pilot View Post
Check to see what your low voltage cut out is now.
A lot of fridge controllers do have a low voltage cut out already.
^^^^
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