Battery chargers and two batteries in the bank

[dolabriform]

Hi all

Another power related question... I'm trying to get my head around something probably very simple.

I have two identical 75AH leisure batteries on the boat, alternator charged with a 1 / 2/ 1+2 switch.

I have a 100 W solar panel that I'm going to install, with a solar charge controller designed for 2 batteries.

I'd also like to add shore power to the boat, and to this end would want to be able to charge / maintain the batteries whilst connected. Would a single charger such as this suffice:

https://www.foxschandlery.com/ctek-mxs-5-0-test-and-charge-intelligent-battery-charger

Or would I need a charger for each battery?

Is the solar charger going to cause a problem with the alternator and shore power chargers by creating a false battery reading as it will be ( ideally ) be putting voltage into the circuit?

Thanks

David

 

[PaulRainbow]

Hi all

Another power related question... I'm trying to get my head around something probably very simple.

I have two identical 75AH leisure batteries on the boat, alternator charged with a 1 / 2/ 1+2 switch.

Erm..... OK, i won't mention the 1-2-B switch :disgust:

I have a 100 W solar panel that I'm going to install, with a solar charge controller designed for 2 batteries.

Ok, no problem there.

I'd also like to add shore power to the boat, and to this end would want to be able to charge / maintain the batteries whilst connected. Would a single charger such as this suffice:

https://www.foxschandlery.com/ctek-mxs-5-0-test-and-charge-intelligent-battery-charger

Or would I need a charger for each battery?

You don't need two chargers. The solar panel will keep the batteries charged when you are away from the boat, so you need to consider why you want to fit shore power and a mains charger, be good to share that thinking with us too

As you don't need it to keep the batteries charged when you are not onboard, i assume you might want it to keep the batteries charged up when you are onboard and the solar panel isn't keeping up (presumably if you are sitting in the marina in the evening and using power). If that's the case the one you linked to is not really big enough, unless you only want a couple of low power lights on.

For similar money you could have twice the output : https://www.batterymegastore.co.uk/...ron-energy-chargers/victron-bpc121030064.html

For a teeny bit more, three times the output : https://www.batterymegastore.co.uk/...ron-energy-chargers/victron-bpc121530064.html

Is the solar charger going to cause a problem with the alternator and shore power chargers by creating a false battery reading as it will be ( ideally ) be putting voltage into the circuit?

Effects vary, generally depending on the charging profiles of the various sources. What you will most likely find is that if the mains charger is on, the solar controller will go into float mode, not usually a problem as you don't turn the charger on until the evening.

 

[dolabriform]

Thanks for your quick response Paul, much appreciated.

Erm..... OK, i won't mention the 1-2-B switch :disgust:
Yes, I know they are frowned upon, and it's on the todo list

Ok, no problem there.

You don't need two chargers. The solar panel will keep the batteries charged when you are away from the boat, so you need to consider why you want to fit shore power and a mains charger, be good to share that thinking with us too

As you don't need it to keep the batteries charged when you are not onboard, i assume you might want it to keep the batteries charged up when you are onboard and the solar panel isn't keeping up (presumably if you are sitting in the marina in the evening and using power). If that's the case the one you linked to is not really big enough, unless you only want a couple of low power lights on.

For similar money you could have twice the output : https://www.batterymegastore.co.uk/...ron-energy-chargers/victron-bpc121030064.html

For a teeny bit more, three times the output : https://www.batterymegastore.co.uk/...ron-energy-chargers/victron-bpc121530064.html

Effects vary, generally depending on the charging profiles of the various sources. What you will most likely find is that if the mains charger is on, the solar controller will go into float mode, not usually a problem as you don't turn the charger on until the evening.

re the 1/2 switch... it's on the list :ambivalence:

Maybe I'm being paranoid. We have a small powered cool box
https://www.dometic.com/en-gb/uk/pr...etic-tropicool-tcx-21-_-153289#specifications
Which I'd like to keep on when we are sailing to keep the milk etc cool ( especially for the kids bottles ), and also powering electronics etc.

I'm concerned that in a scenario where we are sailing for 10 hours, and the engine is only switched on for 1/2 an hour or so to get us in and out of a marina that we won't get enough charge out of the engine and solar. Or if we have anchored for a couple of days and visit a marina for a top up.

Thanks for the link to the victron kit, looks much better!

 

[PaulRainbow]

Thanks for your quick response Paul, much appreciated.



re the 1/2 switch... it's on the list :ambivalence:

Maybe I'm being paranoid. We have a small powered cool box
https://www.dometic.com/en-gb/uk/pr...etic-tropicool-tcx-21-_-153289#specifications
Which I'd like to keep on when we are sailing to keep the milk etc cool ( especially for the kids bottles ), and also powering electronics etc.

I'm concerned that in a scenario where we are sailing for 10 hours, and the engine is only switched on for 1/2 an hour or so to get us in and out of a marina that we won't get enough charge out of the engine and solar. Or if we have anchored for a couple of days and visit a marina for a top up.

Thanks for the link to the victron kit, looks much better!

The solar panel will help a lot, especially in this weather. Given the above i'd definitely go for one of the Victron chargers, for the little extra the 15a makes sense.

 

[BabaYaga]

If you want to run a cool box, I would suggest that your top priority should be to get at least one other 75Ah battery, connected in parallel with one of the two already in place. So that you will have a house bank of 150Ah, while the third battery is reserved for engine starting only.
Unless you have frequent starting difficulties, connecting solar or shore power to the battery used for starting has no benefit, provided that you remember to operate the switch correctly.

