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Electricity load

gblwy

Well Known Member
Hi,

I’m struggling with electrickery. Over a space of 10 years I have added minor electrical stuff to the plane and, as a probable consequence, I’m having intermittent problems with the trim, possibly in turn due to low battery voltage. The battery is new so I’m wondering about the old chestnut of Ducati Voltage Regulator which was also replaced some time ago.

There’s nothing wrong with the trim motor. It works fine on the ground with a charged battery.

My estimate of the worst case steady state electrical load is around 14A, close to the alternator’s reported max of 15A. Adding the landing light takes the load to maybe 17A, but only runs for a matter of moments.

I have conducted a ground run incrementally adding to the load and noting voltage and current. With minimal load the voltage is around 13.5 during warming up with maybe plus 4-5A current.

At peak load at 4000 rpm the voltage is nearer 12.8 and current around 0-1A. The trim motor is sluggish and I guess may stop with air loads.

Do these figures make sense?

Thanks...Keith
 
Hi,

I’m struggling with electrickery. Over a space of 10 years I have added minor electrical stuff to the plane and, as a probable consequence, I’m having intermittent problems with the trim, possibly in turn due to low battery voltage. The battery is new so I’m wondering about the old chestnut of Ducati Voltage Regulator which was also replaced some time ago.

There’s nothing wrong with the trim motor. It works fine on the ground with a charged battery.

My estimate of the worst case steady state electrical load is around 14A, close to the alternator’s reported max of 15A. Adding the landing light takes the load to maybe 17A, but only runs for a matter of moments.

I have conducted a ground run incrementally adding to the load and noting voltage and current. With minimal load the voltage is around 13.5 during warming up with maybe plus 4-5A current.

At peak load at 4000 rpm the voltage is nearer 12.8 and current around 0-1A. The trim motor is sluggish and I guess may stop with air loads.

Do these figures make sense?

Thanks...Keith

It looks to me that your battery is not charging. 13.5 volts is too low to effectively charge you battery and at 12.8 volts, your battery is not charging at all.

Nevertheless, your trim motor should work fine at 12.8 volts. You need to find someone local with some experience with electricity. He or she should be able to figure this out quickly. Is James Clerk Maxwell available?
V
 
Keith-

Aside from what Vern has already mentioned, I'm wondering if you have the Dynon Autopilot Panel installed?

This may be a shot in the dark ... but if the Dynon AP panel is installed, there is a speed scheduler built into the Dynon software which is capable of decreasing the speed of the trim motor. If you have the AP pannel installed, you may want to have a look at the trim settings and make sure that at slower speeds that the motor is receiving 100% power. (I think I set mine to reduce the power to the trim motor for speeds over 90 knots and to apply 100% power to the trim motor for speeds under 90 knots).

Also, check the voltage that is actually making it to the motor ... you may be experiencing a voltage drop in one or more of the connectors on the way to the trim motor. For what it is worth, if you have the Micro Molex connector at the trim motor, that would be a good place to begin troubleshooting. The Micro Molex connector has been very problematic and is no longer supplied by Van's.
 
Also, check the voltage that is actually making it to the motor ... you may be experiencing a voltage drop in one or more of the connectors on the way to the trim motor. For what it is worth, if you have the Micro Molex connector at the trim motor, that would be a good place to begin troubleshooting. The Micro Molex connector has been very problematic and is no longer supplied by Van's.

Measuring the voltage at the trim motor is not a reliable way of confirming proper power feed to the trim motor.

The controlled trim speed output is from a PWM circuit. This is a pulsed DC output which can not be correctly measured with a DC volt meter. You will instead be measuring the RMS value of the pulsed DC signal. This is good enough to confirm that power to the motor is actually present, but don't be fooled into thinking that something is wrong when the measured value doesn't equal buss voltage.
 
Lubricate the AST hinge pins and linkage pivot points. If the trim is still too sluggish, adjust the trim speed pot.
Consider replacing the Ducati regulator with eBay item number 233489024206 or similar. Use heat conductive paste
between mating metal surfaces and install an air blast tube for cooling.
 
You might want to remove top plate on trim servo and check gears for lube.

I had intermittent trim problems with my early SN RV-12 a few years back and isolated the problem to the PWM circuit Scott mention in above post.

