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Multimeter reading of 17v


hackenbush

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My comments really related to the typical type of wet battery that the OP is likely to be able to afford if he gets into replacements or additions. It isn't too helpful to him to know what the issues may be for something far more expensive, because he has made it clear that finances are tight.

 

I would still argue that for all practical purposes, just looking at the kind of wet cells likely to be bought, it will not matter if the name on them is different, or the stated capacity is.

 

Here's a thought I tried to raise already.....

Many of us have an arrangement with only one alternator, and some kind of split charging arrangement. Every time I start my engine, and connect the starter battery to the domestic bank, I am mixing batteries that have a different name on, are of different ages, and have different capacities. Not only that, it will normally be the case starter battery is already at 100% charge, or as near as damn it, whereas the domestics may be at (say) 60% or 70%. I can't say I have ever suffered unduly short life on a domestic bank, and certainly not on the starter battery by such treatment, and I certainly wouldn't dream of automatically replacing 5 domestic batteries just because I'm fitting a new starter battery. Well in fact I'm about to do just that, so I'll let you know if anything fails quickly as a result.

Edited by alan_fincher
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When we bought our boat it had four batteries of three different types. Two open cell, two sealed but different from each other. I thought "They will have to come out soon" and lowered my offer to allow for a new set of batteries. That mismatched set lasted a further 3 years before I retired them. Nothing bad happened they just got tired. Once I had them out I measured the resting voltage separately and 3 of them were OK but the 4th was way down like 10V

I replaced them with a matched set.

What I take from this is while keeping batteries in matched sets is good practice, mixing types and old and new isn't necessarily a disaster. So while I wouldn't recommend putting new batteries with old without seeing the situation, it can be done. Would the heathier 3 have lasted longer without the dud, I don't know

 

Top Cat

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My comments really related to the typical type of wet battery that the OP is likely to be able to afford if he gets into replacements or additions. It isn't too helpful to him to know what the issues may be for something far more expensive, because he has made it clear that finances are tight.

 

I would still argue that for all practical purposes, just looking at the kind of wet cells likely to be bought, it will not matter if the name on them is different, or the stated capacity is.

 

Here's a thought I tried to raise already.....

 

Many of us have an arrangement with only one alternator, and some kind of split charging arrangement. Every time I start my engine, and connect the starter battery to the domestic bank, I am mixing batteries that have a different name on, are of different ages, and have different capacities. Not only that, it will normally be the case starter battery is already at 100% charge, or as near as damn it, whereas the domestics may be at (say) 60% or 70%. I can't say I have ever suffered unduly short life on a domestic bank, and certainly not on the starter battery by such treatment, and I certainly wouldn't dream of automatically replacing 5 domestic batteries just because I'm fitting a new starter battery. Well in fact I'm about to do just that, so I'll let you know if anything fails quickly as a result.

 

The trouble us with making all encompassing statement like the one in your 2nd paragraph is that if something goes wrong who is responsible. Now that depends on the level of competence perceived or claimed. Now if on read the various posts posted by someone they appear to hold themselves out a knowledgeable person in the subject they could easily be classes as a competent person and therefore be liable if something went wrong. Whereas yourself, about batteries is not likely to be classed as a competent person and thus be liable if something went wrong. Thus some care has to be taken in replies to questions.

 

BTW some of what you call the I think you would call the cheap end of the market do fair better on different charging etc regimes.

 

Your last paragraph is an interesting question, I do not know how your the starter and domestic batteries are joined together after starting but I will for the answer to this question assume a voltage controlled relay of some sort. Absolutely technically they should not be, but for convenience a lot of people do it. But the important point is they are not discharged together that is when most of the damage is done in a mixed bank. It is a compromise.

When we bought our boat it had four batteries of three different types. Two open cell, two sealed but different from each other. I thought "They will have to come out soon" and lowered my offer to allow for a new set of batteries. That mismatched set lasted a further 3 years before I retired them. Nothing bad happened they just got tired. Once I had them out I measured the resting voltage separately and 3 of them were OK but the 4th was way down like 10V

I replaced them with a matched set.

