Some refrigeration questions

[goboatingnow]

I have a BD35 air cooled fridge , I notice at high ambients ( 30 degrees C) my compressor controller will cycle the compressor on and off every 10 seconds or so. I presume this is where the fridge struggles to get down to temp to protect the compressor. This is evident during the day when the fridge is being used a lot. At night I can here the fridge thermostat click in and out


Then on the other hand my friends boat has a fridge which seems to run continuously for over a hour before turning off for 30 minutes. He finds this is running his batteries down at night , both his fridge and mine draw about 5.5 A when running

At night mines runs quite infrequently maybe every 5-7 minutes for about 30 sec

His was recently re-gassed and his evaporator box has frost over all of it.

[boatman61]

Sounds like you should check your seals, keeping the fridge as full as possible also helps.
Personally I prefer the old top opening cold boxes with a spillover tray plumbed in.

[Bowdrie]

Are the thermostats on both of the systems of the same brand/model?
His may have a different "differential" setting than yours.
Or, a simple thing like the mounting/securing/positioning, of the sensing bulb/tube can make a difference.
Trying to quantify differences of operation between different boats, (with different usages,) is difficult, just to many variables.

[sailorboy1]

every 10 seconds is not enough to change temperature in box

you have a problem with your controller, wiring, or unit control module IMO

I would start with wiring to be sure it isn't cycling due to a low voltage AT THE CONTROLLER (don't take the caps personal)

[michaeld]

I had a similar problem, and it was a faulty fan.

[Bill O]

What brand do you have and what type/size evaporator plate?
Do you have a variable speed controller on the power module or are you running at a set rpm? Need more info on your system.

Hard to tell by your brief description, but your friends system may have had too much refrigerant added to it.

A 5.5 amp draw would get me to assume you are running at 3000 or 3500 rpm. Dropping to 2500 or even 2000 rpm should still cool it down w/less amp power. Obviously it will need to run longer at the lower rpm to remove the same amount of heat from the box.

Have you checked the box seals lately. If the thermostat is kicking on every 10 min. you may have an air leak (letting in too much heat) or a bad thermostat. If you have a mechanical, could change it out for an inkbird electronic controller/thermostat fairly cheaply to see if it is the thermostat.

[goboatingnow]

I’m actually quite happy with my fridge ( the shorter cycling One ) it consumes approx 20AH over night ( from 8pm to 6 am. ) and it makes ice in 30 ambient. This is 4 hours run time over 10 hours , or around 40 :60 duty cycle. The panels have the batteries back by 11am and runs the fridge all day. My main point was the very different run time numbers.

My friends system is running for long periods ( 45 minute on 15 minutes off ) and he’s finding it drains his batteries over night. I’m going to put a logger on it to get a better picture ( he has 1 year old domestics ) his is consuming upwards of 50 Ah over night theoretically and he finds his batteries drop to 12.1V and the fridge drops out and stops running at all

[goboatingnow]

Originally Posted by Bill O

What brand do you have and what type/size evaporator plate?
Do you have a variable speed controller on the power module or are you running at a set rpm? Need more info on your system.

Hard to tell by your brief description, but your friends system may have had too much refrigerant added to it.

A 5.5 amp draw would get me to assume you are running at 3000 or 3500 rpm. Dropping to 2500 or even 2000 rpm should still cool it down w/less amp power. Obviously it will need to run longer at the lower rpm to remove the same amount of heat from the box.

Have you checked the box seals lately. If the thermostat is kicking on every 10 min. you may have an air leak (letting in too much heat) or a bad thermostat. If you have a mechanical, could change it out for an inkbird electronic controller/thermostat fairly cheaply to see if it is the thermostat.

My system is running at a set speed set by the resistor, I have a 18 “ by 10 “ evaporator and a BD35 compressor. Box is approx 2feet long by 1.5 feet wide and 2 foot deep ( standard Bavaria 36 so insulation will not be huge )

[JimsCAL]

This sounds like the refrigerant loop is fine. No problems with charge, compressor, etc. But the short cycling is not right and most likely controls related. Thermostat, cutouts, etc.

[Rumrace]

I’m sorry I can’t recall where I read it but it discussed this problem and the likely repair.
Apparently our typical fridge comes preset with unrealistic temperature we can change with the dial. You need a fridge tech to make two adjustments to some valve.
My fridge is 7 years old but get abused in winter storage in -30c weather so I accepted the possibility the sucker needed parts cause in ran often. It was recharged some insulation added to the back and one side and adjusted down to realistic ranges the compressor could achieve.
One trick to keep a fridge quiet is to fill it with water bottles. A fridge with nothing to cool works harder.

[Rumrace]

“Can’t change with dial” ^

[Bill O]

Do you know what resister you have installed? That would tell you what rpm you are running.

From you dim., your fridge size is ~6 cu and the same as ours.

For comparison, we have 2-3" of foam running w/a front opening door with a magnetic seal. The BD50 has a keel cooler w/a 42x10.5" evaporator (flat panel to fit around inside of fridge) and variable speed control for the compressor (frigoboat). If the air temp is >35C (>95F), we use ~40ah daily keeping the box temp ~1-2C (34-35F). The compressor will run for ~20-30 min/hr. We have "watt meter" as our logger.

When it's hot out we are going in the fridge often to get cold water and refilling the water jug w/ambient water.

Again, just the facts so you have a point of comparison.