Conecting an Ammeter gauge

[Steve K-B 51]

Hey all, I know this isnt related to BMWs but I wasnt sure where to post it.

Ive just got a cheep Ammeter gauge from repco for my corolla but cant understand the broken english on the instructions. Ive had a look on the net but cant find much to help me. Soooooo.......

Where do I connect the wires?

From what I understand one goes to the positive on the battery and the other goes to the alternator charging wire. I dont understand how this is sup post to work as the two wires connect together at the kill switch. Im a bit lost so any help would be awesome.

Cheers

[bravo 34]

An ammeter measures current through a circuit - normally would be connected in series to the circuit??? School-C physics here.

Just checked on our boat wiring - ammeter is in series between alternator and battery positive.

Edited March 10, 2007 by bravo

[Steve K-B 51]

Thanks Bravo, your right about being in serries. I didnt think about it really but the alternator could well push out more than 60amps as the gauge only goes to 60 each way. Maybe I should have got a bigger one......

If I do run it in serries with the alternator, will still measure negative amps from the battery? Ie not charging?

[will 169]

Thanks Bravo, your right about being in serries. I didnt think about it really but the alternator could well push out more than 60amps as the gauge only goes to 60 each way. Maybe I should have got a bigger one......

If I do run it in serries with the alternator, will still measure negative amps from the battery? Ie not charging?

I doubt if it would push more than 60 amps unless you current demands exceed 60 amps. If your battery is completely down it will go way over, and if you disconnect the battery while running it will do the same, go way over. The battery normally provides most of the current requirements and the alternator is really just there to keep the battery topped up. If you put it between the alternator and the battery it will show charge rate at any given time, between the battery and the car supply it will show current demand linked with supply, so may show + or - amps depending on demand at the time.

Will

[Steve K-B 51]

I doubt if it would push more than 60 amps unless you current demands exceed 60 amps. If your battery is completely down it will go way over, and if you disconnect the battery while running it will do the same, go way over. The battery normally provides most of the current requirements and the alternator is really just there to keep the battery topped up. If you put it between the alternator and the battery it will show charge rate at any given time, between the battery and the car supply it will show current demand linked with supply, so may show + or - amps depending on demand at the time.

Will

Cheers Will,

The car dosnt get used alot so the battery has been dead flat before as im sure it will happen again so thats why im worried about the gauge not being able to handel it. I under stand about it showing charge rate if its placed between the alternator and battery, But will it show in the negative? Im thinking the current draw for my accesories will by pass the gauge as I have all of my acceseries running of the starter cable from inside the engine bay or the switched side of the kill switch in the cabin. (the alternator wire joins the battery side of the kill switch and there are NO acceseries fun from that circut.

I think this is my problem.......

[will 169]

If you want a true reading you will have to put the gauge between the supply and the equipment. However, putting it between the alternator and the battery will give you an idea of what charge rate is needed to keep the equipment going. If you know the capacity of your alternator you will know whether you are drawing max from the alternator at any one point in time.

[Steve K-B 51]

Thanks for the input guys,

If I was to get a new 100 or 120 amp ammeter and wire it in serries in the starter cable before the kill switch, that would give me the total possitive and negative current draw from the battery wouldnt it?

I bought the gauge to keep an eye on the charging system as it has faild twice already, I have a volt meter in the car allready so that would be used to tell if the car wasnt charging at all. Should I just hook up the ammeter to the altinator possitive wire to keep an eye on charge amps? This would only tell me the performance of the altinator and may give a warning if it was on its way out I guess. Its alot easier to do it this way anyway, altho I would need a larger rated ammeter.....

Do you guys see any problems with this set up??

Cheers

[cainchapman 0]

What has failed in your charging system? Measuring the current draw on a working auto system would be reasonably meaningless. At no load if it is drawing current, that is helpful. An alternator that produces voltage you would also reasonably assume was delivering current.

Getting a bigger scale ammeter is beyond me too. What are you trying to prove? If your battery is flat. Take it out if the car, get a DECENT charger and leave it on for 48 hours on Float charge. Then fit it to your car. This will remove the massive loads on the alternator.

The 2 most useful things I have learnt in Electrotechnology.

Current always flows in a loop.

Voltage never exists on its own

Edited March 11, 2007 by Cain

[Steve K-B 51]

Ive never run the car hard in any thing longer than a hill climb and ive got a few rallys coming up so im trying to keep a better eye on things. Id really dislike to be put out of an event from mechanical failer.

What has failed in your charging system? Measuring the current draw on a working auto system would be reasonably meaningless. At no load if it is drawing current, that is helpful. An alternator that produces voltage you would also reasonably assume was delivering current.

Getting a bigger scale ammeter is beyond me too. What are you trying to prove? If your battery is flat. Take it out if the car, get a DECENT charger and leave it on for 48 hours on Float charge. Then fit it to your car. This will remove the massive loads on the alternator.

The 2 most useful things I have learnt in Electrotechnology.

Current always flows in a loop.

Voltage never exists on its own

Ive had the alternator possitive wire break of and screw my regulator as well as an altinator failing all together. Im not worried if the electrical system is working fine (as it should and does at the moment) its when somthing stops working that I want to know about it so I could do somthing about it before a total charging loss, and I was hoping an ammeter would be a good indercator.

Im hoping to keep an eye on the current draw to and from the battery as this would indcate a problem with the ACC draw or charging output and as the way the car is wired, I would have to put the gauge inline with the starter cable for this to work, this is why I would need a larger ammeter but as 3pedals has pointed out this is pretty much not an option. I do charge the battery before I use it and as often as I can remember to when its not being used. Altho It has gone flat over time when I do forget!

