Battery charging

[Col_T]

Mornin' all,

 

Our boat lives in a marina with shoreline power supply left plugged-in, and live, whilst we are away. The boat has a Sterling Pro-Combi inverter / charger which acts as a battery charger when plugged into a live shoreline connection, so is constantly charging the bank of sealed lead acid batteries. We run tube heaters, controlled by electronic timers, to try and prevent the boat freezing up.

 

A couple of simple questions.

 

1:- is leaving the batteries on charge permanently doing them any harm?

2:- suppose I wanted to take a resting battery voltage reading on return to the boat - would the batteries be rested if they've been on a 'trickle charge' for a few hours, or do they need to be disconnected from all load / charge for a couple of hours before taking reading? Indeed, does each battery have to be completely isolated from everything before taking the reading?

 

Apologies for 'numpty' questions, but though I am trying to get some understanding of electrics I know I have a huge amount still to learn.

 

Thanks in advance,

 

 

Colin T.

[WotEver]

Hi Col,

 

1. No. You couldn't look after them any better.

 

2. There is little point in taking such a reading as (unless they're broken) they will all show a full charge. However, if you wish to do so then, with the charger disconnected, turn on the tunnel light for 10 minutes. That should hopefully remove the surface charge. If you want to also disconnect them and check them individually then yes you could, but again I doubt the need unless something suggests to you that one might be faulty.

 

Hope that helps

Tony

[nicknorman]

1: No, provided the charger is at an appropriate voltage, slightly dependant on the particular type of battery but typically 13.25v adjusted for temperature.

 

2: No the batteries have to be completely isolated from everything, and left for a period. In the case of batteries that have been on charge I'd say the "period" would be at least 24 hours, or alternatively take some charge out and then leave for an hour or so. This is because of the surface charge effect which will retain a higher voltage on the batteries for a long time, if the batteries are not being discharged.

 

But if your batteries have been connected to a charger, surely they will be fully charged and a measure of open circuit voltage is superfluous?

[Richard10002]

How old is your Pro Combi? I gave an older model where, if the shore power fails, the inverter kicks in, and flattens the batteries, so I can't leave it on charge unattended. I think later models have a charge only facility?

[Col_T]

Many thanks for the responses.

 

The Pro-Combi is set to charge sealed lead acids, via the dial selector on the front of the unit so, hopefully, they'll be getting the correct charging voltage.

 

The resting voltage check question was purely educational, so thanks for the comments and for explaining the logic behind those comments. I didn't think I needed to do one, but didn't know how to even if I did need to, though I had seen reference to this in other battery related threads.

 

I too have had the 'running the batteries flat' concern about the Pro Combi. I suspect that I'm being naive and/ or optimistic but I reckon there are two failure points - me running out of credit at the power distribution point on the pontoon, and the power supply to the pontoon going belly up. There are live aboards on either side of us so I'm hoping the marina would be fairly prompt in rectifying power failure to the pontoon, and should be able to fix any problem within a week. I go down to boat every 2 or 3 weeks at the moment, just to make sure it's still afloat as much as anything - it's our first boat and we only bought it last July so we're still at that worrying about it stage! I've done some fairly rudimentary calculations which make me think that the batteries should be able to cope with powering the tube heaters via the inverters for a couple of weeks, so I'm hoping that I'll get away with it. Still, nothing like tempting providence, is there?!

 

Once again, thanks for the replies.

 

 

Colin T.

[Richard10002]

My Pro Combi 2500W uses about 4A even when powering nothing, so 100Ah per day, 700Ah per week. How big is your battery bank, and how truly sure are you that your neighbours etc. will fix the power out, when there is one, (inevitable, over time??).

 

I dont have access to shore power, so use a generator, and am always nearby when the inverter charger is inverting, or charging.

 

I actually have a second 25A charger which came with the boat, and which I would use if I was leaving the boat attached to shore power. There is no way I would leave my inverter charger on shore power whilst away for a few days, never mind weeks.

