Battery Charger Question

[abraxus]

Hi

Not being a battery charging expert I wonder if anyone can help me with an answer to my question.

I'm about to fit a Sterling Pro Charge charger into my boat. I have two banks of batteries and the charger has three outputs.

I also understand that the charger is a power pack, and so it will directly power the 12v circuit on board, whether there are batteries in place or not.

If I wire the charger to each bank, then it will charge my batteries and power my 12v stuff. However if I switch off the batteries at the switch, to prevent them being inadvertantly drained by a power outage to the charger, then I also disconnect the charger from the 12v circuit.

What I'd like to do is have the charger connected to the 12v circuit, connected to the batteries to charge them, but also be able to disconnect the batteries from the 12v house circuit.

Is there a way to wire the charger so that it can charge the batteries, power the 12v onboard circuit, but be able to isolate the batteries from the house circuit by turning off the switch?

On paper it would seem that this could be achieved by wiring the third (spare) output from the charger to the "common" post on the 1,2,off switch, which would directly connect the charger to the onboard circuit and allow me to disconnect the batteries. However, I'm not sure how these "smart" chargers work, and whether having the third output connected directly woud affect the chargers sensing capabilities.

Can anyone advise?

Thanks.

 

[westernman]

Are you sure it is a 1,2,3, off switch??

I have only seen 1,2, both, off switches.

My battery charger is connected directly to the batteries. I.e. charges the batteries even with the 1,2,both,off switch off. If I wish to power on board stuff, then I have to switch to 1,2, or both.

I think this arrangement is the usual one.

 

[Deleted member 36384]

I have installed this charger and I am sure that it does not act as a "power pack" i.e. it feeds in 12 V to a yachts wiring just by itself. The instructions clearly state that if two of the outputs are being used, the 3rd should be hard wired to one of the other outputs.

I am now out with my depth big time, however, I imagine the control logic within the charger would sense incorrectly if the 3rd output was wired directly into the yachts wiring. It is not clear to me that the charger actually charges all three banks independently at the appropriate stage in the charging profile. It may just detect the one that needs charging the most, charge that up, then switch to the next bank and charge that up, then do what ever it does to maintain the charge. I do not know though, its not clear from the instructions that came with mine.

 

[Deleted member 36384]

http://www.ybw.com/forums/showthread.php?304411-Ctek-or-Sterling

Check out Post No 5 by "conctentrik" who has talked to Sterling about this very function - it doesn't work as a power pack wired directly to the yachts wiring. The power pack function means that when the batteries are topped up, it will keep up with demand from the yacht up to a point, thus not draining the batteries.

Its worth reading the whole thread noted above. A poster states that with all batteries disconnected from the charger the Sterling will act as a power pack. It also looks like it cant act as a power pack and charger if the batteries are connected and being sensed by the charger.

 

[abraxus]

Are you sure it is a 1,2,3, off switch??

You're right, it's a 1,2,off switch. Typo on my part, will edit.

My battery charger is connected directly to the batteries. I.e. charges the batteries even with the 1,2,both,off switch off. If I wish to power on board stuff, then I have to switch to 1,2, or both.

I think this arrangement is the usual one.

Yep that's the usual way, and the way mine is wired, but I guess I'm looking for the unusual in that I want power on board without the batteries.

 

[abraxus]

Thanks BlowingOldBoots

I've just read that thread and, coupled with my other reading, here's what I've concluded:

The charger can act as a power pack, in that if the batteries were removed and the charger remained connected then it would still power the 12v onboard load.

However it appears that my suspicion was right, in that leaving it connected to the batteries as well as directly to the house load then it interferes with the sensing function and it becomes a "dumb" charger rather than a smart one.

In any event I've dropped a line to Sterling to see what they say and will await their repsonse.

 

[JimC]

Yep that's the usual way, and the way mine is wired, but I guess I'm looking for the unusual in that I want power on board without the batteries.

