Battery charger as power supply?

[davidpbo]

Currently sitting in Marina with access to mains power which is unusual for us.

What is the downside of using a Halfords constant current battery charger which switches to maintenance mode when charge completed as charger whilst running one or two 20w bulbs? The battery sits under companionway stairs.

Cabin door has a vent in it. Considering leaving it on tonight as battery down. I appreciate charging will take longer but what is the risk of hydrogen build up? We don't have gas alarms.

 

[VicMallows]

Why are you concerned? ... sounds completely normal to me. (Unless this is some absolutely huge ancient garage type boost charger with no voltage regulation whatsoever )

 

[TopDonkey]

There is no risk at all, when i first bought my boat and was working on it, i used a halfords charger for 6 months constantly connected and used the power it provided for all the onboard systems without issue

 

[Burnham Bob]

I was always under the impression that the battery charger output - in terms of amps - drops as the battery charges up. Hence the drop shown on the ammeter on some units. So the system is self limiting.

In my caravan, the charger is on all the time (albeit I think it's a dedicated special unit) but the 12 volt battery is always in line with the charger topping it up as the 12 volt loads drain the battery.

 

[halcyon]

I was always under the impression that the battery charger output - in terms of amps - drops as the battery charges up. Hence the drop shown on the ammeter on some units. So the system is self limiting.
.

It's a yes and no.

Cheap basic charger rate the output at 12 volt, you can never get 12 volt with a battery on charge. So charge is never what they claim, and it falls as battery is charged due to lack of power.

When I built chargers I rated them at 14.2 volt, so you had constant rated current to that point. Once you reached 14.2 volt amperage will fall due to battery chemistry.

We always based the system on running 24 hours when owner was on board. the theory was that when you switched on, it provided a power supply to cover domestic loads. Then when you went to bed, it would charge up domestic battery bank, then engine batteries, then drop to float charge or later a maintenance phase.

So yes charging over night is okay, but depending on charger spec.

Brian

 

[Plevier]

When I built chargers I rated them at 14.2 volt, so you had constant rated current to that point. Once you reached 14.2 volt amperage will fall due to battery chemistry.

We always based the system on running 24 hours when owner was on board. the theory was that when you switched on, it provided a power supply to cover domestic loads. Then when you went to bed, it would charge up domestic battery bank, then engine batteries, then drop to float charge or later a maintenance phase.

Brian

I know this isn't a new question but I have yet to hear a satisfactory answer.

Been on for a while, battery fully charged, charger has dropped to float voltage.
Owner comes on and turns on all the lights, or the fridge comes on or something.
Can you avoid the charger switching to 14.2V which is undesirable for the battery?

 

[halcyon]

I know this isn't a new question but I have yet to hear a satisfactory answer.

Been on for a while, battery fully charged, charger has dropped to float voltage.
Owner comes on and turns on all the lights, or the fridge comes on or something.
Can you avoid the charger switching to 14.2V which is undesirable for the battery?

It's purely a battery charger design issue, if the charger is designed to supply full output at float voltage, then unless a very high load, it should maintain float voltage. but some chargers cut in so they can claim another charge phase in the marketing, or it could be limited float output current.

Only way to avoid it is to check charger spec when you buy it I'm afraid.

Brian

 

[VicS]

It's purely a battery charger design issue, if the charger is designed to supply full output at float voltage, then unless a very high load, it should maintain float voltage

This is how those chargers that are sold specifically as charger and power supply unit will work ??

 

[halcyon]

This is how those chargers that are sold specifically as charger and power supply unit will work ??

What's the point of selling a charger for a boat that does not ?

After all the circuit you use to regulate 14.2/14.4 or what ever, is the same circuit for float charge, thus the same rating.

