Battery charger low output

[Dazedkipper]

I have a Guest switch mode 5A dual output charger feeding the engine and domestic batteries automatically when on shore supply. Also I have a Driftgate alternator boost charge controller that is sensed on the domestic batteries. The problem I have is that on shore supply the domestic (and I assume also the engine) batteries are never fully charged because fter say departing a marina it can take up to 2-3 hours motoring for the alternator to bring the charge up.
So I gues I'm wondering if there may be something amiss, although all connections are bright and shiny, or is it possible to increase the charger float voltage?

 

[KenMcCulloch]

I'm not sure why starting the engine and motoring out of a harbour would discharge your domestic batteries? Perhaps I have misunderstood?

If your charger is doing what it's made for your batteries should be well charged every time you go out. Tell us more, number, size of batteries? Does the charger have a single or multiple outputs etc.

 

[Dave_Seager]

There are two factors to consider here. One is that the mains charger is set to charge to lower voltage that the engine starting system. The other is that you use up some of the stored charge to start the engine(s). The heaters and starter motors on a diesel engine each draw quite high currents. You can often observe this effect on cars where the alternator belt squeals when the engine is first started due to the extra load on the alternator to replace the lost charge.

 

[earlybird]

What is the output voltage of your shore charger? It should be at least around 13.8 volts on float, if significantly less then it's probably not working properly.
How are you assessing the state of charge of your batteries when you say that 2-3 hrs motoring is required to bring the charge up?
The Driftgate controller only cuts in to "boost" if the domestic bank is <12.6 volts, I think that's the spec. If it's going straight to boost, i.e. amber LED, on start-up, then it's another sign that your shore charger isn't working.
Once the controller does go into boost mode, it is programmed to cycle between boost/float several times over a period of 1-2 hours.

 

[pvb]

A 5A charger is quite small, and Guest probably suggest a maximum battery size of around 100Ah. If you have a larger domestic battery bank, the charger may not charge it adequately. It's likely that it charges at about 14.5v max, and your alternator output could well be higher than that, so you will see some charge when the engine's running.

Do you know the model number of the Guest charger?

 

[Barry Jones]

A couple of questions.

How old are your batteries (both starter and domestic) ??

Are you sure the Driftgate is set up for the correct battery type ??

Are you assuming that the batteries should be fully charged because they have been on charge for so long ??

I have a Guest switch mode 5A dual output charger feeding the engine and domestic batteries automatically when on shore supply. Also I have a Driftgate alternator boost charge controller that is sensed on the domestic batteries. The problem I have is that on shore supply the domestic (and I assume also the engine) batteries are never fully charged because fter say departing a marina it can take up to 2-3 hours motoring for the alternator to bring the charge up.
So I gues I'm wondering if there may be something amiss, although all connections are bright and shiny, or is it possible to increase the charger float voltage?

 

[pappaecho]

I had a similar problem earlier this year with my new old boat, with two battery banks of unknown vintage.

I suspect you have a duff battery, which is carrying down the others. A battery bank on mains power should be fully charged after a couple of days, and thereafter only needs to provide enough charge to make up for the self discharge,

I suggest that you undergo a test to isolate the rogue. Charge the batteries to at least 12.8 volts. Disconnect the batteries completely from the loom and each other. Monitor the voltage over 24 hours and thereafter daily. In my case the rogue battery was obvious after a few hours, and was at 10.5 volts after 36 hours, whilst the others were all at about 12.6 volts - roughly fully charged.

 

[Dazedkipper]

Firstly an apology, the charger is 15A.

The measured float voltage on the domestic batteries is 13.8V.

The driftgate senses to the domestic batteries (2x85Ah) and boost charges at 14.5v.

I can't remember if the driftgate is programmed to always run at boost on start-up or only if the battery voltage is low, if it is then I would expect if the batteries were fully charged by the shore supply to only run for one cycle then to fall back to the alternator regulator. If it isn't then I'd expect it to not go to boost at all if again the batteries were fully charged.

My feeling is that the Guest isn't charging fully before going to float but the float voltage is correct. I note that the new Guest chargers have a high and low output and am wondering if mine is the same although is is a few years old.

 

[William_H]

Charging

If a battery has 13.8 volts measured at the terminals then it must be either charged or taking charge and will eventually be charged. So the charger must be fine. However there seems to be a move toward higher charging voltages which will charge faster and possibly more completely.
I would suggest that if your alternator controller when it gets a go reckons the batteries are not charged then it may be set too high. ie to expect too much voltage. Obviously if the alt controller puts 14.8 volts on the batteries more is going to go in whether it needs it or not. it may result in over charge.

re PVB comment about 5 amp charger being too small. (I realise yours is actually a15A) Well in practical terms that may be so however there is no reason why a 5amp charger will not charge the biggest of batteries. It will take longer for a very depleted battery and the charger will be putting out 5amps for a long time but provided the charger exceeds the natural discharge rate of the batteries then it will charge them.

good luck olewill

 

[PeterGibbs]

I have a Guest switch mode 5A dual output charger feeding the engine and domestic batteries automatically when on shore supply. Also I have a Driftgate alternator boost charge controller that is sensed on the domestic batteries. The problem I have is that on shore supply the domestic (and I assume also the engine) batteries are never fully charged because fter say departing a marina it can take up to 2-3 hours motoring for the alternator to bring the charge up.
So I gues I'm wondering if there may be something amiss, although all connections are bright and shiny, or is it possible to increase the charger float voltage?

Not enough amperage for this battery load. Need 20 amp capacity for shore based charging; the engine alternator delivers 40-50 mps but usually without phased output.
Not very satisfactory - especially if the battery types are mixed.

Not fully charging is also a sign the batteries (or one cell in one of them) are duff or dying.
Typically you charge the battery, it immediatley reads 13V - wonderful. 10 mins later it's fallen off to less than 12V - failure to hold the charge! Goodbye old battery, hello new one.

PWG