Just Purchased my first MEP803A!

[Guyfang]

Its hard for me to see what the problem is. Why don't you get the -24 TM out, and test the the meter IAW the TM? In the time its taken you to write the last 3-4 messages, you could have your answer already.

 

[Mweiss]

I did a few tests today:

Placed a voltmeter across the battery meter terminals and started the generator. It read -5mV then ramped down to -3mV.

Then I did the removal of FU1. With it removed, the needle moved less than 1mm into the red, about a needle thickness. With the fuse installed, it moved maybe 2mm into the green. Certainly a lot less movement than I've seen on other videos.

I assume that if the alternator weren't charging, the generator would shut down when the battery is disconnected for lack of energy to the fuel solenoid, am I correct?

 

[rickf]

Have you put a voltmeter across the battery terminals while it is running? That is a very simple way to find out if it is charging. You are WAY overthinking this!!!!!

 

[Mweiss]

A few days earlier I did put a meter across the alternator terminals as instructed, and read 26.5 volts with engine running.
I just want to be sure the unit is 100% working the way intended.

Does anyone know how many millivolts it takes to deflect the meter full scale?

 

[Light in the Dark]

Well when you took the fuse out, the gauge did read into discharge territory... And when put back in, it did move into the green (and then settled back to a neutral state). With the voltage reading, I think its all working right. Remember you got two brand new batteries in that machine.

Best thing you can do is hit the TM Guy mentioned and test accordingly.

 

[2Pbfeet]

Or just a clamp amp meter on the alternator output...

 

[Light in the Dark]

Or just a clamp amp meter on the alternator output...

Or a standard handheld MM picking up a ground and the positive terminal.

 

[Light in the Dark]

Mark pull down TM 9-6115-642-24 (or reference it if you already have it).

2-43 BATTERY CHARGE AMMETER. (PDF Page 116)

 

[Mweiss]

Thanks for the pertinent page of the manual. As I mentioned, I did that test and it peaked at 5mV and rolled back to about 2 mV after a few moments.

Those must be some super-duper low internal resistance batteries, because I watched one other video last week where the presenter mentioned he just installed new batteries, and the meter on his swung well into the green after startup and then settled to the border between red/green. Mine pretty much sits there like batteries have no sag when the starter engages.

 

[rickf]

Keep in mind that you are using two modern batteries to start a rather small generator. The biggest draw is the initial 1 second of spinning up the generator rotor. After that there is very little draw. Coming out of two brand new automotive size batteries. I would bet that the total draw to start that set pulls less than 1% of the capacity of those batteries. Because of that you never really have to put a full charge into the batteries. Keep in mind with all these videos you are watching that you have no idea the condition or age of those batteries. Plus, this is a volt meter, not and amp meter so it is reading the condition of the batteries. Not the charge rate. I would never say a gauge on a piece of military equipment is bad but the facts prove otherwise. I have had dozens of gauges go bad, or give false readings on this stuff. Sometimes it is not the gauge, it is a loose or dirty connection somewhere in the system. Anything from a loose battery cable to any of the hundreds of terminals inside the set. The only way you will know for sure is to open the wiring diagrams and start following all of the circuits related to charging and that gauge. A wire that is partially chewed through by critters will severely impact charging, and anything else that draws current. The voltages you gave for the batteries was not the 28 volts I would expect to see but it did show charging. I am not familiar specifically with the 803 gensets but the systems are the same across the board as far as charging theory. If you run it for an hour do the batteries come up to 28 volts? If yes then the charging system is working. If not then start looking for wiring issues. If this unit has a separate alternator as I think it does then check the output at the alternator. Maybe even take the alternator to a store to have it tested. I am the LAST person to ever say RTFM, I like to help people out but there are times when we may not be available. So you need to become familiar with what you are working with. If it goes down in the middle of the night during an emergency you are most likely no going to get anyone on here to help that quick.

 

[Mweiss]

I was surprised especially since the batteries that are in there are much smaller than a standard car battery, only taking about 2/3 of the battery tray width. So I would have expected some sag on startup, but who knows?

