house battery charging

[RayM]

Hi There,

i have 3 x 150ah lead batteries on my boat. 1 for Cranking and 2 for House use.

i run two small fridges off the house batteries (60L each) with a 160w solar panel.

One fridge will stay on all night but the other will turn off and on intermittently.

Do I need a larger solar panel like 500w ?

or do i need to keep my lead acid cranking battery and change the two house batteries to deep cycle ?

Any advice will be much appreciated.

 

Kind Regards,

Ray

[Huxstang]

Need more detail.  What are the fridges or do you know power consumption.?  

How are they wired…separately to each battery or is their a common power bus.  

Fridges cycling on and off is normal behaviour, but if its shutting down most camping fridges have a low voltage cut off.  So it does come down to how its wired and how you are using things.

What is the state of your batteries?

do you have a multimeter?  

Measure your batteries at full charge ie with no draw then measure again before dark and see what the state of charge is on each one.

Do you need more solar…this is fairly detailed but the below is fairly long winded but for me I would not make any change until I fully understood the actual problem…as you have only given a small amount of information that does not allow all the issues to be unpacked.

Not sure if this will help but hopefully it will give you more understanding of how your batteries and solar work.

Your lead acid battery bank - assuming your only using house bank for fridges gives you (when new) 150 amp hrs of usable output (50% depth of discharge).  If you have discharged them deeply a number of times you have shortened their lifespan significantly.  Deep cycle batteries won’t give more useable capacity just a longer life for your depth of discharge.

Now whether your need more solar or different batteries depends on your actual draw really…if they are say Engel 60l fridges running as a fridge you would say around 2-4amp/hr draw…ie 192 amp hrs max in 24hrs.  Once they go to freezer you can expect more like a constant 4-6amps plus.  I use Engels as an example as they are one of the most efficient 12/24v compressors in use for 4WD/camping.  Some other brands will be more like 10amps plus.

Your 160w solar theoretically is putting out @ 8amps of current, although actual depends on many factors - age/cloud/clean/etc etc.  But you should expect @ 80amp of input into your batteries over the day. 

So during a theoretical 10hr daylight period your existing battery bank is not being reduced from its existing state of charge based on what two Engel fridges might use.  That means your current draw might be no more than 112 amp hrs where solar is not charging which is inside the theoretical capacity of your existing house bank.  I say theoretical because if you have deep discharged your batteries a number of times your actual capacity could be quite a bit lower.

However, that does not take into account any other draw such as lights/TV/ water pumps etc.  It all adds up.

PS I am not expert just done lots of remote area camping where I needed to be able to maintain power for extended periods so have taught myself a fair amount - helps that a mate is an electrical engineer and the other a electrical tech.

Personally I would put a smart shunt in so I could see the variables and actually understand what is happening before I charged batteries or solar panels.  Once you can see just how much you use and how much you generate you can make a much more informed decision.

Personally I would have one regardless as its the only way to reliably understand what is happening in your 12v system.  I use Victron IP65 Smart Shunts that you can read via blue tooth on your phone via their app (I have one Smart Shunt on my cranking/house lead acid bank and another on my lithium bank for trolling motor).  However if you have space the BMV-712 has a nice gauge that allows you to read it without a mobile device.   I would recommend Springers for the best prices in Brisbane.

 

[fatboy]

25 minutes ago, Huxstang said:

Need more detail.  What are the fridges or do you know power consumption.?  

How are they wired…separately to each battery or is their a common power bus.  

Fridges cycling on and off is normal behaviour, but if its shutting down most camping fridges have a low voltage cut off.  So it does come down to how its wired and how you are using things.

What is the state of your batteries?

do you have a multimeter?  

Measure your batteries at full charge ie with no draw then measure again before dark and see what the state of charge is on each one.

Do you need more solar…this is fairly detailed but the below is fairly long winded but for me I would not make any change until I fully understood the actual problem…as you have only given a small amount of information that does not allow all the issues to be unpacked.

Not sure if this will help but hopefully it will give you more understanding of how your batteries and solar work.

Your lead acid battery bank - assuming your only using house bank for fridges gives you (when new) 150 amp hrs of usable output (50% depth of discharge).  If you have discharged them deeply a number of times you have shortened their lifespan significantly.  Deep cycle batteries won’t give more useable capacity just a longer life for your depth of discharge.

Now whether your need more solar or different batteries depends on your actual draw really…if they are say Engel 60l fridges running as a fridge you would say around 2-4amp/hr draw…ie 192 amp hrs max in 24hrs.  Once they go to freezer you can expect more like a constant 4-6amps plus.  I use Engels as an example as they are one of the most efficient 12/24v compressors in use for 4WD/camping.  Some other brands will be more like 10amps plus.

Your 160w solar theoretically is putting out @ 8amps of current, although actual depends on many factors - age/cloud/clean/etc etc.  But you should expect @ 80amp of input into your batteries over the day. 

So during a theoretical 10hr daylight period your existing battery bank is not being reduced from its existing state of charge based on what two Engel fridges might use.  That means your current draw might be no more than 112 amp hrs where solar is not charging which is inside the theoretical capacity of your existing house bank.  I say theoretical because if you have deep discharged your batteries a number of times your actual capacity could be quite a bit lower.

However, that does not take into account any other draw such as lights/TV/ water pumps etc.  It all adds up.

PS I am not expert just done lots of remote area camping where I needed to be able to maintain power for extended periods so have taught myself a fair amount - helps that a mate is an electrical engineer and the other a electrical tech.