What I take from this is while keeping batteries in matched sets is good practice, mixing types and old and new isn't necessarily a disaster. So while I wouldn't recommend putting new batteries with old without seeing the situation, it can be done. Would the heathier 3 have lasted longer without the dud, I don't know

 

Top Cat

 

I think I have said something very close to the highlighted bit, each situation has to be on its merits. As to the last sentence I suspect as I do you know the answer, or the probable answer, but none of us will ever know what would have happened with that bank as it is no more :)

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Now that depends on the level of competence perceived or claimed. Now if on read the various posts posted by someone they appear to hold themselves out a knowledgeable person in the subject they could easily be classes as a competent person and therefore be liable if something went wrong. Whereas yourself, about batteries is not likely to be classed as a competent person and thus be liable if something went wrong.

LOL

 

Thank you for at least putting my mid at rest on that one!

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Unfortunately each manufacturer's batteries are different, eg if you look up the charging requirements for a Trojan battery they are different to those of say a Yuasa battery. Put them in a bank together and one would be undercharged and the other overcharged or both undercharge etc and so on and there would soon be problems.

 

Please could you elaborate on that point?

 

In what way(s) do the charging requirements for a Trojan battery differ from the charging requirements for other lead acid batteries?

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I'd just like to say that I disagree with nearly everything Geo has posted on this thread, but since the thread is so smothered in it, I can't be bothered to pick out individual points. Again.

 

I was just intrigued how in a single alternator system you can possibly arrange that the starter battery and the domestic bank don't get joined directly together, which, apparently, "absolutely technically they should not be". smile.png

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I was just intrigued how in a single alternator system you can possibly arrange that the starter battery and the domestic bank don't get joined directly together, which, apparently, "absolutely technically they should not be". smile.png

 

Why do modern boat engines have twin alternators, rather than one which would be cheaper?

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All lead batteries have more or less the same chemistry, and open batteries have very very similar characteristics. The difference in charging requirements largely reflects the whims of the manufacturer rather than the battery itself. Having said that a Trojan is a much tougher thing than a cheapo leisure and subjecting a cheapo to loads of over-charging at 14.8volts will upset it a lot more than it upsets a Trojan. But then mixing cheapos and Trojans is not like mixing up a few cheapos.

 

The real bottom line is that batteries are implicit current sharing devices, if one is a little "thirsty" it will take more of its share of the charge current till it gets to the same voltage as its peers then all will be well. Exactly the same during discharge.

I can measure big charge current differences when I start to charge my collection of Trojans (of mixed age) but it soon all gets a lot more equal.

 

Some devices will share current, some won't, batteries do.

 

...............Dave

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Why do modern boat engines have twin alternators, rather than one which would be cheaper?

 

They come with a single alternator and the mariniser adds a second one because this is actually cheaper and easier than upgrading the existing alternator, and builds in a nice bit of redundancy too, and is a good marketing feature.

The standard alternator most likely has a single V belt and probably limited wrap, probably because it shares a belt with the water pump. The mariniser fits a second big jobbie with a polyV belt.

Another advantage is that the mariniser can fit higher voltage alternators, or we can fit alternator controllers, without "stressing" the engines own electrics which might just invalidate the warantee.

 

................Dave

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Exactly the same during discharge.

 

I do understand that during charging of batterie/banks in parallel, providing the voltage is regulated all the batteries/banks will charge by drawing current according to their internal resistance. So a single alternator/split charging set up, where two banks of batteries are connected together in parallel during charging isn't detrimental to the batteries.

 

But, batteries with different internal resistances and/or at different states of charge will become charged at different rates. So when charging stops, for whatever reason, they may have different states of charge at that point. Connecting two such banks of batteries together while there is no charging current will mean some current will flow between the banks discharging one, charging the other and wasting some energy in the process. Discharging a fully charged starter battery into a less than fully charged bank of domestic batteries probably isn't what you would want. That's why the split charge relay or diode only connects the two banks together during charging.

 

So, while there should be no problem of paralleling-up batteries of different ages/types during charging, there are reasons why it might not be optimal to have them connected permanently in the same battery bank. But they are second order considerations and it's not battery killer.

 

 

 

Why do modern boat engines have twin alternators, rather than one which would be cheaper?

