m998 overcharging after startup

[crazzyrman]

My '86 m998 spears to be overcharging for 5-10 minutes after startup & then it settles out in the green range. It alternates between being pegged all the way to the right on the gauge & the green zone about every 30 seconds, I have the military LED headlights & when it is off the gauge to the right the headlight goes out & then it comes back when it drops back to the green.

 

[Bulldogger]

Could be several things, but hopefully not the engine controller

Have you checked the generator at the output, to verify the voltage swings manually (apart from the mil gauge)? You might also check your voltage regulator. The TM explains how. Not sure which generator you have, or if you have an alternator. On the 60Amp version that I have, the brushes in the generator made a lot of carbon dust, which can foul internal components, despite most being sealed in epoxy.

The LED headlights going off sounds like them shutting down due to over voltage, which would likely be a protective measure built into their power supplies. However, this kind of over voltage is not a good thing, so I recommend starting with all lighting OFF until this is cleared up. I start with mine off anyway because I get tired of the bright/dim cycle displayed while the after glow does its thing.

Bulldogger

Hopefully it's not your control box.

 

[crazzyrman]

Could be several things, but hopefully not the engine controller

Have you checked the generator at the output, to verify the voltage swings manually (apart from the mil gauge)? You might also check your voltage regulator. The TM explains how. Not sure which generator you have, or if you have an alternator. On the 60Amp version that I have, the brushes in the generator made a lot of carbon dust, which can foul internal components, despite most being sealed in epoxy.

The LED headlights going off sounds like them shutting down due to over voltage, which would likely be a protective measure built into their power supplies. However, this kind of over voltage is not a good thing, so I recommend starting with all lighting OFF until this is cleared up. I start with mine off anyway because I get tired of the bright/dim cycle displayed while the after glow does its thing.

Bulldogger

Hopefully it's not your control box.

Is this the same control box that controls the glow plugs? I'm also having cold starting issues, see my other post on this page.

 

[Bulldogger]

Is this the same control box that controls the glow plugs? I'm also having cold starting issues, see my other post on this page.

My bad, I didn't notice the companion thread. Yes, same box influences both. Sounds like the box to me. I defer to those who know more about the control box, in your other thread.

Bulldogger

 

[crazzyrman]

I was using the truck this weekend & it didn't give me any charging issue at startup this time, but while I was driving for a couple hours I would just randomly act up for a couple minutes & then go back to normal. I was running my wipers part of the time & they eventually failed while the truck was running in the green zone on the voltmeter.
at this time it appears I need a blower motor (it failed over the winter), a wiper motor (it got really hot when it stopped working so I'm assuming it's shorted), it sounds like I need the smart box (since it doesn't start worth anything anymore & I'm told it is or also controls the voltage regulator).
is there anything else I should be replacing with this "over voltage" issue I'm having, I don't want to put in new parts & just fry them again because I didn't resolve the actual problem?

 

[papakb]

There's a 50 ohm, 50 watt power resistor in the regulator casting that occasionally blows out that can cause this problem too. Luckily it's an easily replaceable part, just 2 screws. The other causes of voltage fluctuations are a bad regulator and worn brushes. All of this stuff is available from Southern Automotive here:

http://www.southernautomotive.com/catalog/advanced_search_result.php?keywords=ama5104&x=0&y=0

 

[Rmtaunton]

Mine did the same it was the internal regulator in the alternator it also fried my smart box


Sent from my iPhone using Tapatalk

 

[Bulldogger]

The TM shows how to adjust the regulator. Might need a tweak. Assuming you have the 60amp smaller one, which is a very common design on green machines by the way, it can be quickly adjusted or the regulator replaced. Mine tired out from age and dust from the brushes, a new regulator end plate fixed it right up. These 60A units are generators, not alternators, and the carbon brushes put a lot of dust inside them during use.

Your wiper motor could have fried due to the overvoltage of a badly regulated output, regardless of your type of power source (generator/alternator). I spotted and fixed mine before it had a chance to fry the smart box, thankfully. Anyway, a new regulator isn't expensive, for the 60A units, and can be found surplus on eBay or many other sources, since it is a common part to many vehicles. If you have a 100A or 200A version, parts can still be found, but I have no experience with those to share, apologies.

It is also a VERY good idea to check all connections. A bad battery connection to the posts of the vehicle (places where the power cables pass power through by being bolted to posts) is one that is often loosened or dirtied. If you haven't already, check all connections in your charging circuit inside and out. Remember if there's a post on one side, like the "outlet" of the batter compartment, there is a post on the other side, and a bit harder to see/reach. Those can get loose and since they aren't in plain sight can be overlooked...

You'll suss it out. They are not complicated vehicles despite their appearance.

Bulldogger

 

[papakb]

The 60 amp units made by either Prestolite or Leece-Neville are alternators, not generators. The way they work is the regulator assembly sends a voltage to the slip rings through the brushes to the rotor that controls the output voltage and current from the stator of the alternator. This is exactly opposite generators where the field is the stator winding and all of the output current comes through the brushes that ride on the commutator of the rotor. Either way, the brushes produce a lot of carbon dust that tends to short things out and needs to be cleaned away. The problem is worse in the alternators because the rear compartment where they live is sealed.

Adjusting the regulator is pretty easy. There is a hex plug beside the cover where the leads attach. By removing it you gain access to a potentiometer that can be adjusted with a #1 phillips head screwdriver. The adjustment is backwards from what you'd expect, turning it clockwise lowers the voltage and turning it counterclockwise increases the voltage. You can look at the meter on the gauge panel or put a meter on the output stud of the alternator. This is the large 8 gauge wire. The small line on the gauge in the green section is supposed to be a 28 volt reference but military gauges being what they are I wouldn't trust them and would recommend using a meter. Be extremely careful when you remove that little cover there's not much clearance between it and the power connections.

Most equipment in military vehicles is fairly voltage tolerant within reason. A volt either way won't kill things but setting the output voltage at 27. volts is recommended. Flooded lead acid batteries normally charge at around 13.6 volts per battery and sealed maintenance free batteries charge at a little higher voltage of 14 volts.