Numax charger/ float/ equalise difference and expected behaviour

[Emonaboat]

Hi There

 

I have been searching through the archives regarding this and can't find a specific answer to my puzzle. We have a 30A numax charger and 2 batteries. We are on shore power only as no working engine. 12v used for 5 x 20w halogen capsule lights and one water pump just for kitchen sink (handy as we get fairly frequent mains power cuts).

 

I'm trying to find out how this charger should behave with healthy batteries, as I recently replaced the ones I inherited with the boat, believing them to be shot. The reason I thought they were shot is that the previous owner told us she only turned the charger on every few days "when the lights got a bit dim". We found that we were having to turn the charger on more frequently than that. I have since been told that these numax chargers are designed to be left on all the time and the way she had been using them had likely done for them. They were only 18 months old and were thick plate leisure batteries, 110ah. Once we found out that the charger should be left on we found that it would come on to equalise charging whenever lights or pump were being used, and only switch back to float charging once lights and pump were both off.

 

Then I got offered 2 brand new mercedes truck batteries for 100 quid, and they are maintenance free and only 100ah. They do not seem to have made any improvment and in fact are a little weaker.

 

So my questions are:

 

1. Is it normal that the numax is permanently on equalise charging (ie fan comes on) whenever any device powered by the batteries is on? And if so are there any alternatives that make less noise?

2. What is the difference between equalise and float charging and should I expect float charging to stop after a prolonged period of no device being used?

3. I have an inkling that there may well have been nothing wrong with the old batteries and that this is why the new ones appear to be weaker, as they are an inferior spec, and if both new and old are in good order, new would therefore appear weaker. How is it best to test this?

4. Does it even matter if the batteries are shot if we are permanently connected to shore? Will we be using more shore power with duff batteries or not?

 

Thanks a lot for looking

 

Dave on Newlyn

 

[nicknorman]

I think when you say "equalise" you perhaps mean bulk or absorption, or are you saying "equalise" for a good reason? Anyway, some answers in red below:

 

Hi There

 

I have been searching through the archives regarding this and can't find a specific answer to my puzzle. We have a 30A numax charger and 2 batteries. We are on shore power only as no working engine. 12v used for 5 x 20w halogen capsule lights and one water pump just for kitchen sink (handy as we get fairly frequent mains power cuts).

 

I'm trying to find out how this charger should behave with healthy batteries, as I recently replaced the ones I inherited with the boat, believing them to be shot. The reason I thought they were shot is that the previous owner told us she only turned the charger on every few days "when the lights got a bit dim". We found that we were having to turn the charger on more frequently than that. I have since been told that these numax chargers are designed to be left on all the time and the way she had been using them had likely done for them. They were only 18 months old and were thick plate leisure batteries, 110ah. Once we found out that the charger should be left on we found that it would come on to equalise charging whenever lights or pump were being used, and only switch back to float charging once lights and pump were both off.

 

Then I got offered 2 brand new mercedes truck batteries for 100 quid, and they are maintenance free and only 100ah. They do not seem to have made any improvment and in fact are a little weaker.

 

So my questions are:

 

1. Is it normal that the numax is permanently on equalise charging (ie fan comes on) whenever any device powered by the batteries is on? And if so are there any alternatives that make less noise? Yes, once the demands on the system from lights etc, exceeds about an amp, the voltage will dip and the charger will switch to charging (bulk/absorption) mode rather than float. A phycially larger and more expensive charger is likely to make less noise for a given output, but it would be much cheaper just to locate the charger somewhere where the noise is not annoying!

2. What is the difference between equalise and float charging and should I expect float charging to stop after a prolonged period of no device being used? What you are describing as "equalise" is done at a higher voltage, probably around 14.4v, whereas once the charger switches to float the voltage will be reduced to prevent over-charging the batteries. It also seems to be current limited in Float to around 1A. The charger will and can safely remain in float mode indefinitely when you are not using any electrical devices on the boat.

3. I have an inkling that there may well have been nothing wrong with the old batteries and that this is why the new ones appear to be weaker, as they are an inferior spec, and if both new and old are in good order, new would therefore appear weaker. How is it best to test this? The only realistic way to test is to fully charge them, then measure how much charge can be taken out of them before they go flat

4. Does it even matter if the batteries are shot if we are permanently connected to shore? Will we be using more shore power with duff batteries or not? Probably not unless they are shot to the point that a cell is shorted. The batteries are just acting as a reservoir for possible moments when the demand you place on the electrical system exceeds the charger max output. If the bats get really bad a cell may short and pull down the system voltage so that the charger is always at high output and the power is going to "boiling" the water in the batteries into hydrogen and oxygen, which can be dangerous. I think you are a long way from that though.

 

Thanks a lot for looking

 

Dave on Newlyn

Edited May 28, 2013 by nicknorman

[Emonaboat]

Thanks a lot Nick, very helpful. I only described it as equalising charging as that is what it says on the LCD display on the Numax as soon as any 12v device is switched on. Is it just their term for it? Anyway, thanks its a lot clearer now.

[Stormbringer]

I have one of these Numax chargers on my other boat, and whilst it seems to work very well electrically

it's a noisy little bleeder!

It does exactly as you say, but being the 20A one, it only has coloured leds for stage identification.

 

I seem to remember a thread a while back where someone replaced the fan with a quieter one

In fact I think I might do this too...

 

Cheers

Andy

 

Edited to put interfering phone know it all correction in its place...grrrr.

Edited May 28, 2013 by Stormbringer

[smileypete]

If the halogen lights were replaced with LEDs then having the charger off during the day and on for some hours overnight or in the morning should keep the batts charged up if they're in reasonable nick.

 

If the previous owner used 100W of lights then only recharged every few days that would probably result in flat batteries and possibly early batt replacement.

 

cheers, Pete.

~smpt~

[Geoff Taylor]

Hi,I have the Numax 10 amp model looking after 4 leisure batteries very well and it too cuts the fan in when lights are on and goes back into silent mode approx 1 minute when all off, this I assume is because my batteries are in good condition (they are 3 yrs old) and go back into float mode very quickly. I test them from time to time with a Snap on tools digital tester and have never yet had to top up any to date. While cruising a 70amp alternator sorts them out and runs a 2KW inverter, 230v fridge,TV and lighting perfectly ok.

[Emonaboat]

Thanks for your input guys, lots to experiment with.