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Timx

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When I started my career in 1972 I was allocated to the power maintenence team, where I was responsible for charging the main batteries for telephone exchanges in the area.

 

We charged to specific gravity, as well as measuring the tail curent every 30 minutes towards the end date of a charge. When it had remained constant for two 30 minutes periods the batteries were considered charged.

 

Also it was not unusual for the specific gravity to rise by another point after charging ceased. I believe this was due to the battery gassing ceasing when the charge stopped.

 

I was also familiar with one old installation where two batteries were used on a charge/discharge principle (one battery being connected to the load whilst one the other was charged from a motor generator set and then left to rest until needed. I cant remember to what level the load battery was discharged to, but it wasnt much. Changeover and charging took place twice per week. These batteries must have been 20 years old then, so this regime must have been kind to batteries.

 

So the guy did have a point, mind you for my place that would have meant a load more batteries. I don't think being a commercial Co the bosses would have bought it that long term. However I wonder what the cost relationships would be to have two domestic banks on a boat. Must give that some thought

Tail current measurement is far from 'something invented by boaters', it's been an accepted practice for years. The Battery faq mentions it as a method and I seem to recall that Trojan even list it as one method of determining 'full' charge.

 

It's also how the majority of chargers determine when to switch to float.

 

 

Good I am glad it has been around a while because I have used it for a far time. My head is full of other things at the moments rather than trying to remember when that came in to use.

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I was also familiar with one old installation where two batteries were used on a charge/discharge principle (one battery being connected to the load whilst one the other was charged from a motor generator set and then left to rest until needed. I cant remember to what level the load battery was discharged to, but it wasnt much. Changeover and charging took place twice per week. These batteries must have been 20 years old then, so this regime must have been kind to batteries.

We had the same system for driving the standby Navigation Lights and the fog horn

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So what exactly is your definition of 100%? In other words, under what conditions should it read 100%?

 

It sounds like you think I'm criticising the Smartgauge, but I may be wrong?

 

I'm definitely not criticising the Smartgauge, merely pointing out a limitation of the device, which is readily accepted by the makers, and which might be missed by some users:

 

My point is that, if a boater who isn't particularly technical uses a Smartgauge as a simple fuel gauge for batteries, and has no other means of monitoring, he/she would naturally feel happy to cease charging when the Smartgauge shows 100%. In reality, the batteries would probably only be charged to 90%, and we all now know that regularly charging your batteries to only 90% will result in loss of capacity, possibly quite quickly.

 

It is a downside that Smartgauge readily admit, and they warn about it in the instruction book, (but some might miss it as it's all quite small print, and many buy one because it's purported to be a simple fit and an easy to read battery fuel guage).

 

 

When charging my batteries, (4 x Trojan T105), the Smartgauge shows 100% long before the batteries are drawing what might be called a tail current, (4A or so in my case). In fact, on Sunday, when the Smartgauge reached 100%, the batteries were still drawing 20A.

 

I agree that, if I stop charging, and use the batteries for a while with a load, the Smartgauge will sort itself out - but that's not a very convenient test when charging before going home on a Sunday - which is why I have a NASA BM2, which gives Amps drawn, amongst the other stuff.

 

Having said all that, this thread has gone well beyond being of any assistance to the OP, so I hope he got the help he needed before it degenerated into the depths it seems to have reached :(

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He did Richard, he is replacing the batteries with like for like (AGMs) and buying a smartgauge. Has has asked for advice on which AGMs to buy and we are awaiting details of exactly which batteries are fitted at the moment, manufacturer and model etc.

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... cease charging when the Smartgauge shows 100%. In reality, the batteries would probably only be charged to 90%, and we all now know that regularly charging your batteries to only 90% will result in loss of capacity, possibly quite quickly.

 

I think you are wrong to say "probably". "Possibly" I will agree with. However in my experience the batteries are adequately charged when the SG reaches 100%.

 

When charging my batteries, (4 x Trojan T105), the Smartgauge shows 100% long before the batteries are drawing what might be called a tail current, (4A or so in my case). In fact, on Sunday, when the Smartgauge reached 100%, the batteries were still drawing 20A.

 

Couple of points here, firstly 20A is a lot I'll agree, however it is only just over 4% and if you installed a Victron BMV monitor that would reset to 100% out of the box at 4%. So presumably Victron considers just under 20A to be fully charged. I don't happen to agree with them but my point is that different people have different ideas of what 100% charged is and, if I may use my favourite phrase again, since a battery can never really be fully charged - that state can only be asymptotically approached - it will always be a compromise as to when to stop charging with no right answer, only personal choice.

