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Big COL

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That's my understanding as well.

 

You can join differing AH batteries in parallel, but in series they need to be the same AH, and preferably batteries from the same supplier. It's an internal resistance thing, any differences in series will unbalance the charge/discharge rates across the set.

 

So if you've got these batteries set up for a 24v system I would expect the two reds in series, the two yellow in series and the two pairs then joined in parallel.

 

If it's only 12v, then it shouldn't make any difference, and you've either got dodgy batteries, or the red ones are starter batteries and can't handle life in a domestic bank.

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Richard.

 

According to my Lucas Marine book, charging should be at a 10 hour rate except in rare circumstances. In other words a 100 amp hour battery should not be charged at more than 14 amps, a 500 a/h bank at 70 amps and so on.

 

The calculation for the 500 a/h is.

 

500 divided by 10 multiplied by 1.4 = 70 amps maximum charge

(Factor for the afficiency of battery is 1.4 or 70%)

 

Presumably the max charge rate for mixed batt. sizes the calculation for the smaller one should be used.

 

The battery's internal resistance will determine what what charge it takes thats why all the batts. should be of similar size. I'm not sure that I would like to put 100 and 200 a/h batteries together

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From what I've read, you would take the full capacity, so for 300A/h (200A/h + 100A/h) you'd charge at 30A. It's as though the battery was contained in one large cell.

 

Of course I can also find info that says the opposite.

 

Personally I'd always make sure that all the batteries are of the same size/type/manufacturer. That removes one level of doubt, leaving only a couple of hundred to go.

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Khaffra / Big Col

 

Yes you can buy handheld clamp-meters, they simply clamp around a conductor and will display the current flowing through it. Direct current types are not common and they are quite expensive. I have had mine 5 years or so, it cost about £100. Can't remember where I bought it. There are several listed in the RS catalogue. The cheaper ones:

 

388-6706 .... £98 - 00

243-0661 .....£115 - 00

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Amicas that is the sort of thing you need but the ranges of 200 and 1200A DC are a bit high,

you would be better off with a 40A and 400A range that quite a few have, only thing to remember when using them on DC is to zero them first (normally a thumb wheel on them).

The one I have is a Heme LH410

 

They work by using Hall effect sensing

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I have two clamp on ammeters, one measures up to 75A which I normally leave on the alternator lead, and the other is 30A which I leave on the invertor lead (it does get hammered occaisionally).

 

They are both available from Vehicle Wiring Products

 

http://www.vehicle-wiring-products.co.uk/V...ers/meters.html

 

under Induction Ammeters.

 

They do not work by magic, they merely pickup the field generated by current flowing in the wire.

 

They are not very accurate and are prone to picking up currents from nearby wires or fields from magnetised objects. So sometimes you clamp it onto a wire which you know is not carrying any current, and it will give a reading. However by choosing a different point to clamp onto you can usually get round this.

 

And they are cheap.

 

Phil

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Philip.

 

I think you are confusing 2 different things, what you have are induction ammeters, as the name suggests the somehow pick up an induced field from the wire.

 

What I was refering to is a proper clamp meter which has a pair of jaws which must encircle the conductor, they use the hall effect principle and magic. See the Maplins link and the RS references.

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It doesn't work for DC that's why you need a hall effect sensor.

 

Hall was a nice man who noticed that a current flowing through a conductor in a magnetic field will produce a potential difference across the conductor.

 

So unlike the secondary winding type, a hall effect meter uses a voltage induced by the conductor in the magnetic field caused by the current flow in the wire your measuring.

 

Welcome to John O's world of magic.

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Phil what you have is a very basic current measuring device where you can get all sorts of errors caused by magnetic fields in the area you are using it and normally you can vary the readings just by moving it round on the wire.

Early AC Clampmeters had the same fault with you being able to vary its readings by moving it round the conductor or the position the cable goes through the clamp.

Modern Clampmeters using Hall effect devices are much more accurate and reliable with the readings they give, most have a spec of around 1% to 2% and moving the clampmeter around the conductor has minimal effect, another option if you already have a Digital Multimeter is to buy a clamp adaptor that is the same as a clampmeter but outputs mV into your DMM this can work out a bit cheaper.