I ended up doing major surgery on the circuit board and removed the trim switch. I replaced with Ray Allen rocker switch and two-speed controller selectable with small toggle switch. Works a charm. Slow speed trim is ideal for cruise and fast speed trim is perfect when plane is slowed in the pattern.

The job is not for the faint of heart. Lots of cutting and no going back if you change your mind...
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Thanks, all. No autopilot controller fitted.

Trim components have been lubricated. I don't think the trim mechanics are the problem. I was required (in the UK) to set the trim speed at the slowest it would operate. That was 10 years ago and has only recently caused problems. The only change I am aware of is increasing electrical load.

I could try speeding speeding up the trim but I suspect it is only addressing the symptom, not the root cause.

I could just replace the voltage regulator but does the evidence point to a problem there, or is that suggestion just to eliminate one known problem area. Any checks I could perform beforehand to establish whether that is justified? Mine is still on the engine side of the firewall with ram air cooling.

I plan to conduct a decent flight (say an hour) with only the "standard" Vans-supplied electrical stuff switched on to see if the baseline configuration still works. The only additional stuff I have installed is USB-powered so individual components are not power hungry.
 
14A is quite a load. I don't know the 12 that well, what do you have running that requires that much power? You will of course have intermittent loads like fuel pump and flaps, but are your other electronics that hungry?

For anything electrical that recently changed, one area to look into is grounds - any chance something is coming loose?
 
Fuel pump is on 100% of time, flaps are manual.

0.5A Radio
0.2A Intercom
2.0A Transponder (but could go up to 4A)
1.5A Dynon
1.5A Nav lights
3.0A Landing lights (obviously only when needed)
1.5A Garmin GPS
1.5A Fuel pump
1.8A Electronic conspicuity devices
1.5A iPhone and iPad
2.0A GoPros (x2)

Last 3 items have all been added post-build, all USB-powered

I've powered on each item incrementally. No one item makes any significant difference (apart from the landing light).
 
If you replace the Voltage regulator, for future reference, in case the eBay # changes, do a Google search with this description.


AM101406 12V Voltage Regulator Fits John Deere 330 375 3375 332 322

IMHO, you really need to shed some electrical load, that much current draw will fry a Ducati regulator and the electronic components inside it. It was designed to run a Ducati 900 cc motorcycle from the 1990's that never had that kind of electrical load applied to it. A 45w 12 volt head light and a 5 watt 12 volt tail running light, with occasional Brake light of 10 watts and turn indicators of 10watts.

You've got too many electrical toys in your plane, IMHO. Shed some load or add another alternator and voltage regulator.

I am also pretty sure that when transmitting on your radio, you're pulling 2.5 to 3.0 amps, on transmittal, for 12 watts output.

Your battery is not charging back up until you see a minimum of at least 13.8v or more. 13.7V is barely a "maintenance" charge, more a power supply voltage as far as your battery chemistry is concerned with a Pc680 AGM battery installed.

Find some separate rechargeable battery supplies for your GoPro cameras and the other 2 last items, and you should do a little bit better. You probably need to keep engine rpms above 2800 rpm to maintain a positive rate of charge with that Ducati VR. The John Deere model puts out 14.2 to 14.4V and would be a better choice, for replacement.
 
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I was required (in the UK) to set the trim speed at the slowest it would operate.

I think that may be your current issue.

You set the trim speed when the electrical system probably had a higher voltage than what you have now, so the trim motor was set at that time to a minimum torque (speed). Now that you have more electrical load, your overall voltage is lower than it used to be ... so you are now likely getting even less torque from the trim motor causing it to stall out under load.

My guess is if you were to adjust the full up to full down trim travel speed to the Van's suggested 25 - 30 seconds you will likely find the problem will disappear.

Scott makes a good point about checking the voltage with a meter ... PWM circuits will read less than system voltage I forgot about that in my previous post. An O-scope would be helpful if turning up the trim speed does not help.
 
Update

Trim motor runs 30 seconds end-to-end in both directions with engine running.

Conducted 60 minute flight with just standard Vans-supplied avionics on. Couldn’t get the trim to misbehave at any speed.

Battery charging was never better than 13.7V regardless of engine speed or electrical load. The battery was 0.2V higher after landing and switching everything off. So somewhat inconclusive.

I’ve changed the voltage regulator and conducted another short flight with plenty of electrical load. Charging voltage is now 14.0V at any reasonable engine speed. I’m hoping 0.3V is enough to charge the battery in flight.
 
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