wiring in ammeters

The ammeter either needs to be in series with the main feed cable from the battery to the car and alternator so it sees the current going into and out of the battery but NOT the starter lead as that carries the saterter current at ~ 250A peak on a cold start. I.E. disconnect the alternator cable and cable(s) to the ignition switch at the starter and connect the ammeter across the gap... which means large cables into the cab which is not a problem as the ignition switch cable goes that way anyway and carries all the load to the vehicle . OR you need an ammeter with a shunt... this is a resistor whch goes in the same cable as above under the bonnet and then the ammeter reads the voltage drop across the resistor when the current flows and is in effect a volt meter calibrated in amps ...... A = V/R so they are linear for a fixed resistance. I this case you need smaller cables .... BUT if one of the meter cables goes to earth then the cable will evaprate as there is no fuse so beware it's not a safer option just a different way of doing it !!!! go with heavy wire and a normal ammeter ... get a + /- 60A or

80A for preference if you can as the Landy alternator can poke out that much if not more into a flat battery .... .

Whooo how did i get that much info on one page ..... those anti old gimmer pills must be working ... usually have troble with urgghh and ahhh these days ... Gromit

OK. That makes sense to me - so I could connect it in series between the alternator/main wiring loom feeds and the +VE feed.

OK. This also makes sense, but I cant seem to find any car places selling ammeters with seperate shunts, and they seem very expensive from the marine shops.

I already have a couple of ammeter guages (like this TIM one -

I presume that I would have to wire these upusing the first 'in series' method then?

Biggest wire i have is 30A or so i think. Stll not keen on bringing everything up through my dash though.

Ta!

On or around Thu, 15 Apr 2004 17:17:46 +0100, Tom Woods enlightened us thusly:

that's the normal way of doing it. Mostly, there's a sod-off wire from the battery + to the starter switch (solenoid) where sundry other wires also arrive. All these other wires have to be disconnected from the point where they are, and fed through the ammeter, back to the original point. Thus the ammeter is in series with *everything* except the starter.

YEP DISSCONNECT THE FEEDS FROM THE STARTER MOTOR AND CONNECT THEM TO THE NEW CABLE TO THE AMMETER OR SHUNT WITH A NUT AND BOLT AND INSULATE IT WELL WITH EITHER HEATSHRINK SLEEVING OR A RUBBER SLEEVE AND TIE WRAPS THEN TAKE ANOTHER CABLE FROM THE ORIGINAL TERMINAL TO THE OTHER SIDE OF THE AMMETER OR SHUNT.... IF YOU GET IT BACKWARDS THEN ALL THAT HAPPENS IS THAT THE METER READS + WHEN ITS DISCHARGING AND - WHEN ITS CHARGING SO SWAP THE LEADS OVER AT THE METER

istor when the current flows

YEP AGAIN .... THE SHUNTS ARE USUALLY A CALIBRATED BIT OF WIRE OR A PRINTED CIRCUIT ON THE DASHBOARD POD ..... IT IS ON A ROVER 3500 P6 WHICH I HAVE.WHICH BRINGS ME TO YOUR OTHER THING ABOUT CABLES INSIDE THE CAB

THAT GAUGE LOOKS IDEAL

I HOLE BIG RUBBER GROMMET AND SOME SUITABLE CABLE .... MAKE IT STRANDED NOT SOLID HOUSE STUFF AS THAT WILL FRACTURE WITH THE VIBRATION .... CAN GET SUITABLE CABLE AT HALFORDS OR CAR PARTS DEALERS USUALLY BY THE METER..... THE IGNITION CABLE ALREADY IS THIS FEED AS THE FUSE BOX IS UNDER THE STEERING WHEEL THE CABLE FROM THE STARTER TO THE SWITCH IS UNFUSED AND HASN'T GONE BANG YET .... I HOPE

OK. looks like i'll have to stick it in in series then. Would prefer one with a shunt, but that would seem to involve lots of money!

Voltmeters sound a lot easier. Does the battery voltage give you a fairly accurate idea of how well the battery is charging? From when ive messed about in the past, if a battery is charging it reads about

14V, otherwise it stays at 12. That about right?

