Multimeters and other things.

[Gibbo]

 

Read post #1 in this thread.

 

Then read my post.

 

Now explain what is off topic.

 

Or did you not actually read post #1 ?

 

Gibbo

[awatsonbcp]

seem to have strayed from the original topic a bit?

 

my multimeter was bought in Maplin last year and has just paid for itself by highlighting a broken battery switch which was causing various things to behave oddly.I just worked around the cicuits until I found the point where 12 volts stopped and 0 volts started.Saved a costly visit to the boatyard at £30 an hour

[DHutch]

The point made about the accuracy of meters was made *purely* with regard to their purpose for determining state of charge. Not for any other purpose.

- And for the purpose of attempting to determine state of charge, a meter with less than 0.5% accuracy is a complete and utter waste of time.

I think thats the nub of it.

- A cheap meter is a dam useful tool.

- I have a £20 skytronic unit that i use/abuse all the time, and its very usefull indeed. Even with on segment of display non-functioning.

 

However, the point the other thread raised, was, as said here, that this quality of meter (while fine for many other jobs onbaord) is no upto giving anything more the than a fingar-waving idea of state of charge. And that for £40/50 a second hand fluke unit can be purchased, which would be far more suitable.

 

 

 

Daniel

[carlt]

Read post #1 in this thread.

 

Then read my post.

 

Now explain what is off topic.

 

Or did you not actually read post #1 ?

 

Gibbo

The point (I believe) John was making was that the scientific claptrap that you write may be factually correct but is just garbled nonsense to anyone who hasn't studied maths to degree level or higher. I don't think he was trying to reopen a very tired and quite frankly pointless debate.

[Gibbo]

The point (I believe) John was making was that the scientific claptrap that you write may be factually correct but is just garbled nonsense to anyone who hasn't studied maths to degree level or higher. I don't think he was trying to reopen a very tired and quite frankly pointless debate.

 

The point John made was that an expensive and accurate meter was not required. The point Chris made in response was that in order to ascertain the state of charge of the batteries an expensive and accurate meter *is* required. I reiterated what Chris said because he was correct and John was not.

 

The original thread was started by Theo and *specifically* mentioned using the meter to ascertain state of charge. It is therefore pointless trying to pretend that the thread veered OT.

 

I have never written "claptrap" that requires a degree to understand. I specifically avoid doing so. This isn't the correct place for it.

 

Gibbo

[Supermalc]

Nick asked.....

 

I am certain that someone with much more practical experience than me will be able to point out the important features that I need to consider.

 

I have already found from a previous thread that I need a 0.1V resolution if it is to be useful in determining the charge state of my batteries.

 

Now as I have already said, the answer that should have been given was to buy a cheap multimeter for use around the boat, and a dedicated voltmeter permenantly installed and wired to determine the state of the batteries.

 

I suppose it is a 'fluke' you answered as you did. I've never even heard of one before. I do have a 'Multiminor AVO'. In the 80s when digital meters became the fashion, a friend who worked in the home office police and fire radio devision, got some 'broken' from the surplus shop. They had ended up there as the 'workers' wanting to be fashionable had 'accidently' dropped their meter, to get a new one. What actually happened is the needle spindle jumed out. A simple 10second job 'mended' them.

 

It appears the 'Rolls Royce Syndrome' has struck again........

[carlt]

The original thread was started by Theo and *specifically* mentioned using the meter to ascertain state of charge. It is therefore pointless trying to pretend that the thread veered OT.

 

I have never written "claptrap" that requires a degree to understand. I specifically avoid doing so. This isn't the correct place for it.

 

Gibbo

Ok Gibbo, two points.

First I wasn't referring Theo's thread, I was referring to this one.

 

Second: I've just read every one of your 399 posts on this forum (if someone tells me I'm wrong, I just need to know, one way or another) and I can say that, in my opinion, you haven't posted anything which requires more than an O level (that's gcse youngsters) in maths except one or two which are approaching A level standard. Many of your posts I can see you sagely rubbing your chin at chris w's over complicated stuff, though, but you haven't joined in.

 

So, could you waste post 400 accepting my apology please?

[chris w]

Gibbo

 

Hey buddy - don't bother telling them again; if they blow themselves up or damage their equipment, it's not our fault. As the saying goes, "Ignorance is bliss". There must be some very happy folks on here!

 

Some folk seem to forget that, only a week or so ago, out of our O level maths dropped a very simple formula to allow them to measure the state of charge of their batteries at any time from taking 3 simple voltage measurements (assuming they have an appropriately accurate meter of course)!

 

Chris

Edited March 12, 2007 by chris w

[carlt]

Gibbo

 

Hey buddy - don't bother telling them again; if they blow themselves up or damage their equipment, it's not our fault. As the saying goes, "Ignorance is bliss". There must be some very happy folks on here!

 

Chris

How can you blow yourself up with an undercharged battery?

[chris w]

Short it out and find out just how not "undercharged" it is.

 

Chris

[Supermalc]

going to be used to see if a wire has 12 volts on it or not, then a test lamp is cheaper, easier to use and less likely to confuse anyone.