Personally I would put a smart shunt in so I could see the variables and actually understand what is happening before I charged batteries or solar panels.  Once you can see just how much you use and how much you generate you can make a much more informed decision.

Personally I would have one regardless as its the only way to reliably understand what is happening in your 12v system.  I use Victron IP65 Smart Shunts that you can read via blue tooth on your phone via their app (I have one Smart Shunt on my cranking/house lead acid bank and another on my lithium bank for trolling motor).  However if you have space the BMV-712 has a nice gauge that allows you to read it without a mobile device.   I would recommend Springers for the best prices in Brisbane.

 

Great response @Huxstang, I understand a little about electrics and solar, but I need another drink

[Hweebe]

18 hours ago, Huxstang said:

Personally I would put a smart shunt in so I could see the variables and actually understand what is happening before I charged batteries or solar panels.  Once you can see just how much you use and how much you generate you can make a much more informed decision.

Great advice...this is the first step. Getting more infomation will help inform next steps

 

[Junky]

Is this only happening at night, or is this when it's noticed? 

 

Have you swapped over the power supplies to each fridge, checking to see that the same power supply is failing, or the same fridge is failing?

 

Have you thoroughly checked all the connections between the fridges and the batteries?

 

Sounds to me like a poor connection. 

 

Disclaimer.... This is assuming your batteries are in top order, your engine is putting out approx 14v when underway, and your solar is connected up correctly with an anchor light and some lights music to calm the night.

 

There are no sound systems cranking out Metallica till all hours, television, stern lights on and the deck flood lights ablaze.  

 

 

 

 

 

 

[Junky]

Also keep in mind that a crook battery can kill a good battery in a parallel setup. 

[Old Scaley]

Some great info here @Huxstang @Hweebe and @Junky  Batteries always seemed to me to be such a simple thing - until you start to use them for things other than starting the car. I am always looking to learn more about battery choice and care, so thanks boys. 

[Huxstang]

Yes hopefully its useful for other people.  Not sure what happened to the original poster, maybe my post scared hi away - lol.

Like I said, my knowledge is all based on experience travelling and living off grid for long periods where keeping food and beer/wine cold is a massive priority.  And all before the advent of lithium and affordable solar.  We have had and solved more than our fair share of problems with electrics travelling the country and yet to have to resort to hot beer so doing something right.  

There are cheaper options if you want to wire in the ebay watt meter (listed as 200amp watt meter)…I still use similar on my solar blanket when charging the 4wd drinks fridge battery.  Lot cheaper than when I bought mine over 10 years ago but its still going.  At a glance tells you how much the solar panel is putting out and at the end of the day how much its generated.  Can put it inline with a fridge to see how much it consumes as well.  Pretty good value for @ $24.

 

 

[Hweebe]

On 15/01/2024 at 3:57 PM, Junky said:

Also keep in mind that a crook battery can kill a good battery in a parallel setup. 

This is always my worry as well, so whilst my dual battery setup can be run in parallel, I usually only use Battery 1 or Battery 2 isolated from each other and don't really run them in parallel at all.

[Huxstang]

10 hours ago, Hweebe said:

This is always my worry as well, so whilst my dual battery setup can be run in parallel, I usually only use Battery 1 or Battery 2 isolated from each other and don't really run them in parallel at all.

Have you thought about connecting them through a VSR?  I think Victron call them just a battery joiner but essentially they are the same…a voltage sensing relay.  They seperate the batteries under certain conditions and join them under set conditions.  IE join when voltage on the alternator charged battery reaches preset voltage (usually @ 13.4v) and separate when it hits the low voltage setting (@13.2v from memory).  Sort of guarantees you can run them as a joined pair without fear of flattening both.  The best part of them is that you can connect a charger to the secondary battery and it works in reverse….once that battery hits voltage it opens circuit through to the other battery.  Hope this makes sense.  Pretty much what any 4WD dual battery setup looks like.

Look up Victron Cyrix-ct

 

[Hweebe]

Good one @Huxstang I wired up a VSR on my 4wd starter / aux battery setup so I'm familiar with them.

I'm not sure why I didn't think of this as an option for the boat as well.  

[MattInOz]

On 14/01/2024 at 8:20 AM, RayM said:

Hi There,

i have 3 x 150ah lead batteries on my boat. 1 for Cranking and 2 for House use.

i run two small fridges off the house batteries (60L each) with a 160w solar panel.

One fridge will stay on all night but the other will turn off and on intermittently.

Do I need a larger solar panel like 500w ?

or do i need to keep my lead acid cranking battery and change the two house batteries to deep cycle ?

Any advice will be much appreciated.

 

Kind Regards,

Ray

The answer to your question is another two questions: Are the batteries charging to 100% during the day, and are they discharging to below a usable voltage with normal use overnight? A volt meter will answer the question for you... a lead acid battery at full charge will read just under 14 volts, and once below about 11 volts it'll probably be too discharged for your fridge. If your batteries are not charging completely you need a bigger solar panel, and if they're charging to 100% during the day and discharging too quickly at night you need bigger batteries (or possibly just new ones, get them load tested).

Of course, putting bigger batteries in might also require bigger solar panels to charge them too... have to suck it and see. If your current batteries are already at 100% by say 11am you can probably afford to put a bigger battery on it but if they struggle to get to 100% by say 4pm a bigger battery will require a bigger panel.

As for the type of battery, a deep cycle battery is specifically designed to be fully discharged and charged repeatedly, while a cranking battery is designed for the heavy, brief load of a starter motor and then immediately recharged by the alternator. If replacing your house batteries you want deep cycle (or dual use) ones ideally.