Cant get 14.8v from my charger - what to do

[affinite]

I have a fairly large battery installation comprising 3 banks;
520Ahr House bank - Flooded Lead Acid
100Ahr Start Battery - Sealed Lead Acid
200Ahr Thruster Bank - Sealed Lead Acid

The charging arrangements for my batteries is very under-specced so Im upgrading the solar panel and charger to 350W /30A next season
I'll live with the alternator as-is (60A with Sterling A-B charger)
This query relates to the mains charging

The existing charger is rated at 25Amps (3 outputs)
Its highest Absorption voltage setting is 14.4v

The Trojan house bank wants 14.8v absorption voltage but rather than replace the complete charger Im wondering about buying the Sterling Battery Chemistry Battery Charging module which can "boost" charging voltage to 14.8v (Apparently this device will allow me to leave the other 2 banks charging at 14.4v but the house will get 14.8v)
Has anyone used one of these devices? - Id be interested in feedback
OK so I can maybe fix the low charging voltage but Is my existing 25A max charge current a problem ?
Im aware of the advice that the charger should be rated at 10-13% of C20 ie 52-67Amps but will charging at max 25A actually damage the batteries or will it just take longer to get to full charge ?
(I can probably live with a slower mains charge time as the solar will run the boat during the day)
Thanks

 

[halcyon]

I have a fairly large battery installation comprising 3 banks;
520Ahr House bank - Flooded Lead Acid
100Ahr Start Battery - Sealed Lead Acid
200Ahr Thruster Bank - Sealed Lead Acid

The charging arrangements for my batteries is very under-specced so Im upgrading the solar panel and charger to 350W /30A next season
I'll live with the alternator as-is (60A with Sterling A-B charger)
This query relates to the mains charging

The existing charger is rated at 25Amps (3 outputs)
Its highest Absorption voltage setting is 14.4v

The Trojan house bank wants 14.8v absorption voltage but rather than replace the complete charger Im wondering about buying the Sterling Battery Chemistry Battery Charging module which can "boost" charging voltage to 14.8v (Apparently this device will allow me to leave the other 2 banks charging at 14.4v but the house will get 14.8v)
Has anyone used one of these devices? - Id be interested in feedback
OK so I can maybe fix the low charging voltage but Is my existing 25A max charge current a problem ?
Im aware of the advice that the charger should be rated at 10-13% of C20 ie 52-67Amps but will charging at max 25A actually damage the batteries or will it just take longer to get to full charge ?
(I can probably live with a slower mains charge time as the solar will run the boat during the day)
Thanks

Current is not the problem. 10 -13% is a nominal best not max, it will just take longer to charge.

Problem is 14.4v was a voltage for transformer chargers, 14.8v is switched mode voltage to get around charge profile problem.

Brian

 

[TernVI]

Trojan's charging profile is based around bulk charging at 10 to 13% of the C(20) capacity.
If your charger can only do 5%, you're not using their profile, so you probably want a different absorption voltage anyway.
The Trojan profile is built around applications which need to charge from a deep cycle in a short time.
If you want to do that, you will need a more powerful charger.
If you don't want or need to do that, a smarter charger with a better charging algorithm might be better.

With your low current limit, the battery will be at a higher state of charge when the terminal volts hit 14.8, It 's a different profile completely. You are taking the battery to a different combination of V and SOC where it may gas more.

 

[PaulRainbow]

25a is very under spec', i'd fit a decent 50a charger, at least.

 

[affinite]

25a is very under spec', i'd fit a decent 50a charger, at least.

Its just the original charger I think; fitted long before I bought the boat and probably when the house bank was 100Ahr
I agree that its now underspeced according to perceived wisdom (10% of bank C20) but can you explain why a big charger is necessary?
Wont the 25A charger just charge 50% slower ?
Thanks again

 

[pvb]

Its just the original charger I think; fitted long before I bought the boat and probably when the house bank was 100Ahr
I agree that its now underspeced according to perceived wisdom (10% of bank C20) but can you explain why a big charger is necessary?
Wont the 5A charger just charge 50% slower ?
Thanks again

A smaller charger will charge more slowly, but it'll still charge.

But if its maximum voltage is 14.4v, you'll never get the batteries to 14.8v unless it's with the alternator and the A-to-B charger.

 

[TernVI]

A smaller charger will charge more slowly, but it'll still charge.

But if its maximum voltage is 14.4v, you'll never get the batteries to 14.8v unless it's with the alternator and the A-to-B charger.

But you don't want to get the batteries to 14.8V. You want them to get to 100% charged, which is not the same thing at all.
14.8V is one means to that end, the kind of charging profile from various charger manufacturers are different means to the same end, albeit generally slower.

 

[PaulRainbow]

Its just the original charger I think; fitted long before I bought the boat and probably when the house bank was 100Ahr
I agree that its now underspeced according to perceived wisdom (10% of bank C20) but can you explain why a big charger is necessary?
Wont the 5A charger just charge 50% slower ?
Thanks again

As others have said, you do need to get the voltage up, but then you are more or less correct, 25a charger will just be slower then a 50a one. Won't take twice as long, the 50a charger won't put 50a out for the full duration of charging the batteries up. If you have to change the charger anyway, may as well fit bigger. I'd normally suggest a Victron charger, but over 30a they get pricey, so as a compromise (if you want to spend less) perhaps look at the Sterling Pro Charge Ultra 40a.

 

[affinite]

Thanks for the advice.
The fog is clearing but ;
I'm still not 100% clear on how battery charging profiles and battery charger operation relate to each other so I need to do further research at the battery university !

 

[Mistroma]

Thanks for the advice.
The fog is clearing but ;
I'm still not 100% clear on how battery charging profiles and battery charger operation relate to each other so I need to do further research at the battery university !

The standard Cristec charger on my Jeanneau doesn't have a suitable setting either. However, I don't connect to shorepower much and the Cristec is mostly used at anchor outside peak summer months. The model I have has a potentiometer to adjust the settings and it was pretty simply to set that to give 14.8V. It is a pretty basic charger and altering this brings up the float voltage as well, 14.2V if I remember correctly. It works well for me because I don't run the generator for many hours and it is usually turned off by the time the voltage drops to 14.2V. Solar takes over for the rest of the day and will hold a proper float voltage if there's enough sun.

Adjusting the potentiometer changes all the settings but it is in a predictable manner. I switch to another setting if on shorepower at a quay for several days and float is OK at 13.4V even though it only gives 14.0V when boost is on. That's close enough as solar charges to 100% and mains simply stops overnight discharge when on shore power.

I have a 40A charger with 450Ah domestic (+start & bowthruster which are obviously fully charged).

 

[pvb]

But you don't want to get the batteries to 14.8V. You want them to get to 100% charged, which is not the same thing at all.
14.8V is one means to that end, the kind of charging profile from various charger manufacturers are different means to the same end, albeit generally slower.

Did you notice in the OP it said "The Trojan house bank wants 14.8v absorption voltage..."