Ammeter shunt

[DJMTruck]

I converted my '53 3100 to 12 volt last winter and haven't had any problems, however, I've read here about the need for an ammeter shunt. I replaced the generator with an alternator but I'm not sure the size. Do I need to install an ammeter shunt and, if so, where do I get it? Thanks

[Deve]

This is something I am working very hard on DJM. I have emails out to every Alternator manufacturer out there and I have been unable so far to get a decent answer. You need to find out what your Alternators output is. This is VERY important if you exceeded the magic number. The magic number for our Stock trucks is 50 amps. This is the number that our stock ammeter gauges are rated for. If you exceed the 50 amps, you run the risk of overheating your wiring and burning out your gauge. I would love for some one else to chime in here about this because I want to know what we can do if we have a larger alternator. I thought of running a 50 amp fuse in the charging circuit, but the big question there is, "Under what circumstance would an old truck ever see more than 50 amps in charging current during normal operation?" Nobody so far has been able to answer that. To answer your question, there are no shunts that are matched to our stock gauges for a specific larger size alternator. I have researched Shunts pretty heavily and came up empty. It's a GREAT question and one I will not give up on until we have a better understanding.

http://devestechnet.com/Home/Native12VUpgrade#gauges

[DJMTruck]

Thanks, Deve. I have installed a 50 amp fuse in the charging system, just in case. So far, so good. I appreciate your reply & will stay tuned.

[DJMTruck]

I found some literature that came with my alternator, FYI. It is a NAPA 213-4011B and the info contains an output current (oc) table which notes increasing oc with increasing rpms. At 2000 rpm, oc = 52 amps; 2400 = 65; 3500 = 82; 5000 = 89; 6000 rpm, oc = 92 amps. Given this info, it appears that my oc exceeds the "magic" 50 amps for this truck. As noted, I've installed a 50 amp fuse between the ballast resistor and the ammeter and no problems yet but I'd sure add a shunt if I could figure out what to put in there.

[Deve]

It was a good idea putting the fuse in. Your truck, (providing its a 216/235/261) the max RPM it's capable of is about 3500. So, have you ran the truck out on the road at high RPM? That would eliminate the thought that maybe higher RPM alone would cause an over charge situation and blow the fuse. The battery only accepts current at a certain rate. The problem is, I am still trying to ascertain what that rate is! Thanks for sharing all this. WE WILL get to the bottom of this. I am still hoping for some return emails.

[DJMTruck]

Right, the engine is a 1960 261 installed by the previous owner. I've had it out on the road at 65 mph and no problems. I'll stay tuned in to this issue and greatly appreciate your info! I have another question about the 261's oil filter but will post it more appropriately.

[Deve]

I updated the information about this issue:

http://devestechnet.com/Home/Native12VUpgrade#gauges

I think we pretty much have this issue as resolved as we are going to get it. Check out the info and tell me what you think.