 

Secondly, how do you charge your batteries (ie what maximum current)? I ask because I do find the tail current is around 1.5% when our SG reaches 100% but we do charge the batteries fast with the 175A alternator and perhaps, if your max current is much lower, that is why we get a lower tail current at 100% than you do (the SG working by means of some voltage x time integrating algorithm).

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I think you are wrong to say "probably". "Possibly" I will agree with. However in my experience the batteries are adequately charged when the SG reaches 100%.

 

 

Couple of points here, firstly 20A is a lot I'll agree, however it is only just over 4% and if you installed a Victron BMV monitor that would reset to 100% out of the box at 4%. So presumably Victron considers just under 20A to be fully charged. I don't happen to agree with them but my point is that different people have different ideas of what 100% charged is and, if I may use my favourite phrase again, since a battery can never really be fully charged - that state can only be asymptotically approached - it will always be a compromise as to when to stop charging with no right answer, only personal choice.

 

Secondly, how do you charge your batteries (ie what maximum current)? I ask because I do find the tail current is around 1.5% when our SG reaches 100% but we do charge the batteries fast with the 175A alternator and perhaps, if your max current is much lower, that is why we get a lower tail current at 100% than you do (the SG working by means of some voltage x time integrating algorithm).

 

I believe you have an Amp/hour device and read tail current from it to decide full charge and do not rely solely on a smartgauge if at all for the end of charge, rather you rely on the tail current displayed by your Ah device.

 

The BMV is not meant to be used straight out of the box and comes with a detailed manual to assist with the setup. It even details how to calculate Peukert’s exponent for the owner's particular set of batteries. The tail current setting is adjustable from 0.5A to 10A and its setting depends on the size of the battery bank, just as the owner would calculate it if using an ammeter except he/she has only to calculate it once.

 

Regarding probably/possibly as used in your post, from my experience it is probably.

 

As to fully charged, technically that occurs when all the sulphuric acid is returned to the electrolyte. I am surprise you seem to dispute that this situation exists. What you might do or suggest to others to save money at the cost of the battery life is a different thing. But please do not blame the batteries, once all the sulphuric is recovered the battery will be at its maximum charge level. Anything else and the battery is not fully charged to its full capacity and on the way to being sulphated and gradual failure.

 

The smartgauge has a place, but I do not believe it right that it should be pushed, as you seem to do ignoring its manufacturer's acknowledge failings or trying to give the impression they are less than they are. The owners however technically inept or experienced need to know those failings and not believe that it is perfect. Nothing unfortunately in battery monitoring in the leisure boating world is perfect, money does not allow it.

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Nobody here has posted that SmartGauge is perfect. Everyone here has posted that it has failings.

 

So why do you clutter up threads in this manner, repeatedly pointing out what we all already know?

 

Could it be in days gone by he tried it on Gibbo and got slapped down for his trouble? If so it would have been in no uncertain terms.

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Could it be in days gone by he tried it on Gibbo and got slapped down for his trouble? If so it would have been in no uncertain terms.

Could well be, Tony. Whatever the case he does seem to feel a need to clutter threads up with post after post of irrelevant information.

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When i look at treads i can sort of guess who speaks from experience and those that answer from google with all the technical facts and figures that few could ever remember or now about .but that info can be wrong or misguided which is easily found out when you are researching a sibject.just saying .

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When i look at treads i can sort of guess who speaks from experience and those that answer from google with all the technical facts and figures that few could ever remember or now about .but that info can be wrong or misguided which is easily found out when you are researching a sibject.just saying .

I beg to differ ;-) There are plenty of knowledgeable people who post and back up their suggestions with a link. Some will quote some webpage because they were fact-checking or refreshing their memory. It also pre-empts those who always ask for evidence of one's opinions.

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When i look at treads i can sort of guess who speaks from experience and those that answer from google with all the technical facts and figures that few could ever remember or now about .but that info can be wrong or misguided which is easily found out when you are researching a sibject.just saying .

Damn.

Looks like I've been rumbled.

But seriously, I don't see that there's anything wrong with doing a bit of Googling on behalf of someone else (who may be stuck in the middle of nowhere with a slow connection and a small screen).

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I could google answers to a lot of posts but i would have no experence to back it up or filter the errors,i didnt put my post very well so i will shut up

Your point was valid in some cases, I just don't think it holds for the majority. Don't worry we always debate every opinion here!

