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StillCruising

Battery Monitoring

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Hi you knowledgeable folks I would value your thoughts on a little upgrade that I am considering. We have three batteries, two for the domestic supply and one for the starter. In simple terms all the negatives are joined together and a wire goes to the isolator switch the other side of this goes to the engine block and negative bus-bar. The starter positive goes straight to the starter motor, the two domestic positives are joined together and then go to a bus-bar and fuses. The alternator is a normal   Lucas type and has an old (probably original) ammeter in the line which when the engine is running shows the total charge to all the batteries.

The downside to the above set up is that you cannot measure the discharge from the domestic batteries and this was highlighted recently when a fault developed in the Ebber heater switch causing a large current drain. This has prompted me to think about fitting a NASA BM2 however the shunt goes in the negative line and if I did that it would measure the starter discharge and that is beyond its design parameters. To overcome this I am proposing split the link between the two domestic batteries and the starter battery and insert the shunt. The only disadvantage that I can see is that it will not measure the charge to the starter battery but then I’m not sure that it is necessary a big problem.

NB. For the sake of simplicity I have left the direct (but fused) feeds to the solar panel, bilge pump etc.

Does anybody see any issues with what I have outlined above of have any other suggestions?

Bob

Basic Battery Connections.doc

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Nowadays an ammeter is not necessary, and is a bit of a nuisance as all the charge from the alternator has to got through it before it goes anywhere else. This means very heavy wiring up to the dashboard and down again.

Why not replace the ammeter with a volt meter, wired positive to the start key "on" position and negative to anywhere on the common earth return? You could also fit one for the domestics, depending on what sort of charge splitting system you have. A good spot would be on the same line as the cigar lighter socket, that you use as a battery charging point for telephones, etc. (provided that socket is fed by the domestic batteries). As you wouldn't want one that is switched on all the time, maybe choose a type which has a row of LEDs that light up to show the charge when you press a button?

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Hi Bob Having the batt switch in the neg earth is not the best way but!! yes you can do this but knowing the charge rate of the alternator is not a lot of use it would be better and cheaper and easier to get two volt meters one for each batt bank these will tell you how much is in the batterys and how much charge each is taking. i would surjest a inteligant altenator regulator to maximise the potentail of its capisity along with quicker charging along with a split charge diode to isolate the two banks so you dont flatten the starter batt, and chage the batt leads so that the pos goes to one batt and neg attaced to other batt this will work both batts rather then the first one with the other one trailing still keep the pos  and neg connected ie parrail you most likly will only need to mov the neg or pos to the other battery. Johnimg004.thumb.jpg.8161b88f3190acadef135fe838ad3618.jpg

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How about one volt meter and a switch to access both banks. 

We have one voltmeter and three sets of batteries. One domestic  320ah, one for the inverter 320ah and one for the engine 160ah. The domestic and inverter banks go through an isolation switch which allows them to become one bank at the click of a switch. We have a selectable display ( analogue no digital stuff). We did all this to support original 1950s electrics and lamps, before we installed LED lighting.

With LED we have zero issues with battery power. 

How you set this up I am in the dark you lost me at I have as well.

 

M

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With a modern ARGOFET split charger you only need a small link cable to the battery monitor and given the greater efficiency etc that might be worth looking into.

They aren't the cheapest of things once you've bought all the bits, but it saves running enormo-cable to the dash.

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Hi Again.

Thanks for the replies. The boat was originally built (1980) with the isolator in the negative line, this is not the first boat that I have come across in this configuration so whilst maybe unusual is not unique. Provided the batteries can be isolated from the boat circuits it probably doesn’t matter which line the isolator is in, and I have no plans to change it. We have owned the boat for ten years and after the first few months with consistently undercharged batteries checked by their specific gravity I fitted a Sterling Pro Reg B and increased the thickness of the wiring both to carry the extra amperage available and reduce the line resistance caused by the long run to the ammeter and back. To maintain the batteries when the boat is moored up or not in use I have a 100watt solar panel with a Photonic Universe MPPT controller and the remote monitor which Is connected to the domestic batteries only, I can also link it to the starter battery if required e.g. over the winter months. The controller shows the voltage generated from the solar panel, the charge going to the batteries from it and the battery terminal voltage. I therefore know what the current that alternator is pushing out via the existing ammeter and the battery voltage via the Photonic remote.

This set up has served us well with no issues for many years but one day last autumn we found that the domestic battery (2x110ah) voltage was dropping very fast with just a few 10w 2D lights on which had never happened before. At first I suspected the alternator diodes as I have seen this before but by a process of elimination I found that although visually switched off on the rotary switch the Ebber was in fact drawing a pulsing 7 amps although there was no sign of it starting up. It turned out that the rotary switch whilst appearing to be in the OFF position was in fact still connecting to the heater on what should be its lowest heat setting. There is a detent in the switch that is supposed to hold it firmly in the OFF position but over the years this has become weak and can easily be moved just by dusting off the dash board. Personally I have never liked the rotary switch set up and we always run it flat out to avoid the clogging up that occurred to a friend’s system, so having taken the fuse out for now I will look to something a bit more foolproof in future.