 

Gibbo

 

If by test lamp you mean a bulb in a holder, and two wires, well I disagree it is easier to use. If you are trying to find continuity in a wire, or circuit, you have to attach a wire to a battery to one end, and the wire of the test bulb to the other, before attaching the other wire to the test lamp to the battery.

 

It's why I paid a tenner for a meter......to save me having to fiddle around trying to hold several wires on my own.

[carlt]

Short it out and find out just how not "undercharged" it is.

 

Chris

Ok, but what relevance that is to anything escapes me.

[chris w]

Ok, but what relevance that is to anything escapes me.

 

 

I rest my case

 

Chris

 

If by test lamp you mean a bulb in a holder, and two wires, well I disagree it is easier to use. If you are trying to find continuity in a wire, or circuit, you have to attach a wire to a battery to one end, and the wire of the test bulb to the other, before attaching the other wire to the test lamp to the battery.

 

It's why I paid a tenner for a meter......to save me having to fiddle around trying to hold several wires on my own.

 

No, he doesn't mean that. For about £3.99 you can buy a "12v screwdriver" which doesn't need to be clipped to anything. It will detect mains and/or 12v (and indeed other voltages in between these) just by touching its tip on a terminal. Maplin were throwing them in free a few weeks ago with every order.

 

Chris

Edited March 12, 2007 by chris w

[carlt]

deleted because I just can't be bothered.

Edited March 12, 2007 by carlt

[Supermalc]

Short it out and find out just how not "undercharged" it is.

 

Chris

 

Have you been drinking Chris? Do you realize that is a very dangerous comment to make on an open forum, where young, or inexperienced people may be reading.

 

Shorting a battery out can be VERY DANGEROUS, as you should know. The hydrogen can be ignited by a spark, causing the battery to blow up, possibly covering you with acid.

 

I had occasion to witness just such an event a couple of years ago. There were a few boats around as it was a bank holiday, and a small cruiser was locking through with a few other boats. I noticed they had pulled their boat out of the lock, yet they had driven in. The boat was fitted with a 15hp Honda outboard.

 

I walked round to see if they needed any help, and I carry a selection of tools etc. on my boat. Just as I was standing on the keyside, the battery blew up when the man tried to start the engine.

 

It turned out they had bought a new battery the year before, but had misunderstood thinking it was one that didn't require checking to see if the electrolyte was low and water needed to be added. I believe she had been told this was so.

 

The battery had in fact run dry, and the plates had sparked inside. It had blown the plastic battery case apart as well. Luckily there was very little acid, and so was soon cleaned up, but had the man been leaning over the battery, or it had contained a little more acid, I would certainly have been taking him to hospital.

 

The outboard could be pull started, and didn't have to have a battery connected, so they could continue to Boston, where they could buy a new one, thankfully not spoiling their holiday.

[chris w]

Just because I won't get into a p***ing contest with you chris doesn't make me more ignorant than you, just less pathetic.

 

Ah, here come the insults - "the last refuge of a scoundrel" to misquote Samuel Johnson.

 

In terms of electrics/electronics, at least, you are clearly more ignorant. If you don't want my advice I suggest you simply ignore it. It's free so you have nothing to lose (except maybe your life if you have an electrical accident).

 

Chris

Edited March 12, 2007 by chris w

[Supermalc]

I rest my case

 

Chris

No, he doesn't mean that. For about £3.99 you can buy a "12v screwdriver" which doesn't need to be clipped to anything. It will detect mains and/or 12v (and indeed other voltages in between these) just by touching its tip on a terminal. Maplin were throwing them in free a few weeks ago with every order.

 

Chris

 

But you still can't do a continuity test with one of these unless you attach a battery to the other end....assuming there is no power of course.

[chris w]

But you still can't do a continuity test with one of these unless you attach a battery to the other end....assuming there is no power of course.

 

That's true of course which is why a meter is sometimes useful. You still need 2 hands to use the meter though.

 

Let's say a light is not working. If you do have the boat battery connected then to check out say the continuity of the switch using the "screwdriver" thingy you simply close the switch and touch it either side of the switch. Clearly if the switch is OK, you will detect 12v on both sides of it. If you then check the terminal on the lamp connected to this switch and there is no 12v then you know the issue lies on the intervening cable or on the terminal itself. A one-handed job.

 

All test equipment has a use. You should have a meter - but sometimes some tests are easier using something else. And if you are going to buy a meter, then at least get one accurate enough to measure battery state-of-charge which is a critical measurement on a boat.

 

Chris

[carlt]

Ah, here come the insults - "the last refuge of a scoundrel" to misquote Samuel Johnson.

 

In terms of electrics/electronics, at least, you are clearly more ignorant. If you don't want my advice I suggest you simply ignore it. It's free so you have nothing to lose (except maybe your life if you have an electrical accident).

 

Chris

In terms of electrics/electronics, at least, you have no idea about my background, as to the insult you'll note I deleted it 4 minutes before your post. Like I said Chris, I've got nothing to prove to you, or anyone for that matter. I am confident enough of my electrical knowledge to judge your pontificating. But note one thing chris, I have never disagreed with your theories, I just think you are more interested in proving how much cleverer you are than everyone else, rather than advising them, otherwise you would (like Gibbo) keep your maths to a level less technically minded people can understand.

