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GSA28 in 24V system and trim

kaa

Well Known Member
Hi all,

I bit unusual setup, but how do I connect GSA28 to Ray Allen Trim in a 24V system? I can set up "trim in" wires to be 12V levels, so that when the servo is in a pass through mode the trim works correctly, but I'm a bit unclear on what happens when the GSA28 controls the trim.

I see there is a "Trim Motor Voltage" setting for the GSA28. Does it mean that when it is set to 12V the GSA28 will downregulate 24V input to 12V for the trim motor outputs?

In particular this page is confusing: https://support.garmin.com/en-US/?faq=JgjMM09KZw3qmcMthIHNw9. It says "The DC trim motor connected to the GSA 28 should be rated for the full power supply voltage being used to power the GSA 28. If the GSA 28 is connected by a 24-28V power input, the trim motor must also be rated for 28V". What does the "Trim Motor Voltage" setting do then?

Thanks,
Konstantin
 
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The GSA uses pulse width for driving the trim motor (variable speed). The PWM signal runs at 50% duty cycle when selected 12V vs 24V, but still pulsing at the servo's voltage (24V in this case). That's why the note is there, as damage to the trim motor could happen.
 
Trim Motor Voltage

Hi all,

I bit unusual setup, but how do I connect GSA28 to Ray Allen Trim in a 24V system? I can set up "trim in" wires to be 12V levels, so that when the servo is in a pass through mode the trim works correctly, but I'm a bit unclear on what happens when the GSA28 controls the trim.

I see there is a "Trim Motor Voltage" setting for the GSA28. Does it mean that when it is set to 12V the GSA28 will downregulate 24V input to 12V for the trim motor outputs?

In particular this page is confusing: https://support.garmin.com/en-US/?faq=JgjMM09KZw3qmcMthIHNw9. It says "The DC trim motor connected to the GSA 28 should be rated for the full power supply voltage being used to power the GSA 28. If the GSA 28 is connected by a 24-28V power input, the trim motor must also be rated for 28V". What does the "Trim Motor Voltage" setting do then?

Thanks,
Konstantin

Hi Konstantin,

If you are using a 12V DC Trim motor, you cannot provide 28V to the GSA 28. When autotrim is in use, the GSA 28 is providing voltage to the trim motor directly, so the power input for the autopilot servo must match that of the trim motor.

If you have a 28V system, which would allow you to use a 28V DC Trim motor, you would set Trim Motor Voltage to 28V. If using a 12V system, you would set Trim Motor Voltage to 12V.

Thanks,

Justin
 
Thanks for the responses!

If you are using a 12V DC Trim motor, you cannot provide 28V to the GSA 28. When autotrim is in use, the GSA 28 is providing voltage to the trim motor directly, so the power input for the autopilot servo must match that of the trim motor.

If you have a 28V system, which would allow you to use a 28V DC Trim motor, you would set Trim Motor Voltage to 28V. If using a 12V system, you would set Trim Motor Voltage to 12V.

This doesn't quite make sense to me. If what you were saying was true, there would be no need to have the "Trim Motor Voltage" setting. If the trim motor voltage always matched the GSA 28 input voltage rating, then GSA 28 could just PWM the input voltage, and the setting wouldn't be necessary.

What Brad said above makes more sense to me (that PWM duty cycle is reduced by 50% when GSA is fed 24V and the Trim Motor Voltage is set to 12V). Could you confirm that this is what happens?
 
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