Need some advice from the electronics gurus here

muncybob

This has next to nothing to do with audio but is electronics related. We have a wood fired boiler in our basement that has saved us a ton of $$ on oil over the last 4 years. It's very easy to operate and I have no complaints expect this...if the boiler is re-started after a short period of time(less than 15 minutes) from the last time it shut off the gasses in the firebox will "explode". I don't see where any damage is caused by this event but I want to avoid it. I need to find something that will prevent the boiler from re-starting within 15 minutes from the last time it shut down. Once that time period has passed I want to be able to start the boiler again(if needed) and once it shuts down again I want it to go into "pause" for the 15 minute time period again. I don't want to spend a lot of $$ on this that could be otherwise used to buy more tunes!

boston1450

Sounds like you need a service man..spend the money & be safe sorry to be so harsh but your family & you are worth more than equipment

cnh

It would seem to me that there must be settings for pressure and water temperature and that a simple adjustment of those would DELAY the time between start-ups if it is on a thermostat? Get it serviced and have the tech reset those so that you don't start up too often.

You could probably do it yourself, if you know where they controls are.

cnh

nspindel

A boiler typically has a top and bottom temperature threshold. A temp at which they call for heat, and a temp at which they stop calling for heat. It heats up to the top threshold, then stops calling for heat. It then slowly cools down to the temp at which it starts calling for heat, and so the cycle goes. The farther apart those two settings are, the longer the time the boiler is resting between cycles. But if you don't know what you're doing, you definitely want a pro making the adjustments.

dkg999

Is there a gas igniter for the wood fire?

muncybob

A little better explanation is needed. The boiler has what's known as a cycle timer on it. The function of this timer is to "turn on" the boiler which simply stated means to start up the down draft fan of the unit to get the hot coals in the firebox going and thus the fire is re-ignited. The reason for this timer is to not let the fire totally extinguish during the times of the year when temps are fairly mild outdoors and the call for heat is not frequent enough to keep the fire going based on the aquastat settings. The cycle timer is a simple mechanical device that has prongs set at certain intervals that turn on the boiler for a few minutes and then turn it off again. These 'explosions" I'm refering to(and don't get me wrong, they are not anything that will blow up the house!) happen when concidentally the timer is tripped to go on just after the boiler had shut down from being run by the aquastats.
During the main heating season the cycle timer is not in use as the aquastat settings take care of the process since the call for heat is more often and the high/low settings are far enough apart that there is no chance of the 'explosion" happening.

mrbigbluelight

There are solid state "Delay on Make" and "Delay on Break" relays that are used in refrigeration.

http://www.grainger.com/Grainger/wwg/search.shtml?searchQuery=delay+on+break&op=search&Ntt=delay+on+break&N=0&GlobalSearch=true&sst=subset

When a walkin freezer goes into defrost, the evaporator fan is killed.
This allows any defrosted water to go down the drain instead of being blown out of the drain pan into the cooler.
Coming out of defrost, the compressor starts but there is a delay on starting the evaporator fan. This allows any moisture left on the coils to freeze before the evaporator fans starts, again preventing water being blown out into the cooler.

In your case, if the control output of the cycle timer is run through the "Delay on Break" contacts, the signal from the cycle timer to the downdraft fan could be delayed from 0 to 15 minutes after the boiler cycles off normally (off the aquastat).

During normal operation, the DOB would have no effect on normal operation (running off the aquastat temp sensor).
It would only come into effect AFTER the boiler cycles off normally and AFTER a predetermined (by you) set time.

Relatively easy to do, but if you decide to have someone do it, just realize that it shouldn't turn into a "We have to dig up the foundation, install lightning arrestors, and Simonize your car !" type of deal. : ' )

jbooker82

Explosions are caused by the flammable gasses that build up from heating / burning wood with a lack of oxygen. When the oxygen hits the flammable gasses ignite. Would it be possible to have the top dampner open first to vent the gasses up and out before the bottom intake air vent is opened? Or possibly set it so it doesn't completely cut off all the air that way they don't build up in the first place and they will slowly burn off as they form.

muncybob

I think the DOB is on the right track. Scenario question using the DOB: Let's say the operating temp is reached and the aquastat shuts down the boiler, then let's say 5 minutes later the mechanical cycle timer wants to trip the boiler back on...the DOB will not allow this to happen until my predetermined time of let's say 10 minutes. The cycle timer itself is set to shut down the boiler after a 3 minute burn so will the DOB still send the signal to turn the boiler on since the mechaincal timer has passed the time to shut it down?

jbooker, yes you are 100% correct on why this is happening. This boiler does not have a damper between the unit itself and the chimney, the only damper is on the fresh air intake tube. The fresh air intake is mechanically sealed when the boiler shuts down. I wonder if at shut down there is a way to let the fan stop running but keep the air intake open for a few minutes longer...maybe this would help to burn off those gasses?

jbooker82

Yea having the fan shut off but leaving the fresh air dampner cracked open would allow those gases to burn off or not build up. The gases are methanol vapors comeing out of the wood because there isn't any air for them to burn. If you give it a little draft air they should burn off.