Battery charger advice

[gordon029]

Evening all. I have just changed my boat and the new to me boat has no built in battery charger. I had a mobitronic type on the last boat so want to find something similiar which I can fit and forget knowing that the shore power will keep the batteries charged up for when I need them.I have been looking on line but cant seem to find a relatively simple one . So I would appreciate some advice as to whats available thats reasonably priced and not too complicated to fit. I am also looking to fit a circuit breaker to cover the shorepower sockets I will be fitting so again advice would be appreciated as to where I can get one of these. Thank you for reading and thank you in advance for the assistance

 

[VicS]

Evening all. I have just changed my boat and the new to me boat has no built in battery charger. I had a mobitronic type on the last boat so want to find something similiar which I can fit and forget knowing that the shore power will keep the batteries charged up for when I need them.I have been looking on line but cant seem to find a relatively simple one . So I would appreciate some advice as to whats available thats reasonably priced and not too complicated to fit. I am also looking to fit a circuit breaker to cover the shorepower sockets I will be fitting so again advice would be appreciated as to where I can get one of these. Thank you for reading and thank you in advance for the assistance

Your incoming shorepower supply should incorporate an RCD, and mcbs for each circuit in the boat.

A garage consumer unit is a convenient and inexpensive way of providing this protection to the a shorepower system. They usually incorporate a suitable RCD and a couple of mcbs, one rated at 16 amps, which can be used to supply a small number of sockets, and one at 6 amps, which can be used for supplying a battery charger.

You presumably plan to leave your boat with the shorepower connected therefore a galvanic isolator will be an essential item to fit.

Cannot advise on the choice of charger but others no doubt will although it might help if they know the sort of size ( amps output) charger you need and also how many battery banks you will need to charge simultaneously.

 

[gordon029]

Thank you for your reply. That's the kind of information I was hoping for. I had been looking at household systems and that seems to fit the plan. Now as to the charging system are mobitronic no longer available or superceded by some other system? Thanks again

 

[PaulRainbow]

You presumably plan to leave your boat with the shorepower connected therefore a galvanic isolator will be an essential item to fit.

Only if he bonds the shore power ground to the DC negative, otherwise there is no point.

 

[PaulRainbow]

I'd look at a Victron charger.

 

[jiris]

Evening all. I have just changed my boat and the new to me boat has no built in battery charger. I had a mobitronic type on the last boat so want to find something similiar which I can fit and forget knowing that the shore power will keep the batteries charged up for when I need them.I have been looking on line but cant seem to find a relatively simple one . So I would appreciate some advice as to whats available thats reasonably priced and not too complicated to fit. I am also looking to fit a circuit breaker to cover the shorepower sockets I will be fitting so again advice would be appreciated as to where I can get one of these. Thank you for reading and thank you in advance for the assistance

I have been using this charger for about 2 years now:
https://www.ebay.com.au/itm/NEW-12V...228173?hash=item53fa37854d:g:9PoAAOSwmSdaZ-We

By performance, ease of use and price it is hard to beat.

 

[ghostlymoron]

6a is a bit low for a charger.

Your incoming shorepower supply should incorporate an RCD, and mcbs for each circuit in the boat.

A garage consumer unit is a convenient and inexpensive way of providing this protection to the a shorepower system. They usually incorporate a suitable RCD and a couple of mcbs, one rated at 16 amps, which can be used to supply a small number of sockets, and one at 6 amps, which can be used for supplying a battery charger.

You presumably plan to leave your boat with the shorepower connected therefore a galvanic isolator will be an essential item to fit.

Cannot advise on the choice of charger but others no doubt will although it might help if they know the sort of size ( amps output) charger you need and also how many battery banks you will need to charge simultaneously.

 

[ghostlymoron]

It's really difficult to suggest a charger when you've not said what batteries you have. C-Tek are often recommended.

 

[BabaYaga]

6a is a bit low for a charger.

Although, the 6A refers to 240v AC.
From a 12v DC perspective that equals 120A, which should leave capacity for all but the largest chargers.
For example, my 12v 25A charger has a stated power draw of 2.9A maximum.

 

[KREW2]

By one that gets your batteries up to full charge.

I have a 3 stage Hawk battery charger built in and was always pleased with it, until I fitted a Merlin Smartguage battery monitor, and it would only show 70% state of charge after being left on for a week.
I emailed Merlin and found them very helpful, they directed me to this FAQ, page, http://www.smartgauge.co.uk/sga_faq.html which tries to explain the complexity of batteries, and how best to charge them.
Click on the question "Why doesn't SmartGauge ever reach 100% charge status?" and it will tell you what you need to know about battery charging.
I took their advice, I disconnected the Hawk, and used a more powerful charger from home. After 4 hours I had a reading of 15.8 volts at the battery posts, after 10 hours I had 100% charge.
The FAQ on "SG and State of Charge" is interesting. http://www.smartgauge.co.uk/sg_soc.html the answer is a bit long winded, skip the first half and pick it up half way down the page, it gives a good understanding of how to look after, and get the best out of your batteries.

