anyone know how to test amps or current with a multimeter?

i put a dual battery system in my truck and she has always had starting problems so I wanted to be able to charge my batteries quicker, also with a winch the batteries will completely die. i ordered a 100 amp alt to install but i was curious as to how big of an alt is in there now. and i would like to know how to measure for future reference.

-cutts-

 

You have to have one heck of a multimeter, since most meters are only rated for 10A of current.

No good way since altogether it is possible to pull over 600 amps out of your battery all out.

Unless someone replaced it for, you'll have either a 45, 60 or 65 amp alternator. My guess would be on the 60.

when having charging trouble with our trucks, the first thing you need to do is to install a voltmeter. When you are at 14V, you know it is charging. when it drops below 14, and between 12-14V you know you are still charging, but something is sucking a some juice. When you are below 11.5-12V, you know your battery is being discharged.

The other thing to do is upgrade the wires from the voltage regulator to the alternator. On all of the trucks our age (80-86) I've worked on, the splice between the alternator wire, the wire that feeds the cab, the fusable link, and the wire that goes to the regulator is seriously corroded. I lost all alternator power on my '84 when it finally corroded enough. As a good temp. fix, I un-taped everything, cut off the corrosion, and wirenuted everything together with a big wirenut. works great to get you home. The best way would be to run an 8 gauge or thicker wire over to a fuse rated enough for your alternator (goto a good car audio store and get a distribution fuse block) and connect everything into the distribution block.

 

hmmmm, that's some really good info, thanx bremen

would you suggest the distribution block even after my alt upgrade?

right now i pull it in the shop every night and put her on the charger and she is good to go the next day. if i remember correctly i am getting about 12.3 or so volts so something must be pulling juice

-cutts-

 

I would still suggest at least a fuse, at minimum a fusable link, especially if you are getting a one wire alternator.

If you are only getting about 12.3 volts, that probably means your alternator is shot. The one in my beater would only get about 13 at an idle, as long as everything was off. To stay a little above 12Volts, you couldn't run the highbeams with the wipers and the defroster. you had to pick 1 or 2 and rotate them. I swapped the battery and alternator from my F-250, and now it charges pretty good, except that the F-250 alternator was a reman and kinda sucks a bit.

 

i checked last night and i am getting 11.3V at idle. i haven't checked at 2500 yet but plan on it.

-cutts-

 

you should be getting at least 13.5V at idle with everything off. If it reads the same at 2500, your old alternator is shot, or those wires are corroded very badly....

 

In order to check that much amperage you will need a current clamp.

 

I could be wrong, but I am pretty sure that those current clamps only work with AC current. I don't think DC generates the proper induction field for that.

 

Northerntools.com

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Tie-Down Digital Ammeter for 12V Applications
Lets you take current measurements in live circuits under operating conditions. Indicates direction of current flow. Provides precision electrical readings up to 1200 Amps, 199.9 V and 2000 ohms. Fuse protection and low battery/polarity indicators. Operates on one 1.5V 'C' battery and one 9V battery, included. Ideal for all DC automotive applications. UL listed.Model number= TIF1000DC U.S.A.
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Stock EETA501B
Turn your DMM into a clamp-on meter. Measures AC and DC currents greater than 10 amps (the limit of most DMM's) without breaking the circuit. Ideal for measuring starter current draw (amps) and automotive current draw. Used with DMMs that have 2V and 200mVAC and DC ranges. Range: 0 to 20 amp on 200mVAC or DC, 0 to 400 amp on 2VAC or DC.

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those would be the ticket.. I didn't think they made those for DC.

 

well, i got the new alt in only after breaking the long pivit bolt off in the head, so i had to kind of modify the bracket so i could use a bolt and a nut to hold it in.

now I have another prob......i got to skool this morning and went to class and when i came out and got ready to leave, the batts were just as dead as ever! they had a good 15 minutes at apprx 2300 RPM to charge! what's the deal here? what are all the connections on the back of the alt for? i only have 2 wires back there....pos and ground, should i have another? also my batt isolator is rated for 90 amps....anyone know where I can get a 100 amp isolator?

-cutts-

 

You are right on that. I was trying to remember if they could do d.c. after I posted.

 

I think there should be a stator wire back there.

And, my Autozones and Pepboys each have 100 amp isolators for sale.

If not, there are plenty of places online to order 'em.

 

> what's the deal here

Most likely the connection to your voltage regular is bad. On Fords the wires pull out of the connector or the connector falls away from the voltage regulator since the wire harness is unsupported. What I do is run a small zip tie around the voltage regulator and connector. Then drill a hole in the fender liner or radiator support and add a clamp. Then I force the wire harness into the connector and then zip tie it down there. That way it stays forced up into the voltage regulator and there is no stress to vibrate it down or weaken the connectors/wire/crimps because it is clamped/tied into place.

You can buy replacement connectors for the voltage regulator at NAPA for $18.00.

If you know someone with a carbon pile tester for batteries (most alt. rebuilding places) they can test your current draw. Though these usually cost $500+ and are pretty hefty. Using one I found my BII drew 23-30 amps just at idle. So, a stock alt. 60 amp alt. on an EFI vehicle does not leave much room for add-ons or high powered lights.

 

Sears may also still offer their combination "Engine Analyzer". It has dwell tach volts and a resistor bridge that will allow you to measure alternator current.. I bought mine 4-5 years ago for about 30-40 bucks. Also, you may also find the formula of AMPS x VOLTS = WATTS helpful... for example: 1 HP electric motor requires about 750 watts, so at 12 volts you are looking at a whopping 62.5 amps of current. GL