 

 

Redundancy. A single failed alternator won't cripple the boat.

 

Reliability. With separate charging sources, a failed cell in one or other battery bank won't stop the other from charging.

 

Simplicity. Keeping the banks permanently isolated instead of relying on a split charge relay, diode or switch.

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As soon as I got in yesterday I took a reading of 12.12.

I then ran the engine for 5 hours and went to work.

I've just returned and taken a reading of 12.71.

Am running the engine again now.

 

Does this reveal anything or nothing?

Could it actually be close to fully charged? I'm imagining it's a case of waiting till tomorrow (I'll be at work tonight) and taking another reading?

Edited by hackenbush
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Was the 12.7 immediately after your return from work (ie had been standing for several hours) or when you started the engine again (ie with the engine running)

 

If the 12.7 was after several hours 'standing' with NOTHING going in or out (no fridge, no lights, no phone on charge) then the battery is virtually fully charged - BUT - this does not mean that it is back to 'as new' state.

 

You can have a battery which has lost 50% its capacity, and it will still charge to 12.7v, but you cannot take as much from it (in Amps)

 

You can have a 5 litre bucket and when new it hold 5 litres of water, if you fill it half full with mud, it is still a 5 litre bucket but it only holds 2.5 litres of water.

The 'mud' is the stuff in the battery that is produced as a result of undercharging & misuse.

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Was the 12.7 immediately after your return from work (ie had been standing for several hours) or when you started the engine again (ie with the engine running)

 

If the 12.7 was after several hours 'standing' with NOTHING going in or out (no fridge, no lights, no phone on charge) then the battery is virtually fully charged - BUT - this does not mean that it is back to 'as new' state.

 

You can have a battery which has lost 50% its capacity, and it will still charge to 12.7v, but you cannot take as much from it (in Amps)

 

You can have a 5 litre bucket and when new it hold 5 litres of water, if you fill it half full with mud, it is still a 5 litre bucket but it only holds 2.5 litres of water.

The 'mud' is the stuff in the battery that is produced as a result of undercharging & misuse.

It was a test taken immediately after work with absolutely no draw on battery.

Before the 5 hour charge I topped up with water from Halfords. I also ran the engine on quite high revs.

Whether I'm in the "mud" scenario is I'd imagine quite hard to gauge with the multimeter I have

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It was a test taken immediately after work with absolutely no draw on battery.

Before the 5 hour charge I topped up with water from Halfords. I also ran the engine on quite high revs.

Whether I'm in the "mud" scenario is I'd imagine quite hard to gauge with the multimeter I have

 

In that case it is a valid reading and indicated the battery is taking a charge and has taken virtually all it will take.

 

When you topped the battery up with water, was the water above the plates or below?

 

It is possible to get an idea of how much mud there is in the battery, but you need to know how much drain you are putting on the battery. You take a reading with no discharge, use the battery and workout how many amp hours you have used, and take another reading which tells you the level of charge etc. Not an easy process without something that counts amp hours, but it can be done.

Edited by Geo
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In that case it is a valid reading and indicated the battery is taking a charge and has taken virtually all it will take.

 

When you topped the battery up with water, was the water above the plates or below?

 

It is possible to get an idea of how much mud there is in the battery, but you need to know how much drain you are putting on the battery. You take a reading with no discharge, use the battery and workout how many amp hours you have used, and take another reading which tells you the level of charge etc. Not an easy process without something that counts amp hours, but it can be done.

 

The water was depleted but still above the plates.

And I get the logic of rough guaging the usage. I'll test that when I return tomorrow morning. Roughly how many amps should 2 LEDs be using?

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The water was depleted but still above the plates.

And I get the logic of rough guaging the usage. I'll test that when I return tomorrow morning. Roughly how many amps should 2 LEDs be using?

 

smile.png That depends on their wattage a quick idea of their ampage is W/V=A so one at 6 watts at 12 volts would be 1/2 Amp. That will be good enough for what you are doing. So ten hours of the two lamps above would be 10Ahs, not a lot in battery term but a starting point

Edited by Geo
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Two LEDS will use not a lot, probably 0.3 amp together, or 0.6 amp if they are really bright ones.

