Aprilaire 8800 eating batteries?

[lonebrave]

I installed an Aprilaire 8800 about two months ago, with the plan to connect it to my Elk once I get it installed. So far, the tstat has been great, except for the fact that it seems to be draining the batteries very quickly. My understanding was that it ran off the 24VAC that was provided to it via the transformer and Aprilaire distribution panel. In the two months that I've had the tstat installed, I've had to replace the batteries twice.
 
I've noticed that the house is overly warm in the morning. I checked the tstat and the display is blank and won't wake up. I've taken the tstat off the wall and put it back on...nothing. I've taken the batteries out and put them back in...nothing. I replaced the batteries with freshly charged ones (Eneloops) and everything works fine. The old batteries are put on the charger and it indicates that they don't have any remaining charge. I haven't put a meter on a set, yet, but will try that next time to see exactly how dead the batteries are.
 
Anyone run into this problem before? Is this normal? I thought the batteries were there to save settings in case the 24VAC power was lost.

 

[Del91574]

Not to over simplify, but have you verified it's getting 24V?

 

[BraveSirRobbin]

This may not be pertinent to your particular problem, but I purchased a plain Jane Honeywell digital display thermostat for my rental home (not even programmable) and received a call from my renter about eight or ten months after installatoin stating that the furnace quit working.
 
Long story short...turned out that the internal batteries needed replacing.  I also thought they were just there for backup and was even more confused when I did detect the presence of 24 volts with my meter when troubleshooting (replaced batteries out of frustration of not finding anything wrong that I could point to).
 
So, I'm wondering if the batteries in this make are indeed the primary source of power.  Do you have a backlight that stays on?

 

[gatchel]

There are some thermostats that claim to be powered on parasitic 24vac power but if the current is too low, they are not.
I had some crappy honeywell T87K1007 units that were hooked up to Taco zone controllers and we had to install a 1000 ohm 3 watt com the common terminal to the W terminal at the zone controllers to get them to work at all, per Honeywell.
 
 
It might be worth giving Aprilaire a call.

 

[BraveSirRobbin]

Interesting.  Wonder if that is the problem with the Honeywell one I mentioned above (couldn't find anything on a quick Google search)?

 

[fcwilt]

Interesting.  Wonder if that is the problem with the Honeywell one I mentioned above (couldn't find anything on a quick Google search)?

 
The closest unit I could find only has access to "parasitic" power as they installation guide says to not connect the C wire.
 
http://www.honeywellstore.com/store/products/honeywell-rth111b-vertical-digital-non-programmable-thermostat.htm
 
So if this is the same unit just in a different configuration then it may well just be running on batteries.
 
And if you have the C wire present then you could get a slightly better unit that will make use of the power from the HVAC - then if it has batteries they should only be for backup.

 

[gatchel]

Remember I was comparing Honeywell experiences to Aprilaire possible causes. They might not have any relevance, just a thought. It never hurts to double check your steps as mentioned above.
 
BSR, My experience was related to one of the round mercury replacements. This one had no display.

 

[lonebrave]

Not to over simplify, but have you verified it's getting 24V?

I originally though it was parasitic 24VAC. I couldn't get anything other than the 'Power outage' message. Then I found a note from Aprilaire that indicates a separate 24VAC source was required by a newer version (which is what I have). I bought the Aprilaire (actually ELK) 24VAC, connected it via the distribution panel, and verified 24VAC at the Aprilaire 8800 mounting plate.
 
I'll try contacting Aprilaire support and see if they can provide any assistance.

 

[BraveSirRobbin]

I'm wondering now if your Aprilaire is drawing so much current that the parasitic supply can't supply it...though you would think a fuse would blow, or you would be reading a greatly reduced value from 24 vac with a meter.

 

[Del91574]

I've seen this happen a bunch of times with transformers in the field....the transformer supplies enough voltage to keep the device(s) running but not enough amperage. Happens often with PTC based devices where they don't completely trip or reset.

Have a site with access control hardware that was doing this.....PITA to find out because it would trip and then would allow most of the devices to be repowered but not all at the same time.
 
May or may not be related to the issue at hand here.

 

[fcwilt]

If the transformer can not supply enough current then voltage must then drop.
 
Now it may be under certain conditions that the current drawn by the load goes from a small amount, that the transformer can supply, to a larger amount, that the transformer cannot supply.
 
At that point the voltage to the load could drop below the required level and the load might malfunction.

 

[Del91574]

If that were true universally per Mr. Ohm, then the meters we were using were not following the same rules.
 
In my case, the voltage was proper but the current did not meet the listed output, even though the system had functioned for years before the issue.....replace the transformers with new units within spec and problem disappeared, no other system component changes.

 

[fcwilt]

Ohm's Law: I = V/R
 
If the V was "correct" and the I was "incorrect" then the R must have changed.
 
It is simply not possible for the transformer to supply the correct voltage but limit the current - it doesn't work that way.
 
Now it is possible that the meter used gave the expected reading but was incorrect - it all depends on the meter and the waveform.

 

[Del91574]

PTC was allowing the voltage through but limiting the amount of current   40 VA rated transformer running about 15 VA. Caused the DC supply to sag and not put out the rated amperage.
 
I understand and use the law often...so often the calcs are in my phone.
 
3 different techs and 3 different meters.
 
The electronics shop at this particular VA put the unit on a scope, so I believe what was seen on it.

 

[fcwilt]

The action of the PTC was "inserting" significant resistance into the circuit feeding the load, there was a resultant voltage loss across the PTC thus leaving less voltage to be applied to the actual load, thus resulting in less current draw.
 
Or to put it another way the transformer was still putting out the rated V (on the transformer side of the PTC) but the effective R was now Rload + Rptc (resistance of load + resistance of PTC) so going back to I = V/R, R goes up, I goes down.