What amp battery charger to run a 12v fridge?

[Herdwick]

We just bought our first narrowboat and have a very bare bones set up. Since the only mooring we could find In the area was at a marina, we want take advantage of the shore power and run our little 12v LEC Shoreline Fridge 24/7. We live close by and visit several times a week and want to just leave food in the fridge and not empty it each time we leave.

 

Our boat came with two 100watt solar panels and an old 10amp battery charger. On sunny days it’s fine. But at night or cloudy days, the two 110ah leisure batteries die a slow death.

 

Should the two leisure batteries be able to keep the fridge going overnight even without a charger?

 

What size battery charger should I have to run the fridge 24/7 on days with no solar? Should 10amp be enough? Or do I need 15,

20, or 30?

 

Apart from the fridge the only other 12v use is led lights and water pump.

 

Oh, we just bought two brand new 110ah leisure batteries. So we know they are fine.

 

Thanks. Any advice is appreciated.

 

 

[Tracy D'arth]

I ran a boat on an 8 Amp charger for 14 years, with no solar.

[Jen-in-Wellies]

The 10A charger should suffice. Don't know about that particular model, but a lot of fridges seem to take around 5A at 12V to run and run for maybe 50% of the time, with a high inrush current for a fraction of a second when the compressor starts up. A 10A charger will cope with this and should keep the new batts happy. The power consumption of the fridge depends on a lot of things, even for the same make and model. How well ventilated the area around its heat exchanger coils are, how good condition the door seal is in, but the above numbers shouldn't be far off.

Jen

[Pie Eater]

Do you keep the fridge on a low setting?

[nicknorman]

10A charger should be quite adequate. A fridge typically uses about 35-40Ah per day, so your 2 x 110Ah batteries should last a couple of days IF they are properly fully charged at the start. If they are not properly fully charged they can lose capacity very quickly, in just a few weeks. Oh that assumes that your fridge is a compressor type, not a 3 way (gas, 12v and mains absorption type).

 

It sounds to me like the devil is in the detail of charger behaviour, solar controller settings, wiring integrity and battery health (despite being new).

[Tony Brooks]

Is the fridge thermostat cutting the motor out and back in as required. Old fridges can lose gas so the motor runs practically all the time.

 

There is something odd. 100 Ah of usable capacity would typically run the fridge with nothing else running for about 2 days. How are you measuring the batteries' state of charge? It sounds like under charging to me.

 

To the best of my knowledge Shoreline never marketed an absorption fridge so it's a compressor model.

Edited April 26, 2021 by Tony Brooks

[Richard10002]

To the OP. Leave your charger running from shore power,  and it will easily keep your batteries topped up, whilst they are powering the fridge.

 

If the batteries were to need 10A all the time, (which is highly unlikely), they would be getting 240Ah per day, which is of the order of 10 times what the fridge will use.

[David Mack]

3 hours ago, Herdwick said:

 But at night or cloudy days, the two 110ah leisure batteries die a slow death.

 

Should the two leisure batteries be able to keep the fridge going overnight even without a charger?

...

Oh, we just bought two brand new 110ah leisure batteries. So we know they are fine.

Was the slow death with the old batteries or the new ones? A pair of reasonable condition 110AH batteries should have no trouble with the fridge for overnight - good batteries would achieve 2-3-4 days. But if the batteries are knackered (technical term) then overnight may be too much for them.

New batteries will very quickly lose capacity if you don't fully charge them once a week or so. If your new batteries won't run the fridge overnight, then you may already have damaged them. 

[Herdwick]

The old batteries would be dead each morning and the fridge red low voltage light blinking even with the 10amp charger on.

 

I didn’t want to risk killing the new batteries, so hadn’t ran the fridge yet since installing them.

 

Last night did first trial run with the new batteries:

 

The new batteries seem to be holding at 12.7volts (per the solar controller reading) throughout the night - with the fridge on AND the 10amp charger on.

