battery charge voltage

[Nickcf]

My 24v battery system (2x12v lead acid wet cell batteries and a Newmar computer controlled charger) shows over 29.5v when on charge. I always thought that more like 28v was the normal voltage.
Does this seem correct?

 

[mainshiptom]

What does the voltage drop to when chager is switched off?

What age are the battries?

 

[brianrunyard]

What are you using to measure the 29.5v, how accurate is it?

 

[Nickcf]

Haven't checked with a precision meter but the on board voltmeter and a portable one are probably within about 0.5 v (with the portable one reading a bit lower, so just over 29v). The on board voltmeters aren't graduated sufficiently to be able to read them to less than +/- 0.5v accuracy in reality.

Next time I'm on the boat I'll dig out the old trusty AVO mk8 and get some better readings.

With the charger off, the voltage drops to about 26v on modest load. I think the batteries must be the originals (4 years old) but I not had any problems with them losing charge or not delivering adequate current (both the auxilliary and engine start batteries)

nick

 

[Stoaty]

29.5V will give a 100% charge to your batteries assuming they are in good condition with a very small amount of gassing. 29.5V is about the maximum you would want to charge at. 27.6V would give an 80% charge and no gassing. All assuming your charger is intelligent in some way.

 

[Nickcf]

Stoaty,

thanks, yes it a newmar three phase unit although don't know much more than that (I know it has a temp sensor attached to one of the batteries though).

nick

 

[brianrunyard]

Assuming isn't reading low and that the voltage is between 29v and 29.5v, I'd say it's about right for a full charge.
As a 12v system would show a max of approx 14.6v.
I'd expect a 24v system to show approx 29.2v, so I'd be happy with your 29.5v provided the batteries aren't gassing.

 

[Stoaty]

[ QUOTE ]
Stoaty,

thanks, yes it a newmar three phase unit although don't know much more than that (I know it has a temp sensor attached to one of the batteries though).

nick

[/ QUOTE ]

Well it seems to me it's doing it's job well. Just keep an eye on the electrolyte level. If your losing a lot of electrolyte it is indicative of a battery or charger problem.

 

[Nickcf]

Stoaty,

In fact I do lose a lot of elctrolyte. When I bought the boat (not new) last Jan the cells needed a lot of water to top them up (probably half a litre per battery). I assumed just poor maintenance by the previous owners boatyard? The batteries seem to have plenty of power though. However checked again yesterday and had to top up again with about a quarter litre per battery which will be the third time this year. Battery voltage under charge (at absorption charge state according to the charger manual) was 29.4v. On the front of the charger it implies that the absorption voltage should be 28.5v? Is it likely the batteries are causing this or could the charger be cooking them?
The charger is a Newmar Phase Three model PT-24-45F.

When the alternators are charging the batteries the voltage reading is about 28.5v. The only battery which doesn't need topping up is the generator one which isn't connected to the charger! (same type and age as all the others Nov 2001).
There is a temperature compensator fitted to one of the batteries. Wonder if it would be worth removing that as the manual says that the output voltage is lower without it?

The charger is not left connected unless the boat is in use.

thnks

nick