As I mentioned, I saw a video recently where the presenter mentioned brand new batteries just installed, yet, I saw that meter swing over to the right after it started and then swing back to the borderline.

I had a choice between this one that was just reset with 2 hours on the clock and one for less money that had 400 hours on the clock and a fuel gauge that didn't work. I went with the more expensive one for two reasons: the local seller lacked the means to put it onto my truck and my excavator is down with a burst hydraulic hose up in the Rotex gear assembly, so I have way to lift it either. The more expensive unit has a trailer so I can move it around. The other reason I went that route is so that it would not be a "project". I'm fine with a repair project if I paid only $1200 for something, but I'm old now, with a heart condition and overwhelmed with other emergencies such as a leaking roof to deal with myself. So I bought with the intent that it would be 100% working. It may well be, I'm just not sure because of the gauge behavior I see in many videos--even with new batteries claimed by the Youtuber.

I think the alternator MUST be working, because the fuel solenoid remained engaged when I disconnected the battery as a test. More likely the gauge is either stiff or stuck movement in there, or something else. Just doing my due diligence.

And finally, one more question. I've been regularly checking the level on the coolant overflow bottle when cold. When I got it, the level was almost half. After 2 hours of use, I see the level is around 1/4, or a half quart lower than before. I don't smell any antifreeze and saw no evidence of a leak, so where did the fluid go?

 

[2Pbfeet]

The overflow bottle is there to purge air out of the system. When the coolant heats up, the pressure is vented into the bottle, which includes any gas, or air. On cooling the vacuum, sucks only coolant back in. After a few cycles, on most reasonably designed engines, the air and therefore the oxygen, is purged out of the system, and all engine parts have good thermal contact with coolant.

Keep the coolant bottle with at least enough coolant to keep an inch or so above the return when cold. I recommend using the universal filler funnels that another member here recommended as the funnels enable running the engine while keeping the top of the radiator flooded.

There are engines that the coolant has to be changed under and by vacuum because of gas traps designed into the cooling system, and some designs are so extreme that they can lead to early engine failures because the gas is not readily displaced by coolant flow. There are lots of tradeoffs in engine designs, but that's not one of my favorites. I worked on one engine that absolutely needed a gas vent port at the top of the head, and did not have one, but the fix was repeated vacuum purging, as the manufacturer stated a run time of minutes if the gas was not completely removed. Yes, a bit of a pain to service. YMMV...

All the best,

2Pbfeet

 

[Mweiss]

So it's different than automotive overflow bottles that just act as expansion tanks, filling when hot, emptying back into the radiator when cold?

You're scaring me about this vacuum requirement. I know that's the case with refrigeration, but never heard of an engine where you can't flush the system and refill it. What specific engines have this odd requirement? By 'gas' you mean air pockets in upper parts of the water jacket? Does this apply to Lister-Petter engines?

 

[2Pbfeet]

So it's different than automotive overflow bottles that just act as expansion tanks, filling when hot, emptying back into the radiator when cold?

You're scaring me about this vacuum requirement. I know that's the case with refrigeration, but never heard of an engine where you can't flush the system and refill it. What specific engines have this odd requirement? By 'gas' you mean air pockets in upper parts of the water jacket? Does this apply to Lister-Petter engines?

No, I didn't intend to scare you with this. Yes, it functions just like a coolant overflow bottle on most engines.

The only unusual thing to me about the MEP-803 radiator cap is access / location, and that tends to leave behind a little more air than radiators with the cap at the high point of the cooling system. Hence the recommendation for the coolant funnel, like this one;

https://www.amazon.com/gp/product/B09XT1XC55

The engines that I was referring to are more modern high performance engines, where the aerodynamics tend to push the radiator below the engine, and have coolant returns that don't exit from the top of the block. I own one in an otherwise great truck, that requires flowing clean water for flushing, then the disconnection of main hoses to drain, then several rounds of distilled water changes to flush any residual ions from the flowing water. It is nuts. Basically, it requires four or five engine coolant volumes of distilled/RO & deionized water to change coolant. Oh, and the manufacturer discontinued the original coolant chemistry and the replacement coolant chemistry "curdles" the original coolant into granules of sand if old coolant remains in the system. Lots of awards to hand out around that one.

