As members have pointed out many times, voltage only tells half the story.
I would like to hook up an ammeter to my 850 GLT. It is a shunt type, but I am not sure where to tap into the charging system. Wiring in series with the battery will just cook the gauge when you go to crank the engine.
Is there some other place I could tap into?
Txs
Jim

 

I think you'll have to modify the wiring. I looked at the 850 wiring diagrams, and they're not organized the way I would like, but it looks like the battery branches to all the loads and the alternator separately, and of course the starter.

You want the batteryto have two cables to two destinations: The starter, and everything else. You want the ammeter in the line to everything else.

 

What is it you're trying to measure? If you just want to see if your charging system is working, a voltage gauge will tell you that, and would be easier to wire into your car.

 

Ammeters generally can't measure too high without frying up unless they use an inductive clamp. What you need is a voltmeter if you want to monitor your battery and charging system.

 

I think you guys are missing his point of wanting to measure amps. Voltage only tells the electrical pressure, so the volts could be high but if the amps are low then that could lead to issues of not having power

 

But measuring amps all the time won't tell much. It isn't like a 120 amp alternator is always putting out 120 amps. The amperage depends on the load but the voltage should be about the same.

And, as mentioned, a typical low cost ammeter might measure up to 10 amps before it blows a fuse.

 

joco; suggest you read this before you buy an ammeter:
Auto Meter




What do you think a ammeter will tell you that a voltmeter will not?


A fully charged battery has a no load voltage of around 12.6V. As long as the charging system is higher than that, the battery is being charged.


The other thing you can monitor with a volt meter (and can't with an installed ammeter) is battery condition. Watch the battery voltage when you're cranking the starter; if it drops below about 9v during cranking, your battery is low and/or near its demise.


Keep in mind neither installed meter will tell you if you have a parasitic draw; you still need to do some diags to find that.

 

Thanks for all the comments, but like I said in my original post, voltage is only half the story. I already have a voltmeter installed, but I want to know more about the charging and electrical system. If you don't have the correct current you will have problems. Nice to know how much those electric seat heaters really draw, etc.. You could have the correct voltage at the battery but be just trickle charging it.
Looks like putting one in is not straight forward though....

 

Voltage equals amperage times resistance or "v=ar" so if you know voltage then you can make a good assumption about amperage and resistance because they are all related. There is NOWHERE you can put that ammeter that will tell you MORE useful information even if the ammeter could handle it.

 

I still don't know what you plan to use the info for. When the alternator fails, the battery light will come on

 

Hey Kiss4afrog, isn't time you weighed in here and help explain...

 

Are you trying to measure the current from the alternator or the current consumption by the vehicle?

 

This might be what your looking for, although I can't be sure. It measures voltage too. I am interested in your pursuit since I have ran an inverter with too much of a load and killed my battery. I have an AGM battery now but haven't recreated the same load yet. Keep us posted.

 

Yes, that is exactly what I want to wire in. Some people don't understand that you could have good voltage but poor current when you need it. The dashlight would not help you in that case. Sometimes an alternator fails in such a way that the voltage is still good but it cannot supply the necessary current to keep the battery charged up in a timely manner. This is the condition that I want to monitor for.
J.

 

I see I'm the only person who answered your question, but I am ready to answer it a second time. I had a 2nd thought, since you didn't seem to like the first one.

You could wire in an ammeter behind the alternator and measure alternator output only. You'd never see the actual balance of amps, nor any draw, but you would know what the alternator is putting out.

I suppose you could wire in two ammeters, one to show production and one to show consumption. I would not do that; I would just modify the wiring instead. It's not a big deal.

 

Well, I'm thinking about installing cameras at the suspension points and under the hood to monitor shock/strut movement and hoses for leaks & swelling while under operation.

 

I understand the difference between amps and volts. But reading what the alternator is putting out is not very helpful, since the output varies based on load.

Having replaced hundreds of Volvo alternators, I cannot remember a time when one failed to charge and the warning light did not come on. You are worrying about something you don't need to worry about.

 

wrong. As I stated before voltage is equal to aperage multiplied by resistance (or "load") therefore, if there isn't enough amperage to keep up with the load, voltage WILL go down. It's middle school algebra.

besides, unless you can wire that ammeter to the chargeback wire of the alternator, you won't get any useful information about the charging system amperage. But you can't because the alternator puts out between 80 and 120 amps and will kill your ammeter.

 

Wow, this is turning into a pissing match; i was just going to sit back and enjoy the nonsense but here i go getting sucked in again..

Actually kyle, you're incorrect (if i understand what you're saying here). You seem to be saying current will drive the voltage in a circuit; that's actually a common misconception (don't worry, you're not the only one). It's the other way round; voltage is the driver.

You can't "make" current; the only way to make current is to apply a voltage to a circuit. You can have voltage w/o current in a circuit, but you cannot have current w/o an applied voltage.

OP: put all the ammeters in there you want; until you tell me what it is you're trying to measure, i can't help you. You did say this:

"Sometimes an alternator fails in such a way that the voltage is still good but it cannot supply the necessary current to keep the battery charged up in a timely manner. This is the condition that I want to monitor for. "

What is this mysterious failure mode; i would like to know...

 

wow. I never thought this was a big deal. In the old days it was quite common to see trio guages. Volts, amps and oil pressure. Something is not quite right with my charging system. After start, the voltage drops and then rises. After that I have good voltage, but i don't seem to get a fully charged battery unless I go for a longer ride. So I thought it would be good to know what kind of current is going back into the battery. In searching posts on this forum, several members have claimed you can have good voltage but poor current. That is the condition I wanted to test for. I liked "firebirdparts" replies, so I have a good idea on how to proceed now. Thanks for all the responses.