 

Next time we overnight on the boat I will see what happens if I don’t turn the charger on. How low can the batteries safely get without damaging them? 12.2volts? Or?

 

Thanks for all the comments and advice!

 

 

[Momac]

I generally have the battery charger on  full time . The charger is designed to  be used in that way.

When away from shore power in summer I work on 24hrs  without charging per 110Ah battery with the fridge being by far the greatest demand. I very hot weather  the fridge will work harder of course .

 

Your charger is keeping up with the fridge .

 

I try not to go below 12.4V under no load.

 

 

[Tony Brooks]

29 minutes ago, Herdwick said:

The old batteries would be dead each morning and the fridge red low voltage light blinking even with the 10amp charger on.

 

I didn’t want to risk killing the new batteries, so hadn’t ran the fridge yet since installing them.

 

Last night did first trial run with the new batteries:

 

The new batteries seem to be holding at 12.7volts (per the solar controller reading) throughout the night - with the fridge on AND the 10amp charger on.

 

Next time we overnight on the boat I will see what happens if I don’t turn the charger on. How low can the batteries safely get without damaging them? 12.2volts? Or?

 

Thanks for all the comments and advice!

 

 

 

Was that 12.7V in daylight or the dark. If the former then its the solar charging voltage and in no way can infer the state of charge. If the solar controller displays and sort of state of charge reading my advice would be to ignore it and use rested voltage in the dark.

[Herdwick]

That 12.7 is in the dark. During the day it shows up to 13.9.

 

Thats with the new batteries. With the old, it would also show 13.9 when sunny, and quickly drop when sun went down even with the charger on. It would go down to 10.5 by morning. Lol

 

I was never sure if the charger was working, but with the new batteries it seems to be holding at 12.7 (sometimes 12.6 or 12.8) at night with the fridge on and the charger on.

 

The previous owner never used the charger (didn’t even know it was there as it’s mounted under a cabinet out of sight) and ran the engine in morning to recharge. I suspect he killed the batteries a while ago.

[Detling]

12.7 with a charger on is to low Any charger would have a float mode over 13 volts and a basic charger would be nearer 14 volts. so it suggests the charger is not functioning, or not connected. I think sterling have a habit of putting lots of LED's on its products, if so there may be a clue there otherwise follow the wires and check the fuse. A multimeter may help, both with the fuse and measuring the output terminals of the charger with one wire disconnected (or fuse removed).

[GUMPY]

I would buy s new charger as this one doesn't sound up to the job, my car charger exhibits the same voltage level when connected to the car over a long period.

Something like this should be OK they come in higher power versions as well.

https://www.portablepowertech.com/product/premium-15a-12v-battery-charger/

[Richard10002]

On 27/04/2021 at 11:14, Herdwick said:

That 12.7 is in the dark. During the day it shows up to 13.9.

 

 

On 27/04/2021 at 11:14, Herdwick said:

 

I suspect he killed the batteries a while ago.

 

I suspect the charger died during his ownership as well  

[LadyG]

On 26/04/2021 at 22:28, Richard10002 said:

To the OP. Leave your charger running from shore power,  and it will easily keep your batteries topped up, whilst they are powering the fridge.

 

If the batteries were to need 10A all the time, (which is highly unlikely), they would be getting 240Ah per day, which is of the order of 10 times what the fridge will use.

Older fridges, like mine are very demanding, I'd guess 50ah per day. 

[Murflynn]

2 hours ago, LadyG said:

Older fridges, like mine are very demanding, I'd guess 50ah per day. 

 

which is nowhere close to 240Ah. 

what exactly is your point?

[Alan de Enfield]

2 minutes ago, Murflynn said:

what exactly is your point?

 

Why break the habit of a lifetime, there never is a point. It's just random irrelevant waffling.

[Tony Brooks]

52 minutes ago, Murflynn said:

 

which is nowhere close to 240Ah. 

what exactly is your point?