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John

 

Did some googling on DC ammeters and the Hall effect, very interesting. Also read about what you're describing as induction ammeters,the consensus of opinion is that they get as close to being a measuring instrument as does a chocolate tea pot.

 

Colin

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Philip.

 

I think you are confusing 2 different things, what you have are induction ammeters, as the name suggests the somehow pick up an induced field from the wire.

 

What I was refering to is a proper clamp meter which has a pair of jaws which must encircle the conductor, they use the hall effect principle and magic.  See the Maplins link and the RS references.

 

I am not confusing them, but if I am confusing other people then I am sorry.

I was merely pointing out a cheaper, if less accurate alternative then those being mentioned.

 

And as for people who don't believe that they work on DC, I give up.

 

I remember now why I don't normally get involved on these discussion forums.

 

Phil

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Colin.

 

I didn't describe them as such, they are detailed in the Automotive Products site that Philip kindly drew our attention to. I have seen people using these, they are ok for checking for an output from your alternator but I don't think they pretend to be state of the art kit.

 

In fact the clamp meters are not brilliant, they can give a very jumpy reading sometimes.

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I am not confusing them, but if I am confusing other people then I am sorry.

I was merely pointing out a cheaper, if less accurate alternative then those being mentioned.

 

And as for people who don't believe that they work on DC, I give up.

 

I remember now why I don't normally get involved on these discussion forums.

 

Phil

 

 

Whoops.

Chill out Phil and welcome to the forum, its only friendly banter. Sorry if you felt insulted, but theres a good bunch on this forum. Stick with it.

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A quick tip if using a clampmeter on low currents or the lower part of the meters range where they tend to lose accuracy is to wrap the wire round the clamp several times this will increase the readings by the amount of times you wrap the wire round and give you more accurate results.

I know this is not possible with the likes of battery cables but it is unlikely you would be measuring low currents on that sort of cable.

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Khaffra / Big Col

 

Yes you can buy handheld clamp-meters, they simply clamp around a conductor and will display the current flowing through it.  Direct current types are not common and they are quite expensive.  I have had mine 5 years or so, it cost about £100.  Can't remember where I bought it. There are several listed in the RS catalogue. The cheaper ones:

 

388-6706 .... £98 - 00

243-0661 .....£115 - 00

 

There is a cheaper, if fiddly, alternative to expensive ammeters & shunts - calibrate an existing cable to use as a shunt. In future you will be able to measure current without breaking a circuit & measure currents larger than the capacity of your meter.

 

If you can't borrow an accurate, high current ammeter you need a DVM with at least a 5 or 10A range & preferably a second DVM to measure mV. Make sure everything is switched off. Connect the 10A DVM in series with a load - I remove a fuse or trip a CB then connect across it. Connect the mV DVM to the ends of a cable you want to measure current in - if it does not read zero you have a load connected. Do not include any terminal, switch or relay contact resistances.

 

Switch on devices in the (10A) monitored circuit e.g. tunnel light (typically 55w=4.5A or so). Take care, the 10A meter connection may be unfused! Note the readings on each meter & calculate the factor Amps/mVolt. In future you can measure any level of current in that cable to a reasonable degree of accuracy.

 

Lower currents will tend to read lower, larger currents higher than actual especially if the cable is undersized.

 

e.g. With only the tunnel light on I measured 8.93A (two tunnel lamps) across the removed fuse position & 15.40 mV across the cable feeding the service batteries - factor = 0.58. Now I can check the charge rate for the service batteries. e.g. I measure 55mV across the 'calibrated' cable, multiply by 0.58 = ~32A.

 

For your homework: 'Describe a method for calibrating the lead from the alternator to the first battery'. Marks will be awarded for originality.

Hint: connect a temporary load, e.g. lead-lamp, at the alternator.

 

 

Alan - (I am not a technical author - hope you grasped the idea)

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Quite a clever cheap idea, but accuracy will be somewhat limited as the resistance of normal wire changes with heat produced from passing a current, If you want high accuracy get some manganin and make a shunt and put that in series with your wire and measure the mV across that, the resistance of manganin is extremely consistent with temperature so can be calibrated at say 10 amps but will still give accurate reading at a higher current.

I like your idea though and for approx readings is ideal.

Still like the clampmeter as it can be swapped between different wires quickly and easily and can be used on other vehicles etc without being part of the boat.

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