The Lister-Petter engines are fine, indeed very robust in my opinion, though I think that the parts can be a challenge to run down sometimes, since they used so many different vendors over the years.

All the best,

2Pbfeet

 

[Mweiss]

Your post prompted me to do some research. Apparently we're supposed to use a special coolant fluid:

" To counteract the effects of cavitation, diesel coolant contains special additives (primarily nitrite). Nitrite works by coating the metal components that are in contact with the coolant. The nitrite coating cushions and absorbs the impact the cavitation bubbles. "

Should I top off the fluid, which is green in color, I would want to know what the correct and proper coolant to use is. Probably buried somewhere in the TMs.

Glad to hear it's not a requirement to vacuum the system, though I have watched a couple of videos on the procedure and in some ways, the ability to recapture old coolant may be less messy.

I used to have access to DI water when I was at National Semiconductor in 1974. But nowadays, I don't have a need for it, nor would know where to get it.

 

[Light in the Dark]

Just use Prestone Green, premix is easier. Thats what they use at the depot level.

 

[Light in the Dark]

...but never heard of an engine where you can't flush the system and refill it. What specific engines have this odd requirement? By 'gas' you mean air pockets in upper parts of the water jacket? Does this apply to Lister-Petter engines?

These engines and radiator can be flushed and drained. There is a petcock drain at the lower corner of the radiator, and one on the engine block near the fan belt. Just follow the black hoses from the coolant tank, and you will find both.

When I drain and refill one of these, I always do so with the roof off, and thermostat out. After its been flushed, I backfill the system through the water pump to level, then reassemble, and tip the machine and finish at the radiator neck. Its still not foolproof... but it helps.

 

[Mweiss]

Some waveform tests I did this evening. Interesting that it cleans up under a heavy load. EG4 chargers have a .99 power factor.


No Load (except oscilloscope and isolation transformer:


Contactor turned on, powering two exhaust fans:


Fans + two 5kW Chargeverters running:

 

[rickf]

Pro tip, Never take the battery cable off of the battery while the engine is running in anything equipped with an alternator!!!! The resultant spike can take out all kinds of electronics on the vehicle/machine. This was something they did back in the days of generators on cars and it worked fine there, They produced 13.5 volts of DC power and that was it. An alternator produces higher voltage and it is also AC voltage which is converted by the diodes in the alternator. Which are one of the first things to give up the magic smoke when you do that.

 

[rickf]

I was surprised especially since the batteries that are in there are much smaller than a standard car battery, only taking about 2/3 of the battery tray width. So I would have expected some sag on startup, but who knows?

As I mentioned, I saw a video recently where the presenter mentioned brand new batteries just installed, yet, I saw that meter swing over to the right after it started and then swing back to the borderline.

I had a choice between this one that was just reset with 2 hours on the clock and one for less money that had 400 hours on the clock and a fuel gauge that didn't work. I went with the more expensive one for two reasons: the local seller lacked the means to put it onto my truck and my excavator is down with a burst hydraulic hose up in the Rotex gear assembly, so I have way to lift it either. The more expensive unit has a trailer so I can move it around. The other reason I went that route is so that it would not be a "project". I'm fine with a repair project if I paid only $1200 for something, but I'm old now, with a heart condition and overwhelmed with other emergencies such as a leaking roof to deal with myself. So I bought with the intent that it would be 100% working. It may well be, I'm just not sure because of the gauge behavior I see in many videos--even with new batteries claimed by the Youtuber.

I think the alternator MUST be working, because the fuel solenoid remained engaged when I disconnected the battery as a test. More likely the gauge is either stiff or stuck movement in there, or something else. Just doing my due diligence.

And finally, one more question. I've been regularly checking the level on the coolant overflow bottle when cold. When I got it, the level was almost half. After 2 hours of use, I see the level is around 1/4, or a half quart lower than before. I don't smell any antifreeze and saw no evidence of a leak, so where did the fluid go?

I will bet the batteries he used are 51R's these are in fact batteries for most Honda cars for 20 plus years, They are an almost direct replacement for the military 2HN battery but with twice the amp rating.