How much does the battery voltage drop before you would have trouble starting the car? Is there an obvious drop?

Ammeters have gone out of fashion with the introduction of alternators and their higher charging currents, for just the reasons you are seeing. If you really want to fit one, a shunt meter is the way to go, with both leads fused, but as you have found, they are a lot more expensive.

That sounds about right, although how low it goes depends on the state of the battery and how much load is on it when the engine is not running - e.g. lights. A voltmeter shows the state of the battery more directly than an ammeter, rather than the amount of charge going in. One point to note is that if the voltmeter is earthed to the chassis, and you have a poor earth between the chassis and the engine, you can expect some strange readings.

There will be an obvious drop, although how low a voltage will stop it from starting depends on the engine type, its condition, and how the battery stands up to the starter current. As an example, with the battery good, my

2.25 petrol will start reliably with the battery discharged to 10v, but will not start with the battery at 12v when the battery is on its last legs, or at 11v when it needs new points with a good battery. JD

On or around Thu, 15 Apr 2004 20:14:18 +0100, Tom Woods enlightened us thusly:

we-ell... the normal output voltage of most modern alternators is about

14.5-15V, but of course the real question is whether the battery's charging. However, assuming the battery to be not-buggered, which you tend to notice anyway, a voltmeter will tell you whether the alternator's alive. if the voltage drops much below about 14V at revs, especially with the headlamps and blower and stuff on, then the alternator output is lower than it should be.

In fact, and ammeter doesn't tell you if the battery is actually charging, only that it's being supplied with current.

Twas Thu, 15 Apr 2004 19:51:01 +0100 when "Rubberboy" put finger to keyboard producing:

caps lock! it's over there on the left, press it would you?

-- Regards. Mark.(AKA, Mr.Nice.) ___________________________________________________________ "To know the character of a man, give him anonymity" - Mr.Nice.

mrniceATmrnice.me.uk 110 CSW 2.5(na)D___________________________________________________________

Twas Thu, 15 Apr 2004 20:14:18 +0100 when Tom Woods put finger to keyboard producing:

I've recently fitted a new 65A alternator and battery in my 110 (both were knackered when I bought it).

I've found my voltmeter (on the dash) to be ideal at monitoring battery state, turn the ignition on and if the needle makes it half way you can start the engine, it'll turn over with the needle alomst down to the red (diesel engine).

with the engine running the needle goes over to the right and shows there is pleanty voltage going to the battery from the alternator.

I was going to fit an ammeter but having muddled through alternator and battery trouble I've found the voltmeter tells me everything I need to know.

-- Regards. Mark.(AKA, Mr.Nice.) ___________________________________________________________ "To know the character of a man, give him anonymity" - Mr.Nice.

mrniceATmrnice.me.uk 110 CSW 2.5(na)D___________________________________________________________

Thats useful to know. Thanks. I think i'll forget the ammeter.

Has anybody seem any cheap digital voltmeters for sale?. Like the LCD screens you get in a multimeter? Stupidly, it seems that the cheapest way to do it may be to actually rip a multimeter apart. I bought 2 for £5 in the sale at maplins a few months back..

I wouldn't, since an ammeter and a voltmeter are telling you different things. Voltmeter is the best guide to the actual state of the battery, while the ammeter is the best way of knowing what the system is doing to it (in terms of charge/discharge).

Yuck! I've a rather old fashioned but working Smiths Voltmeter you can have for the cost of the postage though.

Nick

On or around 16 Apr 2004 18:51:42 GMT, snipped-for-privacy@aol.com (Nicknelsonleeds) enlightened us thusly:

well, yeah, except you can infer that from the voltmeter too. Only thing I don't like about the LR one in the 110 is that it's not calibrated in volts. However, checking it against the multimeter produces the result that the mark in the middle is about 13.5V.

It might not be too hard to build a charge _indicator_, though the electronics might need a bit of care in the design. What you would need is to sense the voltage across the battery-to-chassis cable, which should be very low, but the polarity will indicate whether the battery is charging or discharging. Remember, the alternator has an earth path through the engine, and any current supplied by the alternator to the vehicle electrics will not be going through battery-to-chassis.