Sequencer Relays

Posted by EnigmaPaul@gmail.com on January 4, 2009, 1:30 pm

Hi all,

I have a heat pump with electric heat backup elements in my blower
unit. There are 3 elements in this 15KW unit. Each one has a
sequencer relay. Can sometime describe the function of the sequencer
relays and also the Limit Switches? I believe the sequencer are for
staging the elements so they don't all turn on at the same time but
I'm wondering exactly how it does that.

Also, if my thermostat has only one W output connect to the unit, will
all the elements turn on or will they be staged based on the
temperature conditions at the time?

Thanks!

Paul

Posted by Steve on January 4, 2009, 2:01 pm

> Hi all,
> I have a heat pump with electric heat backup elements in my blower
> unit. There are 3 elements in this 15KW unit. Each one has a
> sequencer relay. Can sometime describe the function of the sequencer
> relays and also the Limit Switches? I believe the sequencer are for
> staging the elements so they don't all turn on at the same time but
> I'm wondering exactly how it does that.

time delays built into the sequencers.

> Also, if my thermostat has only one W output connect to the unit, will
> all the elements turn on or will they be staged based on the
> temperature conditions at the time?

yes, no

> Thanks!
> Paul

Posted by Bipolar Bear on January 4, 2009, 11:17 pm

Typically the sequencers have a bimettalic spring actuated switch that is
heated by your 24V thermostat voltage, unlike a magnetic relay there is an
inherent delay due to the time it takes to heat the bimetal portion--in
practical usage you will find these available having various delay
times...generally from 1/2 up to 2 minutes

> and also the Limit Switches?

The limit switches are for fire prevention due to overheating of the heating
elements from of loss of airflow or from some other cause.

> I believe the sequencer are for
> staging the elements so they don't all turn on at the same time but
> I'm wondering exactly how it does that.
> Also, if my thermostat has only one W output connect to the unit, will
> all the elements turn on or will they be staged based on the
> temperature conditions at the time?

Depends on the sequencers delay spec and the control / HV wiring--for
instance consider the case of 3 each 5 kw strips for a total of 15kw..here,
"staging" can be done by using sequencers all having different delay times
or it can be done by using 3 ea 2pole sequencers all having the same delay
rate, here one pole actuates a 220v heater element with the other pole of
the same sequencer passing 24v onto the next sequencer in your "cascade"..

> Thanks!
> Paul

Posted by Zyp on January 5, 2009, 3:12 pm

Bipolar Bear wrote:

>> Hi all,
>> I have a heat pump with electric heat backup elements in my blower
>> unit. There are 3 elements in this 15KW unit. Each one has a
>> sequencer relay. Can sometime describe the function of the sequencer
>> relays

> Typically the sequencers have a bimettalic spring actuated switch
> that is heated by your 24V thermostat voltage, unlike a magnetic
> relay there is an inherent delay due to the time it takes to heat the
> bimetal portion--in practical usage you will find these available
> having various delay times...generally from 1/2 up to 2 minutes

>> and also the Limit Switches?

> The limit switches are for fire prevention due to overheating of the
> heating elements from of loss of airflow or from some other cause.

>> I believe the sequencer are for
>> staging the elements so they don't all turn on at the same time but
>> I'm wondering exactly how it does that.
>> Also, if my thermostat has only one W output connect to the unit,
>> will all the elements turn on or will they be staged based on the
>> temperature conditions at the time?

> Depends on the sequencers delay spec and the control / HV wiring--for
> instance consider the case of 3 each 5 kw strips for a total of
> 15kw..here, "staging" can be done by using sequencers all having
> different delay times or it can be done by using 3 ea 2pole
> sequencers all having the same delay rate, here one pole actuates a
> 220v heater element with the other pole of the same sequencer passing
> 24v onto the next sequencer in your "cascade"..

>> Thanks!
>> Paul

And not even a thank you for a polite, well thought out, accurate answer.

--
Zyp

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