 

[robbieg]

Ctek M300 is a very good marine charger-easy to fit, temperature regulates and you can leave it to get on with its job. Works for lead acid sealed AGM etc. Link here https://www.foxschandlery.com/ctek-...MIhtHrid712QIVrLDtCh0MuAS8EAUYAiABEgJuFfD_BwE

One listed on the For Sale Forum (self interest declaration-listed by me!)

 

[PaulRainbow]

Although, the 6A refers to 240v AC.
From a 12v DC perspective that equals 120A, which should leave capacity for all but the largest chargers.
For example, my 12v 25A charger has a stated power draw of 2.9A maximum.

Using your calculation above, a 30a charger would only need a 1.5a fuse, that's clearly not correct. You can't work the amps out like that. For instance, a 30a Sterling charger will need an 11a fuse, according to Sterling (although mine is happy with a 10a MCB).

It will vary, depending on the charger, a 6a MCB would be ok for a small charger (up to about 10a), anything over that might be pushing it. Not a big deal to swap an MCB though.

A bigger concern for me would be using a 16a breaker for the sockets, on a boat with a 16a supply.

 

[jac]

Using your calculation above, a 30a charger would only need a 1.5a fuse, that's clearly not correct. You can't work the amps out like that. For instance, a 30a Sterling charger will need an 11a fuse, according to Sterling (although mine is happy with a 10a MCB).

It will vary, depending on the charger, a 6a MCB would be ok for a small charger (up to about 10a), anything over that might be pushing it. Not a big deal to swap an MCB though.

A bigger concern for me would be using a 16a breaker for the sockets, on a boat with a 16a supply.

Is there confusion between the 240v input (and associated fuse) and the 12v nominal output and associated fuse.

The 12 v output at 20 amps will only draw 1 amp at 240 v (assuming no inefficiency) given that they are massively inefficient I would expect a 3a fuse for the input to be marginal. Given that the nominal 12v output is realistically more likely to get to 15v then you're looking at 300w of output. To make that 1kw of input (I.e 4amps) should be sufficient but as different models have different efficiencies, best to just follow the makers fuse size recommendations.

Key thing is to understand the amount of power that the charger is expected to output.. That is directly related to battery bank size. An electrician advised me to think along the lines of 10amps output for each 100ah of battery bank. The rationale being that I could expect to see discharge down to about 50% of capacity leaving 10 amps to replace 50ah. The first 30 is relatively easy to do and should be done in 3-4 hours. The remaining 20% will take a huge amount of time and the output will be quite low, not the nominal 10a per 100Ah suggested. . 10 hours with no discharge should be ok but given that most boats in use will still being drawing power (e.g. Lights and fridge) for practical purposes 95% would be maximum that I was likely to see.

Of course if the usage pattern is different and the charger is designed to recharge the batteries from Sunday evening till Friday evening thereby giving full capacity for the next weekend then a much lower output is ok. The bulk phase will be slower but if it takes 10'hours to recharge to 80% then it's hardly going to make any practical impact over the course of the working week on the end state of charge.

 

[PaulRainbow]

Is there confusion between the 240v input (and associated fuse) and the 12v nominal output and associated fuse.

The 12 v output at 20 amps will only draw 1 amp at 240 v (assuming no inefficiency) given that they are massively inefficient I would expect a 3a fuse for the input to be marginal. Given that the nominal 12v output is realistically more likely to get to 15v then you're looking at 300w of output. To make that 1kw of input (I.e 4amps) should be sufficient but as different models have different efficiencies, best to just follow the makers fuse size recommendations.

I think you're right, BabaYaga was just making the calculation without making any allowances. Following the makers recommendation is good advice.

Key thing is to understand the amount of power that the charger is expected to output.. That is directly related to battery bank size. An electrician advised me to think along the lines of 10amps output for each 100ah of battery bank. The rationale being that I could expect to see discharge down to about 50% of capacity leaving 10 amps to replace 50ah. The first 30 is relatively easy to do and should be done in 3-4 hours. The remaining 20% will take a huge amount of time and the output will be quite low, not the nominal 10a per 100Ah suggested. . 10 hours with no discharge should be ok but given that most boats in use will still being drawing power (e.g. Lights and fridge) for practical purposes 95% would be maximum that I was likely to see.

Of course if the usage pattern is different and the charger is designed to recharge the batteries from Sunday evening till Friday evening thereby giving full capacity for the next weekend then a much lower output is ok. The bulk phase will be slower but if it takes 10'hours to recharge to 80% then it's hardly going to make any practical impact over the course of the working week on the end state of charge.