 

I cant believe Sterling ever made such a poorly designed piece of kit, and am disappointed that they dont offer existing owners of the older model a cheap upgrade to the new - but that's how it is

[Loafer]

Many thanks for the responses.

 

The Pro-Combi is set to charge sealed lead acids, via the dial selector on the front of the unit so, hopefully, they'll be getting the correct charging voltage.

 

The resting voltage check question was purely educational, so thanks for the comments and for explaining the logic behind those comments. I didn't think I needed to do one, but didn't know how to even if I did need to, though I had seen reference to this in other battery related threads.

 

I too have had the 'running the batteries flat' concern about the Pro Combi. I suspect that I'm being naive and/ or optimistic but I reckon there are two failure points - me running out of credit at the power distribution point on the pontoon, and the power supply to the pontoon going belly up. There are live aboards on either side of us so I'm hoping the marina would be fairly prompt in rectifying power failure to the pontoon, and should be able to fix any problem within a week. I go down to boat every 2 or 3 weeks at the moment, just to make sure it's still afloat as much as anything - it's our first boat and we only bought it last July so we're still at that worrying about it stage! I've done some fairly rudimentary calculations which make me think that the batteries should be able to cope with powering the tube heaters via the inverters for a couple of weeks, so I'm hoping that I'll get away with it. Still, nothing like tempting providence, is there?!

 

Once again, thanks for the replies.

 

 

Colin T.

 

I have already apologised in other threads about my current disability (beer) but I'm thinking:

 

Does your combi have a pass-through facility, whereby it passes on the shore power mains when available, but doesn't replace that with the combi's own inverter, if and when the external mains fails?

[Richard10002]

 

I have already apologised in other threads about my current disability (beer) but I'm thinking:

 

Does your combi have a pass-through facility, whereby it passes on the shore power mains when available, but doesn't replace that with the combi's own inverter, if and when the external mains fails?

 

I asked that earlier.. if they have the older model like I have, it switches to inverter if shore power fails, (or if the genny stops in my case), and drains the bateries. The answers suggest they have the older model.

 

There is a newer model with the same name, but with a modification that allows you to set charger only - I think Victrons and Mastervolts have had this facility for much longer, if not forever.

[nicknorman]

I asked that earlier.. if they have the older model like I have, it switches to inverter if shore power fails, (or if the genny stops in my case), and drains the bateries. The answers suggest they have the older model.

 

There is a newer model with the same name, but with a modification that allows you to set charger only - I think Victrons and Mastervolts have had this facility for much longer, if not forever.

It would seem a pretty basic requirement for any Combi.

[Richard10002]

It would seem a pretty basic requirement for any Combi.

You would think so wouldn't you? I was very disappointed when Charles Sterling sent me an email telling me it would be a function of next year's model

[Col_T]

Cricket, you boys stay up late!!!

 

The Pro Combi is one of the older models e.g. automatically switches to inverter if the shoreline power fails.

 

Richard,

The 4A you mention, is this something you have measured or is it taken from the technical specs? Only asking as it would be interesting to know what my 1500W uses - I knew that the inverter would use some power but really hadn't imagined it would be that much, to be honest, and given that info your approach looks far more sensible.

 

Right, work calls, so I'd better drag myself away.

 

Thanks for the replies.

 

 

Colin T.

[WotEver]

Colin, if you have access to a decent marine electrician it wouldn't be a huge job for him to make a 'disconnect' box. It would simply comprise of a high current relay in the leads from the batteries to the combi, the coil fed by the incoming mains. A bypass switch (essentially a battery isolator switch) would bypass the relay when you are in attendance.

 

With the bypass switch turned off and incoming mains present the relay connects the combi as normal. If the mains disappears the relay disconnects the combi.

 

Tony

[Richard10002]

Cricket, you boys stay up late!!!

The Pro Combi is one of the older models e.g. automatically switches to inverter if the shoreline power fails.