[chris w]

Have you been drinking Chris? Do you realize that is a very dangerous comment to make on an open forum, where young, or inexperienced people may be reading.

 

It's called ironic humour

 

Chris

 

otherwise you would keep your maths to a level less technically minded people can understand.

 

My maths is not directed at people that don't understand it. When it occurs, there is usually an exchange of mathematical ideas between a few people who do understand it and usually out drops a simple formula or methodology which hopefully everyone can use or from which they can benefit. It's not practical to PM four other people off-line all the time. It's just maths, it's not black-magic; I think you underestimate the level of education and/or interest on this forum.

 

Chris

[Supermalc]

That's true of course which is why a meter is sometimes useful. You still need 2 hands to use the meter though.

 

Let's say a light is not working. If you do have the boat battery connected then to check out say the continuity of the switch using the "screwdriver" thingy you simply close the switch and touch it either side of the switch. Clearly if the switch is OK, you will detect 12v on both sides of it. If you then check the terminal on the lamp connected to this switch and there is no 12v then you know the issue lies on the intervening cable or on the terminal itself. A one-handed job.

 

Agreed Chris, but why carry 2 tools when one will do.

 

And if you are going to buy a meter, then at least get one accurate enough to measure battery state-of-charge which is a critical measurement on a boat.

 

Sorry, but I strongly dissagree with you on this. The only reason I need charged batteries is to start the engine. I just turn the key and the engine either turns over, or it doesn't. A simple test, which will tell you if the batteries are charged, or not.

Chris

 

Btw I am really, really NOT trying to argue, or anything. I'm just trying to point out you might? have misunderstood what is required.

 

Also of course ...... entertain the punters reading the forum

 

 

It's called ironic humour

 

Chris

 

I know........so's mine but with a ring of truth.

[chris w]

Sorry, but I strongly dissagree with you on this. The only reason I need charged batteries is to start the engine. I just turn the key and the engine either turns over, or it doesn't. A simple test, which will tell you if the batteries are charged, or not.

 

Well, that's one sure test I guess

 

Chris

[smileypete]

Hi,

 

I reckon that with older batteries, using a DMM alone to determine state of charge from it's terminal voltage, however accurate, can be misleading.

 

A more useful (but less convenient) way is to use a hydrometer, and learn a little about how lead acid batteries work.

 

Once you have a little knowledge and experience, you'll know why the above statements make a lot of sense A good place to start would be to read the 'Car and Deep Cycle Battery FAQ' (search for it on the web).

 

 

BTW I have two different multimeters, one from Maplin which cost £2.50, the other off Ebay, which cost about... £2.50 too.

 

If worried about using an unfused meter, just wire an inline fuse holder into one of the probe leads, or find someone to do it for you. Simple!

 

cheers,

Pete.

[chris w]

I agree with you Pete about using a hydrometer - it's a very good way to determine charge state (given the usual advice about allowing the batteries time to stabilise after use etc). The only practical difficulty though is that the batteries are often stuffed up on the counter (certainly on a cruiser stern) and are almost inaccessible from a hydrometer standpoint, having no real free space above them.

 

Chris

[Gibbo]

Er...............

 

Just to confuse the issue, measuring the SG of a battery won't tell you the state of charge

 

It's true I'm afraid. And I'm laughing now as we head into another long thread

 

If a battery is down to say 80% of its original capacity (due to ageing) then measuring the SG when it's just been charged will show a reading of about 65% to 75% of the difference between 1.000 and the SG when it was new and fully charged. The exact figure depends upon what has caused the majority of the lost capacity, whether it be sulphation or plate shedding.

 

So if you take the SG reading and it shows say 1.255, yet when it was new it showed 1.270 one would conclude that the battery is not fully charged. But it is.

 

So unless you also know the condition of the battery, the SG won't tell you the state of charge. And whilst measuring the voltage can (after a long rest) show the state of charge, it won't show the battery condition. A fully charged, completely knackered battery, will show exactly the same voltage as it did when it was new and fully charged.

 

hehe

 

Gibbo

 

Ok Gibbo, two points.

First I wasn't referring Theo's thread, I was referring to this one.

 

I thought that first time I responded which is why I responded the way I did. My response was in no way OT with regard to the first post in this thread.

 

That first post contained the words "I can assure any-one that the accuracy is greater than is necessary for anything that will be needed on a boat ".

 

Note the word "anything"

 

Well.... I will assure anyone that the accuracy will *not* be greater than is necessary for...... etc

 

Second: I've just read every one of your 399 posts on this forum (if someone tells me I'm wrong, I just need to know, one way or another) and I can say that, in my opinion, you haven't posted anything which requires more than an O level (that's gcse youngsters) in maths except one or two which are approaching A level standard. Many of your posts I can see you sagely rubbing your chin at chris w's over complicated stuff, though, but you haven't joined in.

 

So, could you waste post 400 accepting my apology please?

 

Go on then

 

Gibbo