I like "Voltage never exists on its own" and as you said an alternator producing voltage would be producing current, maybe I dont need an ammeter at all?? Just keep a better eye on the voltmeter?

Don't include the starter motor in the circuit as it is a temporary use item and it suck huge currents 200 amps plus and if you stall it (like have it in gear and try to start it) you can be looking at 600 amps plus.

A charge / discharge ammeter will tell you all you need to know.

Basically the only time you should be looking at a discharge is when you are running lights / sounds etc with the engine off

All light, wipers and sounds in traffic should get close to "0" any other time should be charging - heaviest charge will be immediately after starting

Also if you have a noticeable current discharge when the key is completely off, then you have a fault that needs finding.

There are several problems that can contribute to low charge, put the ammeter in and tell us what you get and we will help you solve it if you still have a problem.

Good point with the starter motor, I didnt think about the extra amps if cranked in gear etc. A charge/discharge gauge is what I have but as I said above I cant measure what I want anyway I look at the wiering on my car. I do plan on running night time lights that will draw large a current but how many I have no idea. Ive done one night hill climb and ill never do another one just running the standard lights! Scary......

So now the question: Looking at what Cain and the rest have said, do I really need an ammeter if I have a voltmeter??

[cainchapman 0]

3pedals is correct on the voltage measurement from the alternator. If it is isolated from the circuit, then it would be possible (and probable) that voltage would be present, and a collapsed winding would not be diagnosed.

If you are running it as a hill climb car, I'd suggest running it as a total loss setup. Ditch the extra electrical gear. Fit a good battery (a suitably sized Odyssey) and an external battery to start the car with.

Make sure both are fully charged and you will be sweet. Most of our races cars runs this way. You just need to have the discipline to charge them up each time you use them and for 2 days prior to the next usage after a break from racing.

If you are going to try to calculate the loading. Use the constant power ratings on the battery discharge tables (if you can figure them out) as the current tables will leave you seriously short for this application.

[conrod 1]

Don't fit an ammeter to your car, especially not a cheap one! The very nature of an ammeter introduces potential for problems, and I have seen many of them fail, the results anywhere from no charging to very burnt wiring. Trust me on this!.............

[hotwire 352]

Don't fit an ammeter to your car, especially not a cheap one! The very nature of an ammeter introduces potential for problems, and I have seen many of them fail, the results anywhere from no charging to very burnt wiring. Trust me on this!.............

DITTO!! Dont fit, really is superfluous for this application & as said they do fail & cause greef - especially cheap ones. The potential current through them can cause heat build up then meltdown.

A volt meter tells the story as to alternator charging state without the risk.

Admittedly doesn't show current charge / discharge but with a vehicle with a known total current demand & known alternator ouput that exceeds that potential demand then barring alternator /charging system failure (which will be indicated with low reading on voltmeter) then the system takes care of itself. Also a 60 amp range meter will not show a slight current leakage - eg shorted diode in alt. Ammeters aint worth the hassle.

The ony time I use one is when checking a charging system/ current draw on a car in the workshop.

[hotwire 352]

Cains' comments for a race car set up for short duration events are sound, you can make a standby start and charge system which is external to the vehicle.

You need to ensure the battery is fully charged to get maximum spark energy because it is related to the voltage squared.

If you take into account that a closed system operates at about 14 volts you have 196 ( 14 squared) the drop from 14 volts to 12 volts gives a 27% reduction to 73 % in coil output. If you end you event on 11 volts then you would start with 73% and finish at 62% or 27% to 38% reduction in coil energy.

So if you use the same ignition set up from a charging based system and go to a total loss system you WILL need to change the coil ballast resistor.

On the other " don't do it" comments """You get what you pay for!!!!!!!!!!!!""".

If you do choose to use an ammeter then use one with an external shunt that fits in to the existing electric circuit and has terminals that are up to the task. Then wire to the ammeter from the shunt so that no large currents are going through the gauge. This will prevent all of the issues listed by Conrod & Hotwire.

As per previous comments get a range that matches the probable draw and it will be useful.

If you go the Cain route ensure you have a good voltmeter and a fresh battery

If you stick with a standard closed automotive set up with alternator single battery then look into a good ammeter (with external shunt) to supplement the voltmeter and as above and think it through. A voltmeter will be of some use but as per earlier you get very little warning of a flat battery or extra current draw due to something like sticking brake light switch or similar

No automotive ammeter or voltmeter will tell you if you have faulty diode in your alternator.

Key to this is have the full system tested once you have completed it and know that at that time it is 100% okay, then you can have some confidence in its' reliability.

3pedals

Agreed with your comments - a shunt ammeter takes away the risk factor associated - I nearly suggested as an alternative myself but really I still question the "need" for an ammeter anyway.

With a known maximum potential current load in the vehicle v its alternator output a voltmeter will suffice for monitoring the system.

As for an automotive ammeter telling of faulty diode - was not suggesting they would but was merely pointing out that a 60 amp or even 30 for that matter wont show a fault like that - a fault with potential to cause a flat battery. Yes you may see a sticking brake light switch but in reality - how likely is that fault?

For diode leak or any other leakage I use a digital meter on 10 amp scale for precise measurement

With the above stats (draw v output) known the system takes care of itself.

A boken battery supply to the alt will show with a drop in voltage in the meter & regulator / rectifier damage will occur anyway if it was likely to with this senario regardless of an ammeter in the system.

Finally - yes you get what you pay for.