Battery setup recommendation for short term cruising

[Richard10002]

12 hours ago, Col_T said:

 

I have always thought that it was tail current at 14.6v to determine when the batteries are fully charged - have I got that wrong as well?!

 

You're not wrong. I have always thought it was 14.4V, Tony uses 14.2V or above.

 

Some people use a tail current of 2%, some use 1%.

 

So it looks like a grey area where, as long as you are in the right ball park, you are doing the right thing.

 

If I understand things correctly, if you reach your stable tail current at 14.6V, your batteries will be a bit "fuller" than if you reach it at 14.4V or 14.2V.

[Tony Brooks]

4 minutes ago, Richard10002 said:

 

You're not wrong. I have always thought it was 14.4V, Tony uses 14.2V or above.

 

Some people use a tail current of 2%, some use 1%.

 

So it looks like a grey area where, as long as you are in the right ball park, you are doing the rig t thing.

 

If I understand things correctly, if you reach your stable tail current at 14.6V, your batteries will be a bit "fuller" than if you reach it at 14.4V or 14.2V.

 

Absolutely correct. It is all just a guide to how to do the best you can for your batteries. If a boater has an old 10/11 AC system as set by the factory then it would be regulating at 13.8 to 14.2 volts and would never go any higher, so it would be of no use to the boater to say dogmatically 14.x volts. I suspect the OP's B2B will give an absorption voltage of around (not looked it up) 14.6 to 14.8 volts, so again it means you can't be too specific over the voltage for this purpose.

 

I suppose even better is to say keep charging until the current has stopped dropping over an hour or so but the OP has  B2B and I think those drop into float voltage and as soon as they do the current is likely to stop dropping. The same applies to many solar controllers and battery chargers

[ditchcrawler]

On 05/10/2021 at 22:47, Col_T said:

 

I have always thought that it was tail current at 14.6v to determine when the batteries are fully charged - have I got that wrong as well?!

He did say PLUS not all alternators will reach that. I get to 14.5 volts on a good day

[cuthound]

On 06/10/2021 at 11:54, Tony Brooks said:

 

Absolutely correct. It is all just a guide to how to do the best you can for your batteries. If a boater has an old 10/11 AC system as set by the factory then it would be regulating at 13.8 to 14.2 volts and would never go any higher, so it would be of no use to the boater to say dogmatically 14.x volts. I suspect the OP's B2B will give an absorption voltage of around (not looked it up) 14.6 to 14.8 volts, so again it means you can't be too specific over the voltage for this purpose.

 

I suppose even better is to say keep charging until the current has stopped dropping over an hour or so but the OP has  B2B and I think those drop into float voltage and as soon as they do the current is likely to stop dropping. The same applies to many solar controllers and battery chargers

 

When BT used to have large open wet cell lead acid batteries (up until about 1980), end of charge was decided when the tail current had been constant over 3 X 30 minute readings at a cell voltage of 2.66 volts per cell.

 

However the battery is 99.9% charged when the tail current is down to 1%  and the battery is above 2.4 volts per cell.

 

As always it is a balance between getting the last bit of charge in and the time you are prepared to do this for.

Edited October 8, 2021 by cuthound
Premature posting

[Tony Brooks]

3 minutes ago, cuthound said:

 

When BT used to have large open wetcwll.lead acid batteries (up until about 1980), end of charge was decided when the tail current had been constant over 3 X 30 minute readings at a cell voltage of 2.66 volts per cell. 

 

That sounds very much like equalising and I suspect would not be done every day. I also think that you may have missed the bit about topping up as required and monitoring the temperature during the process. As MtB said, lead acid batteries are never totally and fully charged. Your process would convert  a bit more sulphate than equalising at 15.5V and get them a bit more fully charged.

 

I think it would be damaging to use that voltage every day or even once a week and would definitely destroy many types of sealed batteries.

[cuthound]

Just now, Tony Brooks said:

 

That sounds very much like equalising and I suspect would not be done every day. I also think that you may have missed the bit about topping up as required and monitoring the temperature during the process. As MtB said, lead acid batteries are never totally and fully charged. Your process would convert  a bit more sulphate than equalising at 15.5V and get them a bit more fully charged.

 

I think it would be damaging to use that voltage every day or even once a week and would definitely destroy many types of sealed batteries.

 

You are correct that 2.66 volts is also used for equalising, and in BT was done quarterly. However the technical instructions clearly stated that a battery was not 100% charged until that voltage had been achieved and the tail current constant for 3 X 30 minutes 

 

A weekly refresher charge was done and terminated when the tail current was down to 2%, at which point the battery voltage was around 2.4 volts per cell. However the battery at that point was almost but not fully charged.

 

Temperature corrected specific gravity readings were taken periodically through charging process. Tipping up was done with deionised water and a 2 gallon bucket.

 

I have posted photos of the large open cells before, but they had a life of 25 years despite being fully discharged every 2 years (conditioning cycle) to assess capacity.

[Tony Brooks]

11 minutes ago, cuthound said:

 

You are correct that 2.66 volts is also used for equalising, and in BT was done quarterly. However the technical instructions clearly stated that a battery was not 100% charged until that voltage had been achieved and the tail current constant for 3 X 30 minutes 

 

A weekly refresher charge was done and terminated when the tail current was down to 2%, at which point the battery voltage was around 2.4 volts per cell. However the battery at that point was almost but not fully charged.

 

Temperature corrected specific gravity readings were taken periodically through charging process. Tipping up was done with deionised water and a 2 gallon bucket.

 

I have posted photos of the large open cells before, but they had a life of 25 years despite being fully discharged every 2 years (conditioning cycle) to assess capacity.

 

I agree with all that, but must point out that you had the equipment and facilities to it. The average boater does not, so any advice has to recognise that. It is a case of doing the best you can with what you have. If anyone is still running a 13.8 to 14.2V regulated 10 or 11AC charging set up they will always suffer more sulphation  than someone  running a 14.4V alternator and will also never be able to get their batteries as fully charged.