Do Sterling actually say that the charger can be used in this way? If not I would be wary of your proposed use because the raw output from the charger, with no battery to smooth it, could be dangerously rough for the electrical equipment you plan to run. Some chargers have high voltage pulses in their output which are intended to de-sulphate the batteries. These wouldn't do your instruments any good.

 

[ianj99]

I'm fairly sure it cannot act as a power pack without having at least one battery connected.

The 3 outputs are just paralled (in effect but via mosfets to isolate them from each other) - ie each output is not sensed & controlled separately so the charger will always sense and react to the flattest battery.

With no batteries connected, it has nothing to sense so may assume the non existent battery is flat and therefore not operate in power pack mode.

The correct way to wire the charger is to connect it directly to the batteries and NOT via the isolator so the problem you fear can't occur and you don't need to concern yourself with power pack modes etc.
Ian

 

[abraxus]

I'm fairly sure it cannot act as a power pack without having at least one battery connected.

According to Sterling it is also a power pack and according to this link it can supply power with no batteries connected Ian (see bottom of page):

http://www.pbase.com/mainecruising/installing_a_marine_battery_charger

The correct way to wire the charger is to connect it directly to the batteries and NOT via the isolator so the problem you fear can't occur and you don't need to concern yourself with power pack modes etc.
Ian

I appreciate that's the correct way, and do want the charger to be connected directly to the battery, but also to the house load.

The problem I fear is a power surge at the marina that trips my ac breaker. If that happens then my fridge will drain my batteries, as the tripped breaker wont allow the charger to come back on when the marina power is restored.

If I have a power pack powering my fridge then I can switch off the batteries and still have the fridge running. If the ac breaker trips I just lose power to the charger and power pack and so end up with a warm fridge at worst, but at least my batteries don't get drained.

Does that make sense?

 

[ianj99]

According to Sterling it is also a power pack and according to this link it can supply power with no batteries connected Ian (see bottom of page):

http://www.pbase.com/mainecruising/installing_a_marine_battery_charger




I appreciate that's the correct way, and do want the charger to be connected directly to the battery, but also to the house load.

The problem I fear is a power surge at the marina that trips my ac breaker. If that happens then my fridge will drain my batteries, as the tripped breaker wont allow the charger to come back on when the marina power is restored.

If I have a power pack powering my fridge then I can switch off the batteries and still have the fridge running. If the ac breaker trips I just lose power to the charger and power pack and so end up with a warm fridge at worst, but at least my batteries don't get drained.

Does that make sense?

I can see your point, but there is a simple solution:-
I'd simply fit a relay to one of the charger outputs, with the fridge supplied via the normally open contacts from the house battery. Then if the charger goes off or fails (my Procharge D did but lets not go there!) the fridge will be disconnected from the battery.

Ian

 

[DaveS]

According to Sterling it is also a power pack and according to this link it can supply power with no batteries connected Ian (see bottom of page):

http://www.pbase.com/mainecruising/installing_a_marine_battery_charger




I appreciate that's the correct way, and do want the charger to be connected directly to the battery, but also to the house load.

The problem I fear is a power surge at the marina that trips my ac breaker. If that happens then my fridge will drain my batteries, as the tripped breaker wont allow the charger to come back on when the marina power is restored.

If I have a power pack powering my fridge then I can switch off the batteries and still have the fridge running. If the ac breaker trips I just lose power to the charger and power pack and so end up with a warm fridge at worst, but at least my batteries don't get drained.

Does that make sense?

I was faced with the same issue, but adopted a different solution. I wired the charger to both battery banks in recommended fashion. I then fitted a VSR to the fridge circuit, so that the fridge would only operate when the batteries were on charge either from the shore power charger or the alternator. This worked reasonably well, but with the batteries fully charged and the charger at float voltage the VSR would occasionally drop out and not come back on.

