Electrical ‘Brownouts’

[TeamRienza]

We used to be able to get EHU on the Oscar Wilde (Irish Ferries) for the 18 hour trip from Dublin to Cherbourg and more importantly for the return leg. It was not essential, but was useful in keeping the cheese and meats etc in good condition. We only exported teabags to the continent!

A new boat, W. B. Yeates, was put on the run about 2018. We continued to hook up when outlets were free, but on a few occasions the fridge defrosted en route. In fact on one run I thought perhaps my cable had been disconnected.

My current thoughts are that the fridge was not getting the full 230 volts. I have experienced this once or twice on a shared outlet and on a French site were I could not get the electric to function properly.

We have just returned today from a 3 week trip to France, and I did not bother with hook up either way. My question to those knowledgeable members is, will a prolonged period (18 hours) at less than 230 volts do any damage to the appliance?

Thanks,

Davy

 

[st3v3]

3 way fridge? No, it won't hurt.

Get yourself a victron inverter charger and your fridge won't know the difference

 

[trevskoda]

Turf the old 3 way and fit a 230v mini electric one plus a smart inverter, 2/3 big batteries and it will run 24 hrs no bother

 

[GeoffL]

When we've planned parking up for a day with no EHU and no wish to leave the gas running, we've left a couple of freezer blocks in the frozen food compartment of the fridge. Perhaps this would work for you also?
For info, the blocks freeze nicely when the fridge is on gas or 240v and don't thaw when on 12v. We store the van about half an hour from home and so the blocks also keep chilled food cool on the way to pick up the van and help bring the fridge cool down to temperature at the start of a trip.

 

[TeamRienza]

Thanks for the replies. Pleased to hear damage unlikely. As said we don’t regard the hookup as essential, just useful when on offer at no cost, but if not running properly, there isn’t much point. I know about the frozen bottles of water trick, but am happy to use gas when away from the van. Irish Ferries state clearly on their boarding pass that gas must be switched off and I wouldn’t dream of breaking the rule.
Sounds like my other option is to take up the very kind offer from Trev, who I take it, is to sponsor me throwing away my perfectly good fridge freezer and replace it with lots of expensive kit.

Davy

 

[trevskoda]

Thanks for the replies. Pleased to hear damage unlikely. As said we don’t regard the hookup as essential, just useful when on offer at no cost, but if not running properly, there isn’t much point. I know about the frozen bottles of water trick, but am happy to use gas when away from the van. Irish Ferries state clearly on their boarding pass that gas must be switched off and I wouldn’t dream of breaking the rule.
Sounds like my other option is to take up the very kind offer from Trev, who I take it, is to sponsor me throwing away my perfectly good fridge freezer and replace it with lots of expensive kit.

Davy

Fridge £50 inverter cost me £25

 

[r4dent]

3 way fridge? No, it won't hurt.

Get yourself a victron inverter charger and your fridge won't know the difference

Your fridge will not notice the difference, but the battery will!

An absorption (i.e. 3 way) motor home fridge / freezer uses use about 3 kWh per 24 hours.
Source https://www.dometic.com/assets/69/62/dometicrm10-rms10_opm_4445103085_emea18_01_2020-04_76962.pdf
page 34

Using 12v battery to supply the power (via an inverter) will require 3000 / 12 = 250 amp hours (ah) per 24 hours
Additionally, the inverter will require a further 10%, so you need about 275 ah per 24 hours.

A standard battery will provide 50% of the nominal battery capacity before it is flat.

Therefore, to run the fridge for a day (with it cold to start with) you will require a battery bank on 550 ah.

 

[Geek]

The way that a three-way fridge works is that it used heat to cool. That heat can be from 12v, from mains or from gas.
Normally, on a typical fridge, the gas uses about 300 watts, the mains about 240 watts, or the 12v about 120 watts.
If the voltage of the mains drops from 230v to (say) 180v (which is not unusual in a ship) the heating (and therefore cooling) power will drop by just over 40%.
If it drops to 110v, you've lost almost 80% of the normal mains power.
Won't do any harm to the fridge, but it won't be able to stay very cool.

 

[r4dent]

The way that a three-way fridge works is that it used heat to cool. That heat can be from 12v, from mains or from gas.
Normally, on a typical fridge, the gas uses about 300 watts, the mains about 240 watts, or the 12v about 120 watts.
If the voltage of the mains drops from 230v to (say) 180v (which is not unusual in a ship) the heating (and therefore cooling) power will drop by just over 40%.
If it drops to 110v, you've lost almost 80% of the normal mains power.
Won't do any harm to the fridge, but it won't be able to stay very cool.