 

Well the OP should not be considering using 220Ah (2 x 110) regularly. More like 110 Ah assuming no sulphation and true full charge, neither of which are likely. With no other electrical use that only gives 2 days use or maybe 3 days with a modern fridge.

 

I think two of us have implied 50A is probably a safe assumption and LadyG has just confirmed that.

[nicknorman]

10 hours ago, Tony Brooks said:

 

Well the OP should not be considering using 220Ah (2 x 110) regularly. More like 110 Ah assuming no sulphation and true full charge, neither of which are likely. With no other electrical use that only gives 2 days use or maybe 3 days with a modern fridge.

 

I think two of us have implied 50A is probably a safe assumption and LadyG has just confirmed that.

I think the 240Ah figure came from 10A charger running for 24h.

 

Anyway, it sounds like the charger is faulty.

[Richard10002]

2 hours ago, nicknorman said:

I think the 240Ah figure came from 10A charger running for 24h.

 

Yes... I said that the OP could leave the boat with the fridge on because, if the batteries were to demand the full 10A for 24 hours, that would be 240Ah, which would more than cover whatever was used whilst leaving the boat with the fridge on.

 

I would add that, once the batteries are "full", they would only draw whatever was used by the fridge, and it wouldn't matter whether this was an old fridge using 50Ah per day, or a newer fridge using 25Ah per day.

 

I also subsequently reached the conclusion that the charger is almost certainly faulty  

 

 

[Tony Brooks]

1 hour ago, Richard10002 said:

 

Yes... I said that the OP could leave the boat with the fridge on because, if the batteries were to demand the full 10A for 24 hours, that would be 240Ah, which would more than cover whatever was used whilst leaving the boat with the fridge on.

 

I would add that, once the batteries are "full", they would only draw whatever was used by the fridge, and it wouldn't matter whether this was an old fridge using 50Ah per day, or a newer fridge using 25Ah per day.

 

I also subsequently reached the conclusion that the charger is almost certainly faulty  

 

 

 

Which after re-reading the topic and noticing the vital part I missed I totally agree with.

[Ronaldo47]

I have the 1940 edtion of a book.on accumulator charging. It says that discharge below 1.8V per cell (10.8V for a nominal 12V battery) results in the spongy  lead sulphate that is created in the normal course of discharge, assuming a crystalline form. This crystalline form  is essentially non-conductive, meaning it is difficult to convert back to lead when charging. It does mention that  batteries for different applications have slightly  different acid concentrations, and this  results in slightly different voltages, but I think the basic chemistry of lead/acid  batteries is no different today.

 

 

 

 

 

 

Edited May 1, 2021 by Ronaldo47
typo

[Tony Brooks]

43 minutes ago, Ronaldo47 said:

I have the 1940 edtion of a book.on accumulator charging. It says that discharge below 1.8V per cell (10.8V for a nominal 12V battery) results in the spongy  lead sulphate that is created in the normal course of discharge, assuming a crystalline form. This crystalline form  is essentially non-conductive, meaning it is difficult to convert back to lead when charging. It does mention that  batteries for different applications have slightly  different acid concentrations, and this  results in slightly different voltages, but I think the basic chemistry of lead/acid  batteries is no different today.

 

It does that whenever you discharge a LA battery to whatever level, even just 5% discharged, if you don't recharge it ASAP. it's the sulphation we keep on about. The longer its left discharged and the deeper the discharge the worse the degree of sulphation.

[blackrose]

On 29/04/2021 at 09:09, Detling said:

12.7 with a charger on is to low Any charger would have a float mode over 13 volts and a basic charger would be nearer 14 volts. so it suggests the charger is not functioning, or not connected. I think sterling have a habit of putting lots of LED's on its products, if so there may be a clue there otherwise follow the wires and check the fuse. A multimeter may help, both with the fuse and measuring the output terminals of the charger with one wire disconnected (or fuse removed).

 

I used to have one of those Sterling pro-budget chargers. It should be putting out 14.4v max and sit on 13.6v on float.