To overcome this I fitted a relay in parallel with it which would close whenever the charger was on, regardless of its output voltage. I tried to power this relay from the third output wire of the Sterling charge controller, but much to my surprise this didn't work: the relay stayed on when the charger was switched off. I discovered that with the charger off battery voltage appeared on this third charging wire if either of the others was connected to a battery, which does rather call into question just how much isolation actually exists between the outputs. I don't know whether this is a fault with my charger or a more general "feature". I resorted to taking a feed via a 240V relay with its coil in parallel with the charger: this works and stops the fridge on loss of shore power, but isn't ideal: it would be fooled if the charger failed and didn't trip its supplying MCB.

 

[ianj99]

Maybe the third output didn't switch on due to the relay being an inadequate load, so try a 12v 10watt bulb in parallel with the relay. I'm sure the outputs will be isolated otherwise you may as well parallel all the batteries and just have one output!

Your mains relay method would be the other way to do it and I use this method to switch on my mains inverter.
Ian

 

[abraxus]

Ian/Dave

Thanks, it seems that a relay would be the way to go.

I guess the only other alternative is to switch to the starter battery whenever I leave the boat. That way if the worst happens then I'm only discharging one cheapish battery as opposed to a house bank of three.

 

[DaveS]

Maybe the third output didn't switch on due to the relay being an inadequate load, so try a 12v 10watt bulb in parallel with the relay. I'm sure the outputs will be isolated otherwise you may as well parallel all the batteries and just have one output!

No, the problem was that the relay wouldn't switch off - unless both other charging wires were disconnected from the batteries. As you say, looking very much as if the three outputs were simply connected in parallel. An earlier post stated that are isolated using FETs but if this is so then, at least for my charger, they have either failed short circuit or are somehow being held on, presumably using battery power.

 

[ianj99]

No, the problem was that the relay wouldn't switch off - unless both other charging wires were disconnected from the batteries. As you say, looking very much as if the three outputs were simply connected in parallel.

This may simply due to a few ma of leakage between the outputs. Something that took a bit more current in parallel with the relay may have solved this.
Ian

 

[DaveS]

This may simply due to a few ma of leakage between the outputs. Something that took a bit more current in parallel with the relay may have solved this.
Ian

I'm not convinced. I would expect leakage through a FET to be in µA if measurable at all, and the relay is an automotive type with a 100Ω coil so its taking around 120mA.

 

[nigelmercier]

According to Sterling...

According to Sterling it probably does a lot of things. Doesn't mean that it does.

If you haven't bought it, consider a CTEK.

 

[pvb]

The problem I fear is a power surge at the marina that trips my ac breaker. If that happens then my fridge will drain my batteries, as the tripped breaker wont allow the charger to come back on when the marina power is restored.

A possible solution would be to run the fridge via a Sterling ProLatch R - this has a "battery protection" setting which will disconnect the fridge if the voltage drops below 12.4v (adjustable). The advantage of this is that you'd still be able to run the fridge without shorepower or engine running as long as the batteries are fairly well charged, but you wouldn't have any risk of the fridge flattening the batteries.

 

[ianj99]

I'm not convinced. I would expect leakage through a FET to be in µA if measurable at all, and the relay is an automotive type with a 100Ω coil so its taking around 120mA.

I agree, but I was trying to explain why the relay stayed closed. Clearly the outputs are not directly connected to each other, so what other explanation is there?

Alternatively, each output could have a 100R (or so) to the voltage sensing input on the microcontroller which means there is a few ma flowing between the outputs (those that are connected to a battery or load).

Putting a 10watt bulb across the relay would prove this.

 

[abraxus]

According to Sterling it probably does a lot of things. Doesn't mean that it does.

Possibly so, as I asked Sterling and they've now replied saying to use the third output on the charger to bypa,ss the batteries and wire direct to the house load. I know that that this will work in terms of powering my 12v circuit without the batteries but am not convinced it wont bugger up the sensing capabilities of the charger.

If you haven't bought it, consider a CTEK.

Actually I looked at the CTEK but they only go up to 25amps and with 625ah of batteries I wanted something larger. Also the CTEK is 240v only and my existing charger is 110v via a transformer and so the wiring of the Sterling woud be simpler.