Spot on.

The following is my attempt to out geek Geek

For a device of fixed Resistance (which is most things in a moho) the relevant formula is Power = (Voltage ^2) / Resistance
So at voltage 1 P1 = V1^2/R
& at voltage 2 P2 = V2^2/R
So when the voltage drops from V1 to V2
the loss % is (P1 -P2 )/P1
ie. [(V1^2/R) - (V2^2/R)] / (V1^2/R)
and since R is constant [V1^2 - V2^2] / V1^2)

To put this in context reducing voltage from 230v to 180v
the power loss is (230^2 - 180^2) / 230^2= (52,900 - 32,400) / 52,900 = 39%

and for the low voltage stuff in the Moho, reducing the battery voltage from 13v to 11v
the power loss is (13^2 - 11^2) / 13^2= (169 - 121) / 169 = 28%

Which is why if you cab battery is not fully charged it can't turn the engine over!

 

[st3v3]

Your fridge will not notice the difference, but the battery will!

An absorption (i.e. 3 way) motor home fridge / freezer uses use about 3 kWh per 24 hours.
Source https://www.dometic.com/assets/69/62/dometicrm10-rms10_opm_4445103085_emea18_01_2020-04_76962.pdf
page 34

Using 12v battery to supply the power (via an inverter) will require 3000 / 12 = 250 amp hours (ah) per 24 hours
Additionally, the inverter will require a further 10%, so you need about 275 ah per 24 hours.

A standard battery will provide 50% of the nominal battery capacity before it is flat.

Therefore, to run the fridge for a day (with it cold to start with) you will require a battery bank on 550 ah.

Don't forget, it is plugged into the mains, it's just that the mains is a bit sketchy

 

[trevskoda]

Your fridge will not notice the difference, but the battery will!

An absorption (i.e. 3 way) motor home fridge / freezer uses use about 3 kWh per 24 hours.
Source https://www.dometic.com/assets/69/62/dometicrm10-rms10_opm_4445103085_emea18_01_2020-04_76962.pdf
page 34

Using 12v battery to supply the power (via an inverter) will require 3000 / 12 = 250 amp hours (ah) per 24 hours
Additionally, the inverter will require a further 10%, so you need about 275 ah per 24 hours.

A standard battery will provide 50% of the nominal battery capacity before it is flat.

Therefore, to run the fridge for a day (with it cold to start with) you will require a battery bank on 550 ah.

Thats strange caus i did a bench test running 2 90ah truck batteries which fell to 12.2 in 24 hrs, after a short rest they lifted to 12.4 before recharging, my fridge uses less that one qtr of an amp when running which is about 5/10 mins every 20 mins or less.

 

[GeoffL]

Your fridge will not notice the difference, but the battery will!

An absorption (i.e. 3 way) motor home fridge / freezer uses use about 3 kWh per 24 hours.
Source https://www.dometic.com/assets/69/62/dometicrm10-rms10_opm_4445103085_emea18_01_2020-04_76962.pdf
page 34

Using 12v battery to supply the power (via an inverter) will require 3000 / 12 = 250 amp hours (ah) per 24 hours
Additionally, the inverter will require a further 10%, so you need about 275 ah per 24 hours.

A standard battery will provide 50% of the nominal battery capacity before it is flat.

Therefore, to run the fridge for a day (with it cold to start with) you will require a battery bank on 550 ah.

The way that absorption and compressor fridges work makes a huge difference. While an absorption fridge might require 3 kWh per day, a compressor fridge needs much less. For example, most under-counter fridges with an energy efficiency rating of "F" use between 115 kWh and 120 kWh per annum, or less than 330 Wh per day. At 12V this is 330/12 = 27.5 Ah, or about 1/10 the energy that an absorption fridge would need. So @trevskoda has a good point -- particularly if you have enough solar, do enough driving, or spend enough time on EHU to replace the charge expended keeping a mains fridge running and have 200Ah or more of leisure battery capacity.

 

[r4dent]

Thats strange caus i did a bench test running 2 90ah truck batteries which fell to 12.2 in 24 hrs, after a short rest they lifted to 12.4 before recharging, my fridge uses less that one qtr of an amp when running which is about 5/10 mins every 20 mins or less.

I suspect that it is a compressor fridge.

Power requirement is completely different for absorption and compressor fridges.

My figures relate to someone running an absorption fridge from 12v batteries using an inverter.