 

[PaulRainbow]

If you want to run a cool box, I would suggest that your top priority should be to get at least one other 75Ah battery, connected in parallel with one of the two already in place. So that you will have a house bank of 150Ah, while the third battery is reserved for engine starting only.
Unless you have frequent starting difficulties, connecting solar or shore power to the battery used for starting has no benefit, provided that you remember to operate the switch correctly.

It does if you leave the boat for long periods, besides, there is no downside to keeping the engine battery charged up.

 

[William_H]

By "coolbox" I presume you mean one of those peltier type coolers. (capable of heating or cooling with a switch) They are terrible as using a lot of current for not much cooling. Suggest you look at something like WACO CF18 compressor fridge that will work as a freezer if you want. Tend to draw about 3 amps with a 30% duty cycle. So average about 1 amp. Depending on temp selected and ambient temp. It should be possible to sustain that fridge on the solar panel. ol'will

 

[dolabriform]

By "coolbox" I presume you mean one of those peltier type coolers. (capable of heating or cooling with a switch) They are terrible as using a lot of current for not much cooling. Suggest you look at something like WACO CF18 compressor fridge that will work as a freezer if you want. Tend to draw about 3 amps with a 30% duty cycle. So average about 1 amp. Depending on temp selected and ambient temp. It should be possible to sustain that fridge on the solar panel. ol'will

Hi Will

Yes, it is one of the cheaper ones, but like everything it all comes down to cost. I'd love to upgrade ( maybe in the future ) but at the moment I'm stuck with this one. Altho it's a bit noisy, it does seem to work quite well.

Regards

David

 

[BabaYaga]

there is no downside to keeping the engine battery charged up.

Depends on at which voltage. Exposing an already fully charged unloaded battery to absorption voltages for extended periods might shorten its life, in my opinion.
But that another thread (which we have already had, I believe).

 

[PaulRainbow]

Depends on at which voltage. Exposing an already fully charged unloaded battery to absorption voltages for extended periods might shorten its life, in my opinion.
But that another thread (which we have already had, I believe).

I believe we have

In my professional experience i have yet to see any evidence of this at all.

May i ask, what experience/knowledge do you draw on to form your opinion ?

 

[Graham376]

Battery chargers can be had cheaper from caravan shops and battery suppliers, than so called "marine" suppliers. Typical is this 3 stage 20 amp one from 12 volt Planet for open lead acid, which can also be used as a power supply. https://www.12voltplanet.co.uk/rovert-automatic-multi-stage-leisure-battery-charger-12v-20a.html

 

[BabaYaga]

I believe we have

In my professional experience i have yet to see any evidence of this at all.

May i ask, what experience/knowledge do you draw on to form your opinion ?

With all due respect for your professional expertise, I thought it was well established knowledge that batteries, especially of the sealed type, should not be held at absorption voltage for extended periods, as this will dry them out and shorten their life?
If this was not the case, why would those who make shore power chargers bother with float voltages?

Some more interesting questions with less obvious answers: What constitutes an 'extended period' in this respect? What is the accumulated effect on the already charged starter battery connected by VSR of repeatedly charging up heavily depleted house batteries on shore power?

I am not saying harm WILL be done, I say might be. Therefore I advocate caution: Don't set up your charging system so that it automatically tries to charge up a battery that is already full, if the benefit of doing so is small or non existent.

You have not seen any evidence. If a starter battery in one of your customers' boats dies after 5 years, instead of 8 or 10 – how much time do you devote to establish the cause?

 

[PaulRainbow]

You have not seen any evidence. If a starter battery in one of your customers' boats dies after 5 years, instead of 8 or 10 – how much time do you devote to establish the cause?

Short of time for a more detailed reply at present, will get back to your other comments.

Just to say, i recently had to look into some battery issues with a customers boat. The bow thruster batter is 3 years old, the engine and starter batteries are of unknown vintage as they were on the boat when the current owner bought the boat, so they will be several years old. The domestic and engine batteries were being charged by a split charge relay, with an advanced regulator to keep the voltages up, plus a Sterling shore power charger which charged all batteries on the same profile. Both domestic batteries were failing to hold a decent charge but the engine battery is working very well.

 

[William_H]

Hi Will

Yes, it is one of the cheaper ones, but like everything it all comes down to cost. I'd love to upgrade ( maybe in the future ) but at the moment I'm stuck with this one. Altho it's a bit noisy, it does seem to work quite well.

Regards

David

The other alternative is the use of frozen water from home freezer. In a well insulated box it can last for quite a few days. Anything to allow you to turn of that cool box. So solving battery and charging problems. ol'will

 

[dolabriform]

The other alternative is the use of frozen water from home freezer. In a well insulated box it can last for quite a few days. Anything to allow you to turn of that cool box. So solving battery and charging problems. ol'will

Thanks Will, good idea. We do have 'freeze blocks' which we use in a normal cool box, I hadn't thought of using those in the cooler as well!

 

[KellysEye]

>As you don't need it to keep the batteries charged when you are not onboard

Flat battries cannot be recharched and there is no solar power in the winter when the boat is usually left.

 

[PaulRainbow]

>As you don't need it to keep the batteries charged when you are not onboard

Flat battries cannot be recharched and there is no solar power in the winter when the boat is usually left.

yawn