Richard,

The 4A you mention, is this something you have measured or is it taken from the technical specs? Only asking as it would be interesting to know what my 1500W uses - I knew that the inverter would use some power but really hadn't imagined it would be that much, to be honest, and given that info your approach looks far more sensible.

 

The 4A is the reading on my NASA BM2 checked with a Uni-T clamp ammeter.

 

I think Sterling claim a low figure in their blurb, but don't actually quote a number. I haven't checked it in power saving mode, but power saving mode has never been able to start up the inverter when I connect most of the things I want to power... laptop charger, shaver charger, and other low power stuff. I think it needs to see more than a little power draw to wake it up.

[nicknorman]

4A is a lot. It's <1A for my mastervolt 2.5kw Combi and that is without any power saving modes selected.

[smileypete]

So is it fine to leave batts unattended on a high power charge source, with no way of monitoring if they are starting to go defective?

[nicknorman]

So is it fine to leave batts unattended on a high power charge source, with no way of monitoring if they are starting to go defective?

Following the scare stories, I always turn the max current on my 100A Combi down to 20A when leaving the boat unattended. However I think you could make a judgement call on the age and condition of the batteries and thus probability of a cell short.

[Richard10002]

4A is a lot. It's <1A for my mastervolt 2.5kw Combi and that is without any power saving modes selected.

Agreed, and I think I have seen posts where people have said the Sterling deny it is that high, but it is on mine. It's 1A in power saving mode but, as mentioned above, it will only wake up if asked to power something powerful

 

I think it's fair to say that it wasn't the best inverter charger. It's probably better now it can charge batteries with the inverter facility disabled, and one would hope the new model draws less in standby, but I'd bet it doesn't.

[Tony Brooks]

One other point about leaving batteries on charge for long periods unattended.

 

If a cell or cells start to short out internal, and that is the mots likely failure mode on a battery that has been kept very well charged over the years, the cell will start to gas more an eventually dry out. Not only will it produce a horrible smell but will also tarnish bright metal and may set off smoke/CO alarms. It is also possible that the battery will explode. When you are in attendance you will probably small the problem before much danger of explosion.

 

It is undeniably better to leave the batteries on charge from a SUITABLE multi-stage charge but if the ends of the battery are belling out, one or more cells demand more topping up than the rest, or one cell is getting hotter or bubbling more than the rest then please do not leave the batteries on charge unattended. Best buy new ones.

[Detling]

The wonders of solar. 300Watts of panel keep us independent in summer don't need to charge with fossil fuel, and in winter give a couple of amps for a few hours most days to keep the batteries topped up.

[Col_T]

Thanks for the replies, folks, and apologies for not responding to them earlier.

 

Something that wasn't clear in the OP is that the batteries being left on charge permanently is a happy by-product of leaving tube heaters on - we do winterize the boat e.g. draining water tanks and pipes, leaving taps open, etc. but the tube heaters are an attempt to prevent the boat freezing.

 

In summary, leaving the batteries on trickle / float charge is the best thing one can do for them until one, or more, on the bank start to fail at which point leaving them unattended is potentially the worst thing one can do for 'em. There are a couple of potential work-rounds, the first being the 'disconnect' box suggested by WotEver (post 12), the other being to install a 13 amp socket between the shore-line socket and the pro-combi (actually, between the galvanic isolator and the pro-combi) - something I've dreamed up, though this might not work of course as the thought is that the pro-combi would not be switched on. The first work-round has the advantage that the batteries can be left on charge, though that'll be an unattended charge which may be a disadvantage. The other work-round has the dis-advantage that the batteries are not being charged at all!

 

You folk have both increased my knowledge (much appreciated so many thanks) and given me something to think about (not quite so much appreciated but thanks none the less!).

 

That's about it for now.

 

Over and out,

 

 

Colin T.

[nb Innisfree]

Over a period of 3 years we used to fully charge our AGMs then leave them disconnected and off charge and leave the boat for a few months, longest period was 5 months and on return SoC was around 97-98%.