hello everyone and welcome back to

another service video

today we're going to talk about tracking

down a ground fault on a vfd in one of

our control packages

be sure to follow all safe work

practices especially the use of ppe

all circuits should be de-energized

prior to any wiring or service

remember many of our controls will have

more than one circuit that will need to

be turned off

after de-energizing the circuit verify

that the circuit is dead

then lock out and tag the breaker

so first let's talk about what the fault

is a ground fault simply means that

there's a short to ground

somewhere between the vfd itself and the

motor that it's supplying

so if you notice here i have this vfd

and it's flashing sp

sp is start pending is what sp stands

for and that's a four minute delay

so what this vfd is gonna do it's gonna

try to start goes into fault

it starts flashing sp four minutes later

it's gonna try to start again

on its own it's going to try to send

power to that fan if it faults again

it's going to go do this four minute

delay if it does that four times in a

row

it eventually goes to fault lockout and

the display will say

lc so if you ever get to somewhere and

you have a vfd where it's displaying lc

that's fault lockout

the only way to reset a lockout is to

cycle power to the drive

so while it's showing sp on the drive

you can push the stop button

and it'll show you the fault fof1 is a

ground fault

so if you look in the lens manual it's

going to say ground fault

so now let's talk about how to find that

fault where it is in the circuit

start by getting the vfd to a stopped

condition or powered down

then turn off the disconnect to the fan

that the vfd is controlling

now restart or power up the vfd if the

vfd starts

to count up normally that means that

your short exists

between the disconnect and the motor on

the fan

if however you get the fault again the

short is before the disconnect

if this is the case then stop the vfd as

before disconnect the load wires from

the vfd

or at the quick disconnect in the

control package and restart the vfd

if the vfd starts up normally then you

know your short is between the vfd

and the fan disconnect if the ground

fault still exists

the fault is in the vfd and the vfd

should be replaced

following these simple steps will help

you find the ground fault in your fan

circuit

and save you time and frustration if you

have any questions about this video or

any of our products feel free to contact

our tech support team

thanks for watching

welcome everybody to another service

video

today i'm going to talk about the modbus

network that we use here in our control

packages

we're going to talk about what it is how

it works and some common faults that we

see here in the tech support team

be sure to follow all safe work

practices especially the use of ppe

all circuits should be de-energized

prior to any wiring or service

remember many of our controls will have

more than one circuit that will need to

be turned off after de-energizing the

circuit

verify that the circuit is dead then

lock out and tag the breaker

first let me explain what a modbus

network is a modbus network is an

internal device network where you have

several devices all connected together

daisy chained together with cat5 cable

all this blue cable here

so for example we have three vfds so

because they're all daisy chained

together

on one network with one single cable

each device has to have its own unique

address

so for example we have two exhaust fans

and a supply fan vfd

the two exhaust fan address will be 11

and 12.