Brian

 

[William_H]

Hydrogen build up

Back to the OP question on hydrogen build up. Batteries should always be ventilated especially when on charge. Of course the production of hydrogen depends on the charge current and level of charge. But I think OP is right to have concerns. The hydrogen can be ignited if allowed to build up. I can't really suggest a practical ventilation system for a boat.
Small aircraft have their battery in a sealed box. 2 tubes lead to outside air extending out through the skin. The tubes have an angled end so inlet facing open forward and outlet facing aft to provide air movement.
I think for safety I would stick with a low current charger and perhaps ensure that there is some ventilation in battery area to outside. But then it is perhaps not such a big concern....you decide. If you observe battery bubbling then more concern.... good luck olewill

 

[savageseadog]

It's a yes and no.

Cheap basic charger rate the output at 12 volt, you can never get 12 volt with a battery on charge. So charge is never what they claim, and it falls as battery is charged due to lack of power.

When I built chargers I rated them at 14.2 volt, so you had constant rated current to that point. Once you reached 14.2 volt amperage will fall due to battery chemistry.

And battery condition, a knackered battery will gas rather than charge.

 

[Plevier]

It's purely a battery charger design issue, if the charger is designed to supply full output at float voltage, then unless a very high load, it should maintain float voltage. but some chargers cut in so they can claim another charge phase in the marketing, or it could be limited float output current.

Only way to avoid it is to check charger spec when you buy it I'm afraid.

Brian

But if the current exceeds a threshold won't the charger think "Aha! Low battery! More vigorous charging needed." and switch to its higher output mode? As this is normally (AFAIK) voltage limited constant current, if the total load is within the charger's rating you're then giving the battery an undesired boost charge.
AFAICS that's what my Cristec one does - if the current goes up to more than a certain %age of its rating, it switches onto its timed 5 hour boost. The manual is not too clear. I think the figure is 20%, so with a 25A charger this raises the possibility of the fridge's activating it every time it cycles and you end up in boost mode permanently. (I don't think it's a very good unit, be as rude as you like! It's OEM on a Jeanneau. The Quick that Bav's use strike me as rather better.)
Is there a way round this? (I mean in designing a unit, not with regard to the Cristec.)
If you trap it so it needs a mains disconnect before it will go into high output mode again, you run the risk of not compensating for a genuine low battery situation.
Can you give an example of a commercially available charger that you think does deal with this properly? I'd like to look at all the info on it.

 

[halcyon]

And battery condition, a knackered battery will gas rather than charge.

Which is why I set 14.2 volt, a normal knackered battery will reach that voltage, and I fitted a fan control that would drive a blower fan to allow battery ventilation until charge dropped to float.

Brian

 

[halcyon]

Is there a way round this? (I mean in designing a unit, not with regard to the Cristec.)
If you trap it so it needs a mains disconnect before it will go into high output mode again, you run the risk of not compensating for a genuine low battery situation.

All I did was once in float mode, it stayed in float mode until the voltage fell below 12.9 volt. This indicated there had been demand higher than the charger could cope with, and there had been a drain on the battery capacity. It then did a charge cycle back to 14.2 volt to top up battery, no timed period, and then went back to float.

To-day either I'm getting very old, or there is a lot of odd design theories about.

Brian

 

[Plevier]

All I did was once in float mode, it stayed in float mode until the voltage fell below 12.9 volt. This indicated there had been demand higher than the charger could cope with, and there had been a drain on the battery capacity. It then did a charge cycle back to 14.2 volt to top up battery, no timed period, and then went back to float.

Sounds reasonable! Would need good regulation but that should not be a problem with SMPS should it? I'm not aware of any that operate like that though - will have to have another look.
Thanks.

 

[John H]

Sounds reasonable! Would need good regulation but that should not be a problem with SMPS should it? I'm not aware of any that operate like that though - will have to have another look.
Thanks.

The Victron BluePower charger that I have seems to base its idea of battery charging requirements on the time taken initially when in bulk mode to reach some threshold voltage. This seems to determine the time it subsequently spends in absorption mode, float etc so it is relatively unaffected by additional current demands. I've seen the 25A charger stay in float mode or maintenance mode while still meeting demands for an additional 6A or so (fridge comes on, faulty battery put in parallel for a charge!)

So I guess it depends upon the algorithm implemented by the charger - this Victron one seems good to me.