2nd alternator, 12V

rustystud

Well-known member
8,742
1,092
113
Location
Woodinville, Washington
You're fine, I'm not out to get you. Just happened to notice recent activity regarding a 12v topic.

At the same time, it is important to set the record straight that it has been done this way, per military design intent, on approximately 32,000 vehicles. The batteries in my M939 series were 7 years old when I received it, and all still in great working condition with plenty of reserve capacity left.
Does the M939 have a "Vanner" battery charger built in ? Our busses run four 12 volt batteries. There are taps off two of the batteries for 12 volt systems and then they all are connected (series/parallel) for the 24 volt system. The Vanner is connected to each battery charging them accordingly . If the military did this then there would be no problems with the batteries. Also if the 12 volt load is very light it would not be an issue.
 

74M35A2

Well-known member
4,147
275
83
Location
Livonia, MI
No equalizer. They run one or two items from the 12v tap. One for sure is the low speed for the heater blower. No power resistors to do so. 24v on high, 12v on low, same motor, single windings. I think it is about 6 amps on high and therefore 3 amps on low. Forgot what the second item was if it exists, but I think it is less of a draw than the blower motor.
 

rustystud

Well-known member
8,742
1,092
113
Location
Woodinville, Washington
No equalizer. They run one or two items from the 12v tap. One for sure is the low speed for the heater blower. No power resistors to do so. 24v on high, 12v on low, same motor, single windings. I think it is about 6 amps on high and therefore 3 amps on low. Forgot what the second item was if it exists, but I think it is less of a draw than the blower motor.
On a load that small I could see the military just going straight to the single 12 volt battery.
 

Castle Bravo

Hundredaire Socialite
Steel Soldiers Supporter
1,934
102
63
Location
Arizona
I think the other 12v thing on the M939 is part of the ABS system and is hooked up the same way.

I just finished converting my M916 to a 24v alternator. The stock OEM arrangement is an 85 amp 12v alternator with a 15A 24v transformer rectifier hooked to the back of it. The starter and trailer 24v connections are the only 24v systems on the truck and the rest is 12v.

I replaced the 12v alternator with a 24v 130A alternator and added a 24v-12v battery equalizer. So far, so good, but I probably haven't had it long enough to make a complete assessment. I have 4 batteries, so I have quite a "buffer" even if the equalizer doesn't work. My M916 is now setup like the Freightliner M916A1/A2/A3 is, as far as the starting/charging system goes.
 

74M35A2

Well-known member
4,147
275
83
Location
Livonia, MI
I think the other 12v thing on the M939 is part of the ABS system and is hooked up the same way.

I just finished converting my M916 to a 24v alternator. The stock OEM arrangement is an 85 amp 12v alternator with a 15A 24v transformer rectifier hooked to the back of it. The starter and trailer 24v connections are the only 24v systems on the truck and the rest is 12v.

I replaced the 12v alternator with a 24v 130A alternator and added a 24v-12v battery equalizer. So far, so good, but I probably haven't had it long enough to make a complete assessment. I have 4 batteries, so I have quite a "buffer" even if the equalizer doesn't work. My M916 is now setup like the Freightliner M916A1/A2/A3 is, as far as the starting/charging system goes.
I also thought is was part of the ABS system, but wasn't sure enough to say so. Also, the ABS was added on after, so not part of the initial truck schematic. The ABS is fused at 3 amp and 15 amp, not sure which is which.

Castle, what 24v / 130a alternator did you use?
 

Castle Bravo

Hundredaire Socialite
Steel Soldiers Supporter
1,934
102
63
Location
Arizona
I also thought is was part of the ABS system, but wasn't sure enough to say so. Also, the ABS was added on after, so not part of the initial truck schematic. The ABS is fused at 3 amp and 15 amp, not sure which is which.

Castle, what 24v / 130a alternator did you use?
Its a Leece Neville / Prestolite 4827JB. It is what the HET and HEMTT use. Some photos of the finished product here - http://www.steelsoldiers.com/showthread.php?81412-Photos-of-My-M916&p=1800132&viewfull=1#post1800132

Also attached a crude diagram of how the whole system is set up.
 

Attachments

Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website like our supporting vendors. Their ads help keep Steel Soldiers going. Please consider disabling your ad blockers for the site. Thanks!

I've Disabled AdBlock
No Thanks