Battery life

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russ

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Can I keep my fridge turned on whilst moored for 3 days without shore power and not discharge batteries?
Normally leave it on but only overnight before leaving the next day.
The batteries can only be used together, no 1 or 2 switch just on/off.:confused:

Or should the engine run for 1/2 hour each day to charge them?
 
russ said:
Can I keep my fridge turned on whilst moored for 3 days without shore power and not discharge batteries?
Normally leave it on but only overnight before leaving the next day.
The batteries can only be used together, no 1 or 2 switch just on/off.:confused:

Or should the engine run for 1/2 hour each day to charge them?
Click to expand...

Lots of variables. How big is your battery bank, how efficient is your fridge insulations, what is the ambient temperature in the cabin etc etc
 
Running the engine for half an hour won't do much!!

Use only one bank, so you know the engine will definitely start, and try running the fridge in the daytime only, as it's cooler at night, so any losses will be less.

That'll double your battery life in one fell swoop... :D
 
Russ, go for a run on the boat.

The moorings are marked with your name so no one else can take them.

We are heading to the boat shortly, can't wait!!

I will be leaving the domestics on one battery only, have an big cooler box full of ice for the drinkies :D
 
Russ, I have just increased my domestic capacity to 3x115ah. I talked through the demands of my domestic side, and I have purely electric cooking. My electrician said that the fridge will draw circa 20 amps total per day. I have a Waeco Coolmatic. So if you factor in something like a 25% contingency then you can work through from there, but I would be happy to leave my current system on for 3 days without top-up running only the fridge.

My engine side is wired-up separately, so I am OK if the domestics draw down, so I can still start my engines.

With the battery condition indicator, overnight leaving the fridge on, using the Hifi. lights, and TV, water pump, Microwave for 30 mins, our batts dropped to 5/8 max. As I motored every day, then they charged back to 3/4. Rafiki has a 2.5kW inverter so I can run most things. Did not use the kettle, but it will boil off the inverter.
 
My electrician said that the fridge will draw circa 20 amps total per day. I have a Waeco Coolmatic. ?



Approx 5 amps per hour from normal boat fridge when actually cooling ?
 
oldgit said:
My electrician said that the fridge will draw circa 20 amps total per day. I have a Waeco Coolmatic. ?



Approx 5 amps per hour from normal boat fridge when actually cooling ?
Click to expand...

Mine runs at 4 amps for about 10 mins per hour. I think the Maths wok out ok.
 
Last edited:
I find a single 80w solar panel is enough to keep a fridge running 24/7 with enough spare power left over to keep your battery bank topped up too, and you can buy them for about £100

Could be a wise investment if you are away from shorepower for any length of time as you dont have to worry about your batteries running flat
 
Brit

"I find a single 80w solar panel is enough to keep a fridge running 24/7 with enough spare power left over to keep your battery bank topped up too,"


80w panel delivers a max of about 5a amps on a really really sunny day,bit optimistic to run your fridge and charge battery ?
 
rafiki_ said:
Mine runs at 4 amps for about 10 mins per hour. I think the Maths wok out ok.
Click to expand...

My Waeco at 17 deg runs for 3 mins ON and 8 mins OFF.
Initial current is 6A and near the end has reduced to 4.5 A (don't ask why).
Let's say an average of 2.5 A/Hr = 60 per day (much more when it gets hot) which means a 3 X 110 A/H (probably only 300) when discharged down to 50% lasts for 2.5 days (if you are lucky)

My experience of batteries over 30 yrs of buying them has proved to me that they never produce what is quoted, even when new.
 
Teddy said:
My Waeco at 17 deg runs for 3 mins ON and 8 mins OFF.
Initial current is 6A and near the end has reduced to 4.5 A (don't ask why).
Let's say an average of 2.5 A/Hr = 60 per day (much more when it gets hot) which means a 3 X 110 A/H (probably only 300) when discharged down to 50% lasts for 2.5 days (if you are lucky)

My experience of batteries over 30 yrs of buying them has proved to me that they never produce what is quoted, even when new.
Click to expand...

Agree completely. Most charging systems rarely achieve 85% and ideally shouldn't drain below 50 % so only about one third rated capacity actually available. Discharge below 50% is ok but will shorten life of battery.
I also have 3 x 100 amps so work on basis that I can use around 100A/h before recharging by whatever means - and my Engel fridge uses about 48A/h per 24 hours. We switch fridge off at night which is a big saving and also stops it keeping us awake!
 
We have a couple of 105 dedicated domestic batteries, the starter is completely seperate. We have managed a few days without running the engine or being plugged into shore power before but the batteries were suffering towards the end.

That said we have tried to cut our power consumption. We have all LED lighting and low powered appliances. We leave the fridge on 24/7 to keep the beer cold. The fridge is our main power consumer followed by the Webasto diesel heater. The other bits and bobs dont use too much.

We do tend to cruise each day which does help keep the batteries charged and during the week the batteries are being looked after by our battery charger so they are as full as they can be when we set off.
 
I'm glad this thread was started as I face the same issues, if not greater.

Running 2 x 75ah leisure batteries charged whilst cruising by a meagre 20hp Honda OB with 12A charging coil (at max revs), I find that using my 40w Waeco fridge whilst moored for periods of up to 20 hours, one fully charged battery will drop to less than 11.9V and then it's time to switch batteries.

I too need a solar panel purely to reduce battery drain when moored up when the fridge is on. I guess there's a zillion threads on this subject on the MoBo forum but could someone quickly suggest a size of solar panel that might meet mine (and others) needs?
 
oldgit said:
My electrician said that the fridge will draw circa 20 amps total per day. I have a Waeco Coolmatic. ?



Approx 5 amps per hour from normal boat fridge when actually cooling ?
Click to expand...

It's common to confuse A and Ah but your electrician meant to say that the fridge will draw 20 amp hours (written as 20Ah) per day.

That's amps x hours, not amps per hour. 20Ah per day equals an average current of 0.833 amps.

To get Ah multiply the average current times the length of time in hours.

So after 3 days the OP will have used 60Ah. If he has 200Ah of battery capacity, they will be 70% charged, which is fine.

Generally you don't want to take lead acid batteries below 50% as the life is shortened. You can get about 500 cycles to 50% from deep cycle batteries, (and maybe 5000 cycles to 90%.)
 
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