supply fan addresses start at 21 and

then all the other devices on the

network

hmis core panels filter monitors

each device is going to have to have a

unique address to all work on this

network so every modbus fault

is a communication problem so one of

three things is going to happen

either the circuit board is looking for

a device it's programmed to look for a

device that doesn't exist in the network

maybe your device is powered down you

haven't plugged it in something like

that

you have a device that's in a fault

condition that'll cause a modbus fault

or this circuit board controls these

devices it tells these devices what to

do

if this board is telling this device to

do something that it cannot do

because of an internal limit that'll

cause a modbus fault

just remember that any modbus fault is

going to take

about 10 to 20 seconds to show up and

it's going to take just as long to go

away

so when you're troubleshooting you're

tracking down a modbus fault

you kind of have to work at a slower

pace because the modbus fault you make a

change in the network say you change

this cable you suspect this cable is bad

you plug in a new cable

the fault doesn't go away right away oh

now you're frustrated because well that

didn't fix it

just give it a little bit of time give

it 10 20 30 seconds

for the fault to clear itself because

this board is going out and pinging each

device periodically and that's when it

clears and that's when it shows up

so again work at a little bit slower

pace because the faults take a long time

to show up and a long time to go away

so now i'm going to talk about some of

the most common faults that we see

here at tech support especially on new

startups new jobs as soon as you apply

power and vfds are powered up you get

some faults these are the most common

ones

the most common is just a general modbus

fault hmi is going to say modbus fault

and give you a device number you know

vfd number one

vfd number two something like that and

then you have to track it down you have

to figure out where the fault's coming

from

the most common problem a lot of times

is the vfds aren't powered up

you've powered up the board you've

applied power to the circuit board but

the vfds are not

powered up that'll cause a modbus fault

because again it's a communication

problem

the board is looking for a device it

can't see because it doesn't have any

power

so make sure all your vfds are powered

up

the other most common problem is after

tested balance you have a test and

balance agent come in

he'll set the fan speed we set fan speed

on the

display on the front of the hood through

this circuit board

there are limits inside the vfd and we

do that because we're using direct drive

fans the fan wheels have a

specific maximum rpm that they can't

exceed

that rpm is calculated and we put a

limit in the vfd for max speed

well the board doesn't know what that

limit is you can set the board

above that limit so when you do that

and you push the fans button you tell it

to run at high speed you'll get a modbus

fault

and it just says modbus fault exhaust

fan vfd number one

something like that the problem is is

that the board

is asking the vfd to run at a higher

speed

than the vfd is allowed to run that'll

cause a modbus fault and that trips

people up all the time we see it most of

the time after

the air balancer is finished the last

common problem that we see

at startup on a new job is when you have

a vfd that's mounted in a fan

so this is our supply fan vfd for

example this could be mounted

in the dedicated makeup air unit on the

roof

in the fan if that's the case

you have to run a cat5 cable from this

vfd

up to the roof to the one that's mounted

in the fan that gets missed a lot

and so the guys will turn everything on

and have a modbus fault supply vfd

and that's usually the most common

problem the other common problem we see

is when you make up a cat5 cable in the

field when you're actually making it up

putting the ends on crimping it down

if you get two wires reversed something

like that that'll cause a modbus fault

so get yourself a cheap tester it's

available at all the big box hardware

stores

it's a good little investment to be able

to test that cable after you've done it

avoid a lot of problems

the last problem i want to talk about is

a possible address

problem where you have a vfd that's

addressed wrong

the time that we see this and we get

most phone calls in is

when a vfd has gone bad electrician

whoever

service guy has ordered a new vfd

installed it

now he has a modbus fault as soon as he

powers it up gets a modbus fault

why am i getting this fault a lot of

times when you order these vfds

if we don't have really good details got

duplicate vfds the factory doesn't know

how to program they don't know what

address to program it for

so a lot of times they'll come out

programmed for it

at address 11 or exhaust fan number one

maybe you replaced exhaust fan number

two so now you have two vfds with the

same address 11

that's going to cause a modbus fault so

again

if you suspect that it's an address

problem contact the tech support team

for help on changing the address it's

kind of a little bit of drawn out

process getting into the vfd

so i recommend that you contact our team

for help with that

the next modbus fault that i'm going to

talk about is when the device is

actually in a fault condition

some of the most common ones we see

especially at startup brand new jobs

most common is the fault number eight so

you get the

everything powered up push fans button

fans start coming up

and boom you have an hmi just showing a

modbus

fault fault number eight exhaust vfd one

something like that what a fault number

eight is it's an overload fault

it just simply means that the motor just

pulled too many amps it's like an old

you know mechanical overload so you have

to troubleshoot the motor

why it's pulling too many amps it could

be that the rotation is backwards

that's the most common problem is

backwards rotation remember you have to

check the rotation on the fans visually

you can't just test that it's moving air

in the right direction they'll move air

in the right direction even when they're

running backwards but they pull really

high amps

the next problem could be that you have

the wrong fan on the wrong vfd

so say you have two fans you have a one

horsepower motor and a two horsepower

motor

you put the two horsepower motor on the

one horsepower vfd that'll cause them

oddball's fault

because you can't run a larger motor

than the vfd is rated for

the next most common problem that we see

not as common as

fault number eight but it's fault number

three number three is a ground fault

to track down a ground fault there's a

few steps that will help you kind of

narrow down where the ground fault was

going to be

ground fault is simply just a short to

ground a direct short to ground

between the vfd and the motor it's

controlling

so we suggest you watch our video on

troubleshooting ground faults it's going

to give you a lot more detail on how to

troubleshoot narrow down where that

fault is

so you're not having to look through the

entire circuit the last two most common

faults that we see

maybe not so much as startup but you

know after long term is a fault number

four

and a fault number seven fault number

four

is a temperature fault that simply means

that the drive itself is getting too hot

and it will shut down and give you a

show you display a fault number four on

the hmi

things to look for is some of these

drives the bigger drives and three

horsepower or larger i believe

they get an internal cooling fan so make

sure that fan is running

the other thing to check is make sure

this cooling fan the cabinet fan is

running

that the filter on top is clear you

don't have any paper sitting up here

no dust anything like that and lastly

that all the

cabinet vents are clear so that you're

getting good airflow through this

cabinet to keep those drives

cool and then the last fault we'll talk

about is the fault number seven

number seven is uh low dc bus voltage we

get that call

a lot and it mainly comes after

say there's a thunderstorm that rolls

through the area and the restaurant

experiences a power failure in the

middle of dinner service for example

when the system comes back up a lot of

times they'll show us fault number seven

and it's a low dc bus voltage it's an

internal fault to the drive

all it simply means is that the line

voltage to the drive

dropped below a certain point which is

exactly what it did when the power went

out so to clear the fault

all you have to do is cycle power to the

drive at the breaker panel

so you turn the breaker off wait for

this display to go blank

as soon as it goes blank you can turn

the breaker panel back on

this drive will reset and you should be

good to go that should solve this fault

number seven so there are other devices

and situations that can cause a modbus

fault but just remember a modbus fault

is always a communication fault

so the troubleshooting is going to be

basically the same if you have any

questions on this or any of our products

feel free to contact our tech support

team thanks for watching