The quickly flattening battery scenario above is what made me think about the possibility of measuring the actual current drain as we would have seen the pulsing but on thinking about it again and taking on board the comments and advice in the various responses to my original post I am not going to bother with the BM2 idea.

Finally I apologise if this post has got a bit wordy but I have tried to cover all the details and issues in one go hopefully without being two ‘techy’

Regards

Bob.

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I can't edit my previous post but the 2D lights are 15 watt not 10watt as stated.

Bob

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On the eberspacher their should be a yellow wire between the control and main unit, put a switch on it and leave the rotary dial full up and it should stay off unless the switch is activated, on the older control their was a separate switch for on/off and a dial for temp.

It is the yellow wire I power up for remote phone control so I can phone the heating when I get the last beer and get back to a toasty boat.

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Wow cheers Smoggy a separate switch  is exactly what I had in mind. I have PDF copy of the Ebber instructions on the PC but it looks like a copy of a copy and the wire colour code is virtually unreadable so I was struggling  to determine what colour the control wire is.

Thanks again

Bob 

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Hi Bob Sterling do positive shunts if you want currant flow. John

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Hi All.

Just a quick update.

Whist aboard last week I rechecked all the electrics. The engine charging and solar panel charging were working OK, instead of calculating I measured the current draw from each  light fitting (2D) and they were all around 1amp each (different wattage tubes in some of them). With everything switched off there was a very few milliamps draw probably from the USB adaptors.

With nothing sinister found on the current draw front I disconnected the batteries and checked them with a load tester. The 12year old starting battery was perfect however both the leisure batteries showed a significant drop in ‘on load’ voltage. So two new batteries were obtained and fitted and now everything is back to normal.

Although the leisure batteries were only two years old I know that whilst in a boatyard last year they had been left for a long time (three weeks)  with the ignition on and the Ebber pulsing (as described in my previous posts) so I’m assuming that they became sulphated and therefore whilst appearing to charge up OK they had very little capacity.

As mentioned by Smoggy I found the yellow feed wire on the Ebber but since I left the switch at home (doh) that mod will be for the next visit, in the meantime the fuse remains out.

Regards

Bob

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Hi Bob Yes that's the way to  destroy a battery,   it's not good practice to test a leisure batteries with a battery discharge tester as they have thin plats and they are not designed to give a large currant unlike starter batteries which have thicker plates and designed to give a large currant for a short time using a hydrometer gives best results as each cell can be different. John

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Hi John (annv).

I agree with your comment about it not being a good idea to use discharge testers on leisure batteries but it really was the last result to confirm a theory.

All the indications from the charging system pointed to the batteries being fully charged. when I checked the SG of all the cells they were all showing virtually the same same but not full charge (and no 'brown soup' to denote plate breakup). The other thing was that I could hear them gassing fairly vigorously with the solar panel only showing a couple of amps going in. I have seen this sort of thing before when I ran a garage  battery charging shop while working for London Transport many years ago where it was usually due to internal cell shorts or sulphaton. With that in mind I figured I hadn't got much to loose with a drop test which in this case proved the lack of capacity. I

Regards

Bob

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I have fitted two separate digital voltmeters and ammeters for the starter battery and domestic banks. Not a difficult job, and you can easily see exactly what's happening. Not the discharge current for the starter battery, of course! Battery voltage is expected to drop a few points while drawing large currents, but if it doesn't return to normal at rest then it's safe to assume there's a problem with capacity. Trouble with sealed batteries is, there's no way to check each cell with a hygrometer. My starter battery died, with one cell showing dead on the hygro, but was being charged to the correct voltage, and retaining that voltage at rest. Meaning the remaining cells were being overcharged. If it had been a sealed battery, I wouldn't have known, and might have assumed there was some high resistance problem in my wiring. Simple is best.

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The main reason if you have a dud battery for not drop testing is that the gas can explore, I had one in a van do just that, took it off charge, went to start and boom, battery and acid everywhere, lucky it was in the engine bay not under my seat.

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3 hours ago, grendel said:

gas can explore

There are few things in life that one needs to worry about, but gas going off exploring is certainly one of them. :-)

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Explode bleeping AutoCorrect

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I had to replace my old D2 heater controller on Trixie, not sure if it is the same as yours - switch on/off and the dial used to adjust heater output.  These are online for around £60.00

s-l640.jpg

I then have a NASA BM1 to keep an eye on the batteries, which tells me their voltage and amps - either charging or discharging. It is remarkably accurate when compared to a voltmeter but does need to be wired correctly and set up right. Two boatyards both had a go at this and got it wrong, in the end a Marine Electrician got it right and it has performed perfectly since.  I so however suspect my re-built Alternator is still unhappy but that is another story.

 

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