 

If you are only using LEDs and the usual occasional water pump etc then you can get by with not much battery at all. Things that "hurt" are things that are running for a long time, fridges or a Laptop that is always on are the battery eaters.

 

Almost all liveaboards have been through the "keeping the battery charged" trauma. Do you just want more electricity or are you the sort of person who is interested in this stuff and wants to understand it better? This is a serious question as it will (hopefully) influence the advice you are given here.

 

Some old Listers can be notoriously bad at charging batteries so this might need looking at urgently. Lots of hours of engine running to put almost nowt into batteries is a waste of diesel.

 

One problem is that most of the "experts" here have smart well equipped boats and although they might know a fair bit of theory (in some cases) their advice is based upon their own experience in their own boats. NickNoman has got a Hudson with very very advanced electrics, he's even got coffee machines and electric blankets. I am bit more lo tech but still have 6 Trojan batteries, two alternators, alternator controller, 240v Travelpower, Smartguage and shunt based current display. Its actually quite hard for us to give good advice to someone living on a low tech boat with a single battery and not able to spend £1000+ on batteries and instrumentation. Maybe we should start a new thread on low cost liveaboard electrics ideas????.

 

..............Dave

Edited by dmr
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Two LEDS will use not a lot, probably 0.3 amp together, or 0.6 amp if they are really bright ones.

 

If you are only using LEDs and the usual occasional water pump etc then you can get by with not much battery at all. Things that "hurt" are things that are running for a long time, fridges or a Laptop that is always on are the battery eaters.

 

Almost all liveaboards have been through the "keeping the battery charged" trauma. Do you just want more electricity are you you the sort of person who is interested in this stuff and wants to understand it better? This is a serious question as it will (hopefully) influence the advice you are given here.

 

Some old Listers can be notoriously bad at charging batteries so this might need looking at urgently. Lots of hours of engine running to put almost nowt into batteries is a waste of diesel.

 

One problem is that most of the "experts" here have smart well equipped boats and although they might know a fair bit of theory (in some cases) their advice is based upon their own experience in their own boats. NickNoman has got a Hudson with very very advanced electrics, he's even got coffee machines and electric blankets. I am bit more lo tech but still have 6 Trojan batteries, two alternators, alternator controller, 240v Travelpower, Smartguage and shunt based current display. Its actually quite hard for us to give good advice to someone living on a low tech boat with a single battery and not able to spend £1000+ on batteries and instrumentation. Maybe we should start a new thread on low cost liveaboard electrics ideas????.

 

..............Dave

Its not that many years ago boats would only had one battery charged by a dynamo. Gas light, a foot pump for water.

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Its not that many years ago boats would only had one battery charged by a dynamo. Gas light, a foot pump for water.

 

And probably, no phone charger, no computer charging, no TV, and definitely no fridge, freezer, washing machine, tumble drier, toaster, deep fat fryer, coffee machine or electric blankets.

 

That's how they 'managed' with a single battery

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One problem is that most of the "experts" here have smart well equipped boats and although they might know a fair bit of theory (in some cases) their advice is based upon their own experience in their own boats. NickNoman has got a Hudson with very very advanced electrics, he's even got coffee machines and electric blankets. I am bit more lo tech but still have 6 Trojan batteries, two alternators, alternator controller, 240v Travelpower, Smartguage and shunt based current display. Its actually quite hard for us to give good advice to someone living on a low tech boat with a single battery and not able to spend £1000+ on batteries and instrumentation. Maybe we should start a new thread on low cost liveaboard electrics ideas????.

 

..............Dave

 

lol The luxury, I must be getting old and poor, lol. My NB had two 110s + starter a Lister HR2 and a single alternator. My present two boats have two alternators, one on each engine and battery monitoring BMV. But that is 10 years on. :)

 

And probably, no phone charger, no computer charging, no TV, and definitely no fridge, freezer, washing machine, tumble drier, toaster, deep fat fryer, coffee machine or electric blankets.

 

That's how they 'managed' with a single battery

 

and that is how I would guess hackenbush is managing, basic simple living. I could be wrong :)

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