# Main board

#### sakis136

Joined Dec 5, 2023
1
Hello everyone. I am very puzzled with a main board from a pellet stove. When on test run is proving 240volts to the fan motor, when it on normal function it provides 160volts instead of 240 (on high speed)(working with levels) lower level is on 140volts. When its on stand by its giving 10volts to the motor but when i disconnecting the motor wiring it goes to 240v. What can be happening? I tried putting a ssr that will give the motor 240volts but the main board will jump the voltage to 80v (the minimum to open the relay) and starts the motor on standby

#### ericgibbs

Joined Jan 29, 2010
18,637
Hi sakis,
It appears the motor drive voltage is a PWM format, for speed control.

E

#### MisterBill2

Joined Jan 23, 2018
17,763
What isthepurpose of this investigation? What is the intended result???

Joined Jul 18, 2013
28,505
When its on stand by its giving 10volts to the motor but when i disconnecting the motor wiring it goes to 240v. What can be happening? I tried putting a ssr that will give the motor 240volts but the main board will jump the voltage to 80v (the minimum to open the relay) and starts the motor on standby
What is the technology of the motor?
What is the size?

#### Tonyr1084

Joined Sep 24, 2015
7,766
Welcome to AAC. Not all of us here are true experts. So I'm going to speak from the position of "Talking About Things I Know Nothing About".

IF the fan is controlled by current then regardless of the current setting - if there is no load then the voltage will appear to be at full supply volts.

To speak with insight and knowledge we'd need to see a schematic or get a very detailed description on how the circuit works.

#### MisterBill2

Joined Jan 23, 2018
17,763
What we can assume, based on the no-load motor voltage of 240 volts, iis either a PWM drive or a drive that is effectively a variable resistance.
And once again I am asking about the purpose of this investigation. I was asked to try to repair a pellet grill drive which was not possible because water had been in the switch-mode power supply for quite a while, while it was powered. The internal corrosion of the copper traces was quite impressive, not even close to repairable.