M20J Crazy Amps

[DC_Brasil]

Let's get the collective wisdom rolling

My M20J is fresh out of the avionics shop after installing a G3X panel.

Last week when I flew it, the R wing fuel gauge stopped working. Well the fuel senders are old and I am contemplating a switch anyways. The very next flight, when I tried to start the engine I turned the key the plane seemed like the battery was low. I thought it was odd but maybe I spent a little too long updating the navdata with the engine off. I started it with an external source and went flying. Everything seemed normal so I took it on a 2hr XC flight.

Today, flying back home I experienced the same behavior and had to use and external source to start up. Now, both COMM radios had an interference of a quick rhythmic "popping" sound.

Additionally, in cruise I could see the ammeter was showing some crazy readouts, going from -30 to -290 amps!!!

After I landed the ammeter showed a reasonable +2 amps. I tried turning on and off various systems and lights to see what I could find but no clue. Nothing particular happened. 

I suspect something is shorting the system and draining the battery. Perhaps the fuel sender line (it may have nothing to do with the electrical problem but what the hell)? Any thoughts?

Here are some pictures.

[exM20K]

I had something similar shortly after I got the Acclaim.  It was a battery with cells shorted out.

-dan

[Yetti]

Most likely you have a ground not attached firmly.   Start with the battery and then check the grounding strap that should be on the passenger side from engine to the firewall.      What your comms/EMS is grounded to is the most suspect.

Edited December 8, 2024 by Yetti

[EricJ]

One thing to try when you have a periodic noise in the radio static is to try a mag check, isolate L and R and see if it goes away when one of them is selected.   If so, it is ignition noise related to that mag.

 

[Yetti]

1 hour ago, EricJ said:

One thing to try when you have a periodic noise in the radio static is to try a mag check, isolate L and R and see if it goes away when one of them is selected.   If so, it is ignition noise related to that mag.

 

This is true.     What I would suggest here is because the ground is not good for the radio, the radio is seeking ground through the p leads inducing the noise in the radio.       Fun Fact you can run a RPM gauge using the P leads.   Dynon use the P leads to pick up RPM.

[DC_Brasil]

14 hours ago, EricJ said:

One thing to try when you have a periodic noise in the radio static is to try a mag check, isolate L and R and see if it goes away when one of them is selected.   If so, it is ignition noise related to that mag.

 

Hi Eric. I did a mag check before takeoff and in flight and it worked fine. Engine ran smoothly and EGTs responded properly to the single mag.

[DC_Brasil]

15 hours ago, Yetti said:

Most likely you have a ground not attached firmly.   Start with the battery and then check the grounding strap that should be on the passenger side from engine to the firewall.      What your comms/EMS is grounded to is the most suspect.

Would that explain the crazy ammeter readings? Sorry but I am very inexperienced with electrical circuits.

[DC_Brasil]

15 hours ago, exM20K said:

I had something similar shortly after I got the Acclaim.  It was a battery with cells shorted out.

-dan

My first guess was a bad battery. Will check that for sure!

[EricJ]

5 hours ago, DC_Brasil said:

Hi Eric. I did a mag check before takeoff and in flight and it worked fine. Engine ran smoothly and EGTs responded properly to the single mag.

Did the radio static go away with either mag?

[DC_Brasil]

8 hours ago, EricJ said:

Did the radio static go away with either mag?

I actually don't recall... will have to check that. 

[DC_Brasil]

Hello everyone.

I had a technician test the battery and it was in very bad shape. So I guess I found the source of the problems.

My battery was a Gill G-243. 

Can anyone help me find a list of suitable replacements? The tech advised me to get a sealed battery. However, I really don't have any knowledge about the battery and electrical systems.

[KSMooniac]

Concorde RG-35AXC

Edit to add that I retired my previous 2 of these after 7 years in service, each.

Sent from my motorola edge plus 2023 using Tapatalk

[Hank]

29 minutes ago, KSMooniac said:

Concorde RG-35AXC

^^^ THIS ^^^

I'm two years into my 3rd one since 2008.

[Fly Boomer]

2 hours ago, DC_Brasil said:

Can anyone help me find a list of suitable replacements?

As noted above, Concorde RG-35AXC.  Friends don't let friends buy Gill batteries.

That battery will not magically fix problems with your alternator, regulator, starter, or cables, but if everything else is working correctly, it will last quite a long time.

[PeteMc]

Since the plane just came out of the Avionics Shop, don't discount that you may also have a loose ground(s) in addition to the bad battery.

 

[DC_Brasil]

8 minutes ago, PeteMc said:

Since the plane just came out of the Avionics Shop, don't discount that you may also have a loose ground(s) in addition to the bad battery.

