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MEP 803A testing alternator output

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chilbun28

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Hi everyone. Everything is pretty much good on my 803 at this point. Although the batteries I have in it are really old, the other day I went to crank it and they were dead. I charged them and ran it a couple times just fine and this morning it was dead again. I think its just the batteries. I think if I put them on a load test they would likely fail, but I'm going to try and do that tomorrow. Just trying to get ahead of myself, I figured I would check the system out and see what kind of readings I get from my alternator. I picked up 2 new group 51 batteries this evening on my way to work and plan to put them in tomorrow. Where exactly do I probe around with my multimeter to get the output readings? Also, I read where I could disconnect the battery cable between the two batteries while the unit is running to see if it dies or not. Just wanting to make sure I read that correctly before I do it and accidentally fry something. Electricity isn't really my strong suit. Thanks
 
flyfishtrailer

flyfishtrailer

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I am having issues with my computer and haven't been able to upload a photo, but if you look at the back of the alternator, there should be marked posts (POS and Neg). Just use your multimeter to touch the posts while its running for alternator output.
 
Guyfang

Guyfang

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Hi everyone. Everything is pretty much good on my 803 at this point. Although the batteries I have in it are really old, the other day I went to crank it and they were dead. I charged them and ran it a couple times just fine and this morning it was dead again. I think its just the batteries. I think if I put them on a load test they would likely fail, but I'm going to try and do that tomorrow. Just trying to get ahead of myself, I figured I would check the system out and see what kind of readings I get from my alternator. I picked up 2 new group 51 batteries this evening on my way to work and plan to put them in tomorrow. Where exactly do I probe around with my multimeter to get the output readings? Also, I read where I could disconnect the battery cable between the two batteries while the unit is running to see if it dies or not. ( You do not want to do that. Simply measure where the above posts tell you to, or at the Slave Receptacle. Outside is ground. Inside is Positive. Nothing simpler. If you want to see if the alternator is putting out, just measure at the Slave Receptacle before starting. Not it down. Then start the set. Measure again. If its the same, or lower, the alternator is not putting out.

And, removing the cable between the two batteries, is about as unsafe as you get. Drop the cable while the set is running, and you could have a light show you will never forget.) Just wanting to make sure I read that correctly before I do it and accidentally fry something. Electricity isn't really my strong suit. Thanks
 
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chilbun28

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With the old batteries I'm pretty sure the battery charge gauge would shoot up during start up and fall down to zero within several seconds. Now, with the new batteries it is showing its charging while it's running. Also, I have not checked the FU1 fuse, but I will when I get back home.
 
Light in the Dark

Light in the Dark

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chilbun28 said:
This is where it's running on the gauge now.
Click to expand...
If that's with new batteries, they are not fully charged. Battery quality has been piss poor since COVID... Much like the world. Let that machine run and see if the gauge ends up zeroing out (or put the batteries on a charger to make certain). Ive had bad batteries off the shelf new more than once in the last year.
 
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chilbun28

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Ok, another rookie question for you guys. Do I need to disconnect the battery cables and charge the batteries one by one or can I leave the batteries connected and charge each battery? I only have one 12v battery charger and not sure if I should disconnect the batteries or not.
 
jcollings

jcollings

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I have charged batteries separately with a 12 V charger I don't know if you're doing AGM or regular batteries, as they would require different chargers. I would also make sure the switch on the oil check side on the upper right is in the disengaged position (middle )so it's not normal and it's not the crank check, but disengaged if that's the right terminology

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