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Fridge keeps cycling: battery13V

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jeb View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jeb Quote  Post ReplyReply Direct Link To This Post Posted: 24 June 2020 at 11:44
I charged to 6 mm2 cables on my 4
H400. No problem to get thrue the pipe and works fine. You can also change the cutoff voltage on the compressor. It’s described in the manual. Google Danfoss bd35.
Jesper
Hanse 400e
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H8jer View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote H8jer Quote  Post ReplyReply Direct Link To This Post Posted: 07 July 2020 at 20:49
Originally posted by Captain Cook Captain Cook wrote:

2,5 mm2 is not enough. The original cables to the fridge in my boat is 6 mm2, and at that gauge they had a voltage drop of 0,9 V at the compressor. I used the old 6 mm2 cables to trigger a relay, which I fed with 25 mm2 cables. See photo.
The fuse for the fridge is 15A, and 15A*12V is 180W. You can find multiple pages on the internet, where cable dimensions are calculated. This page tells that you need 9,84 mm2 if the cable is 5 meters. https://solcelle.dk/kabel_dimensionering_for_12v.htm
Isotherm/Danfoss compressors do not work well with voltages below 12V.
https://www.myhanse.com/isotherm-fridge-failure_topic4779_page2.html


How many amps are your setup using?

I have the same Isotherm Dual Volt system. It is using Danfoss bd35 compressor which is rated for 35 watt nominel but 44 watt in "turbo".
Mine uses 5 amps (5Ax13.5volt=) 67watt. The question is then - do I lose a lot due to too thin wires?

Hanse 370#487 30HP 3-cabin
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S&J View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote S&J Quote  Post ReplyReply Direct Link To This Post Posted: 07 July 2020 at 21:31
I only used the 2.5mm cables to try to verify if the cables were at fault or the fridge controller.
I believe I had a bad connection somewhere as after replacing the short connecting wire from the fridge to the main wire from the Wurth panel everything seems ok.

Not convinced I won't have this problem again as negative cable was corroded/oxidized and looked black.

I am interested in the relay but still wonder how you get the new (heavy duty) cables from the battery to the fridge.  In the 385 to here is no conduit under the galley sink.

Also concerned that the fridge protection mechanism did not shut the fridge off completely but just caused repeated restarts.

My fridge seems to draw 4-5 amps when the compressor is on but I keep it on the lowest setting which still makes ice cubes and it doesn't run very long so I'm happy with overall power usage.


Edited by S&J - 07 July 2020 at 21:42
H385 #351 Ningaloo UK south coast; Scotland 2020?
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Captain Cook View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Captain Cook Quote  Post ReplyReply Direct Link To This Post Posted: 08 July 2020 at 01:59
I did warn the members in an earlier post, that you cannot blindly trust informations on the internet, not even the wise words from an old-timer like Captain Cook.
When I used 25 mm2 cable to feed my compressor, it was because I had two pieces of cheap starter cables available. Such chinese cables are made of more aluminium than copper, and the effective mm2 is most likely half the stated thickness. Anyway it is an upgrade from the 6 mm2, and the voltage drop of 0,9V changed to something like 0,1-0,2 V.
If your fridge is equipped with the Danfoss DB35 compressor, it consumes max 79 W to compress the R134A fluid/gas, and a few W to reload the capacitor, work the thermostat and electronics. The lightbulb uses 5 W. (DB50 uses 108W). All in all the maximum possible power draw should not exceed 90W. At 12,5 V that uses 7,2 A. In theory a cable 6 meters in lenght then should be dimensioned to 5,67 mm2 to carry the current to the consumer with a voltage drop of less than the maximum 2%.
So when Hanse put a 6 mm2 cable in my boat, why do I complain?
I do complain, because I did measure a voltage drop at the compressor of 0,9 V, and I do not care if it is due to a poor quality of the cable, or if it maybe is 8 meters long instead of 6. (Or if the DB35 uses 110W).
As I said in page one of this thread, The Danfoss do not like less than 12,5 V, and in the link in my post of june 14th, you can read:
"So keep in mind that if the voltage at the controller is less than 11.8v but above 10.4v when you initially power up the system, the compressor will not start but there will be no one-flash alarm! The compressor will only start once the voltage has risen above 11.8v."
My advice to you is to measure the voltage at the house battery, which should be 12,7 V or more, and then measure the voltage at the compressor, first when it is idle, an then just when the fridge is starting. In the moment of start, the capacitor helps keeping the voltage, but if you experience a voltage drop of more than 2%, you should use thicker cables.
My autopilot and chartplotter are also fed by 6 mm2 cables and here is of course also a voltage drop of 0,5-0,7 V. Therefore I already a few years ago mounted a set of high quality 16 mm2 cables from the batteries to aft. The work is still in progress, I still need to put cables up the steering column.
You could say, that it is not important, if there is a voltage drop at the chartplotter - so what???
Well, if you have worn your batteries down to 11,3 V, while cruising at night in the swedish "skärgård", and the voltage drop of 0,9 V means that your plotter only gets 10,4 V, then it gets very dark in the cockpit when the plotter turns off. (Your engine is dead of course).
:Cook the Captain



Edited by Captain Cook - 08 July 2020 at 02:40
Freya Hanse400 #27 from 2006, 40HP Yanmar 3JH4E, Teak deck, 3-blade Flexofold, Aries LiftUp Windvane, Exturn 300, Jefa DD1,Simrad NX40,Icom M802(SSB)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote H8jer Quote  Post ReplyReply Direct Link To This Post Posted: 08 July 2020 at 09:13
Just to further clarify what power consumption is expected to be used by the fridge:

After many pictures it is certain the compressor is the BD35F from year 2007/2008.
This is the current draw according to a 2008 datasheet:


It is difficult to understand the relation ship between temp/rpm and amps.
It might be a DeltaTemp between temp feed to the compressor and what is leaving it. Thus the different COP's getting lower when the feed temp also gets lower.

Anyway the RPM is not known for me and we don't know DeltaTemp so the takeaway must be that it does not consume more that 6.5 amps.
With addtional power for fan/controller and loss in cable transmission I would think that the nominal usage of 5 amps is acceptable.

I alwas see about 5 amps so I guess the speed is fixed. If the fridge needs more cooling the compressor just run more often.


Hanse 370#487 30HP 3-cabin
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