 

I'll make sure to review all of that.

 

19 minutes ago, Fly Boomer said:

As noted above, Concorde RG-35AXC.  Friends don't let friends buy Gill batteries.

That battery will not magically fix problems with your alternator, regulator, starter, or cables, but if everything else is working correctly, it will last quite a long time.

I just saw at the Concorde website that specific model is 12V. My plane is 24V. Now I am  looking at the Concorde website that the two 24V batteries (RG24-15 and RG24-11M) are not suitable for my plane's Serial #.

I have emailed Mooney and see what comes back.

[Bolter]

4 hours ago, KSMooniac said:

Concorde RG-35AXC

Edit to add that I retired my previous 2 of these after 7 years in service, each.

Sent from my motorola edge plus 2023 using Tapatalk




 

Later J's are 28 volt systems.  The Gill 243 is a 28 volt, so the right concorde is probably RG24-15

[KSMooniac]

Concorde's eligibility list does not seem to break anything down by serial number.  The RG24-15 is TSO, although they have an asterisk indicating potential fitment issues.  The RG35-AXC had the same warning, but dropped right in to my 14V battery box just fine.  I suspect it is the same for your newer J.

Aircraft Eligibility list

[A64Pilot]

I would be real concerned with a discharge rate of 290 amps, even at 20V (hit a battery hard and voltage drops), that’s still 5,800 Watts, which is an awful lot as in enough to cause a fire.

A bad battery should not have anything to do with a discharge, once running the alternator is providing current, not the battery, so in my opinion it’s most probable that you still have a problem, and I doubt the -290 amps is real or you would have smelled burning wires.

A loose ground can cause all kinds of illogical problems, lots of things that just don’t make sense.

[PT20J]

I have a 28V M20J and use a Concorde RG24-15 which is on the approved list on the Concorde website and the Mooney IPC. It doesn't have the manifold, but you don't need it with a sealed battery. I asked Concorde why they made some models with a manifold and they told me its because the airframe manufacturer requested it. But, they said it is entirely unnecessary for normal operation with the battery in the tail. The M20J had several configurations of battery box. Mine was built for a sealed battery and so it just has a shelf and no box. If yours has a box, you'll need to check the dimensions carefully to make sure it will fit. I'd compare measurements and hold down location from your current battery to the RG24-15. The IPC has a note: REFER TO MAC DWG 940147 FOR RETROFIT DATA ON R & R FROM GILL TO CONCORDE 24V BATTERIES.  You might contact Frank Crawford (technicalsupport@mooney.com) for info on that.

[DC_Brasil]

1 hour ago, PT20J said:

 You might contact Frank Crawford (technicalsupport@mooney.com) for info on that.

I did that yesterday. Specially because the Concorde website listed certain serial numbers as appropriate for the RG24-15 and/or RG24-11. FWIW, I have email Frank at Mooney some times and he has always been very fast and helpful in his responses.

He sent me the information regarding that "Concorde battery retrofit". It refers to the suitability for all 24-3000+ serial numbered M20Js to use the RG24-11/15 batteries plus the need for a 1.5lbs adjustment in weight and balance if using the -15 battery, which is heavier.

I ended up ordering a RG24-11M, which was more readily available and had faster shipping. 

It should arrive next week and I'll get a tech to help me check all grounding and make sure everything will work.

The battery technician really thinks there is a high likelihood my grounding should be ok. From what he could see in the battery tests they ran, there was an internal short and it would explain the huge negative current.  If the short in the battery is intermittent, the ammeter could show large swings as the current draw spikes when the short is present, just like I experienced in flight. For example, I saw currents fluctuating from +2 to -290 amps. Also, the battery overheated when they ran a charging test. If one or more battery cells are shorted, they will convert charging current to heat (that's what I was told).

However, next week, when the new battery arrives, I'll run some tests.

Thanks for the inputs to everyone. This forum is a life (and pocket) saver.

[Yetti]

On 12/9/2024 at 5:16 AM, DC_Brasil said:

Would that explain the crazy ammeter readings? Sorry but I am very inexperienced with electrical circuits.

Yes.  Most of your oil temp, fuel tank sensors are resistance type gauges.   If you take the wire off the sensor and direct to ground, it will peg the gauge.    EGT/CHT thermocouple type sensors don't work in the same way.

 

[mooneyflyfast]

On 12/9/2024 at 5:16 AM, DC_Brasil said:

Would that explain the crazy ammeter readings? Sorry but I am very inexperienced with electrical circuits.

A loose connection. I had this on my J