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I could google answers to a lot of posts but i would have no experence to back it up or filter the errors,i didnt put my post very well so i will shut up

 

No, don't shut up. Everyone's inputs are valid until more than one well informed people who agree say differently. At that point in might be wise to shut up unless you know on firm grounds that you are correct.

 

 

When i look at treads i can sort of guess who speaks from experience and those that answer from google with all the technical facts and figures that few could ever remember or now about .but that info can be wrong or misguided which is easily found out when you are researching a sibject.just saying .

 

This can be a bit deceptive. I occasionally lock horns with someone who, in this thread I agree with and the detail of their posts can, at times, give the impression that they are very theory driven and maybe a Google warrior. However although I do not think this particular person's careerer involved much experience of what they post on I do think they have done much research and almost always come up with absolutely correct answers. Where we disagree it is usually because they want things absolutely 100% correct while I will settle for 90% correct AS LONG as that 90% helps people not so into a topic understand the main points better. This is not a criticism of anyone, I am just pointing out that it can be very hard to sort out the Google warriors from those with lost of experience to back up theory work.

 

 

FWIW the way this and other topics have gone I suggested to Dan that it might be an idea to appoint some technical adjudicators so there was a way of non-specialist moderators getting god advice as to when a thread should be locked or members warned. I feel it unfortunate that he feels it unnecessary because it is a "discussion forum". While that is true it is also true that members often seem to post on the basis of just their experience on their boat rather than years of experience with theoretical backup. Such posters are on;y trying to be helpful but in all too many cases they just confuse the issues.

Edited by Tony Brooks
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<snip>

FWIW the way this and other topics have gone I suggested to Dan that it might be an idea to appoint some technical adjudicators so there was a way of non-specialist moderators getting god advice as to when a thread should be locked or members warned. <snip>

If only, Tony, if only...

biggrin.png

 

(edited to say that, for the avoidance of doubt, this post is intended to be read as "tongue-in-cheek".)

Edited by PaulG
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You obviously mean me. For the record I had a career as an electronic design engineer before I became a pilot and whilst yes that involves theory more than spannering, I slightly resent the accusation that I got everything from google! My feeling is that you might as well try to be 100% correct unless it seriously confuses the issue. Taking explanatory short cuts somtimes is a good thing, but sometimes stores up problems for the future. It could also be seen as a little patronising ie "I know the full facts but you are to stupid to understand so I'm only going to give you the simplified explanation (much as one would do to a small child)".

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Google doesn't necessarily have all of the answers, and often there is more than one way of solving a problem.

 

What I like about this forum is that someone has a problem, different people with differing g experiences answer it and also correct each other, so that in the end the best solution is arrived at. This weeds out the people with the incorrect answer and those with axes to grind.

 

Occasionally someone comes up with a new (to me) way of doing something, thus adding to my knowledge.

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Nick, I don't believe that Tony suggested that you did get everything from Google, rather the opposite. I suggest you read his post again smile.png

I was thinking of posting something about caps (the fitting and wearing thereof).

But in the interests of peace and harmony, I won't.

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I think that you have got hold of the wrong end of the stick.

 

I did have you in mind but please read what I said. I said that you could give the IMPRESSION that you were a Google warrior, not that you are one. Even if I did suspect you had no trade association with electrics I have seen enough of your post to know that you are very well versed in the subject and are willing to experiment if required to get an answer.

 

If I wanted a detailed discussion on many electrical topics you would be well up my list of preference. I am not so sure if I wanted a fast practical solution though but that is in no way denigrating you.

 

If anything I was trying to pre-empt fall out from Mickp's post because I think that you do sometimes come across like that.

 

We will just have to differ on our views of how bets to help people though.

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My Take on how to read a Smart Gauge.

 

Battery takes a long time to run down-- takes a long time to charge = all good.

 

Battery takes a short time to run down-- takes a long time to charge = heavy drain on battery. (using to much power)

 

Battery takes a short time to run down -- takes a short time to charge = battery has reduced capacity. (battery at end of life, needs replacing)

 

Smart Gauges tell it as it is, you may not like what they say, but are almost unknown to be wrong.

 

It won't tell you if, only 1 battery in a bank is duff, only that the bank has a problem.

 

A hydrometer is the only way of checking each cell in each battery. (assuming Wet Lead Acid battery)

 

My two-pennies worth!

 

Bod

Edited by Bod
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