Another consideration is the amount of power you will be using whilst trying to recharge the batteries. This is where fitting cheaper, under sized, chargers can cause problems. If the charger can't keep up with current demand, plus put some charge back into the batteries you're in trouble.

As you say, usage has its part to play, If you're day sailing then going home, a relatively low output charger would be fine. If you're cruising with some stops in marinas than a higher output charger would be a must.

 

[Richard10002]

By one that gets your batteries up to full charge.

I have a 3 stage Hawk battery charger built in and was always pleased with it, until I fitted a Merlin Smartguage battery monitor, and it would only show 70% state of charge after being left on for a week.
I emailed Merlin and found them very helpful, they directed me to this FAQ, page, http://www.smartgauge.co.uk/sga_faq.html which tries to explain the complexity of batteries, and how best to charge them.
Click on the question "Why doesn't SmartGauge ever reach 100% charge status?" and it will tell you what you need to know about battery charging.
I took their advice, I disconnected the Hawk, and used a more powerful charger from home. After 4 hours I had a reading of 15.8 volts at the battery posts, after 10 hours I had 100% charge.
The FAQ on "SG and State of Charge" is interesting. http://www.smartgauge.co.uk/sg_soc.html the answer is a bit long winded, skip the first half and pick it up half way down the page, it gives a good understanding of how to look after, and get the best out of your batteries.

My Smartgauge reads 100% long before the batteries are actually full, and I think the Smartgauge manual warns about this.

When my Smartgauge shows 100% the batteries are still drawing 15-20A, (NASA BM2 monitor), and they aren’t full until they are drawing as low as 2 or 3 Amps, which takes a few hours.

So.... in some/many cases, if you stop charging as soon as your Smartgauge shows 100% you will soon destroy your batteries. Having said that, if your batteries are left charging on shore power for hours, or days, after the Smartgauge shows 100%, the Smartgauge anomaly won’t matter.

I am off grid, so use a generator to charge, so it matters to me, and I learned the hard way.

 

[BabaYaga]

Is there confusion between the 240v input (and associated fuse) and the 12v nominal output and associated fuse.

The 12 v output at 20 amps will only draw 1 amp at 240 v (assuming no inefficiency) given that they are massively inefficient I would expect a 3a fuse for the input to be marginal. Given that the nominal 12v output is realistically more likely to get to 15v then you're looking at 300w of output. To make that 1kw of input (I.e 4amps) should be sufficient but as different models have different efficiencies, best to just follow the makers fuse size recommendations.

I think one often looks in vain for a figure of the AC current draw in charger specifications, so the inefficiency could be difficult to estimate. However, as I mentioned in my previous post, for my charger, a CTEK M300, this is stated as 2.9A maximum.
Assuming this is a representative number, it is possible to make a rough estimate: The maximum output of the charger, 25A at say 14,4v would require something like 1.5-1.6A, while the remaining 1.4-1.3A would be spent as heat loss, driving the fan etc. So an efficiency of just over 50 percent.
To me this suggests that one could likely power a 40A charger (40 x 14,4 / 240) x 2(for inefficiency) = 4.8 and still have some margin to the 6A MCB.

I think you're right, BabaYaga was just making the calculation without making any allowances. Following the makers recommendation is good advice.

Yes, that was a theoretical calculation, allowances are outlined above.
The maker recommendation you mention, 11A@240v fuse for a 30A charger @12v suggests to me that this charger is massively less efficent than the CTEK. It is not a charger/inverter by any chance?

 

[PaulRainbow]

Yes, that was a theoretical calculation, allowances are outlined above.
The maker recommendation you mention, 11A@240v fuse for a 30A charger @12v suggests to me that this charger is massively less efficent than the CTEK. It is not a charger/inverter by any chance?

Sorry, that should be 7a at 240v, i quoted the 110v figure.

 

[BabaYaga]

Sorry, that should be 7a at 240v, i quoted the 110v figure.

That indicates an efficiency of well under 30 percent for that charger.
Maybe this is a typical value (and the CTEK particularly good in this respect)?
If this is the case, a 6A mcb should still be able to support a charger of 20 or perhaps even 25A.

 

[PaulRainbow]

That indicates an efficiency of well under 30 percent for that charger.
Maybe this is a typical value (and the CTEK particularly good in this respect)?
If this is the case, a 6A mcb should still be able to support a charger of 20 or perhaps even 25A.

Not necessarily, that's just the fuse rating, you're assuming that the fuse is rated at the full load current, which it isn't. Full load current for the 30a Sterling charger is 2.3a, less than the 25a Ctek.

 

[matthewriches]

6 amp fuse at 230v AC probably good for about 70-80 amp charger at 12v DC.

That indicates an efficiency of well under 30 percent for that charger.
Maybe this is a typical value (and the CTEK particularly good in this respect)?
If this is the case, a 6A mcb should still be able to support a charger of 20 or perhaps even 25A.