Have my Pulse Pro VDP monitor installed & my VDP is oscillating way too much, any ideas?

So I’m running a Gorilla Grow 5’ X 9’ tent with 2 X KIND LED X2 Commercial LED fixtures with a 14,000 BTU portable dual hose AC to keep the CO2 in the tent & a dehumidifier & 2 identical humidifiers. My daytime VDP is oscillating by 22%, that’s a bit much… I was really hoping to get it dialed in as close to optimum as possible to increase yield. I’m using Inkbirds to control the temperature & humidity in the tent, the temperature Inkbird feeds the trigger coil of an external relay box I built so the Inkbird didn’t have to try to power the 14k BTU. The VDP oscillates ~20-22% from 1.4 kPa - 0.7 kPa, if anyone has any ideas please let me know!

Here’s a link to view an hour of my day cycle:

I’m quite surprised I don’t really see this same question asked anywhere else, I can’t be the only person having this problem…

By the way, to the people at Pulse, I absolutely love this device! If I could make any changes, maybe a rubber case to protect it, $500 is quite a bit to drop & worry about dropping it. Also, it’d be an awesome addition if I the graph was able to plot a horizontal line for my VDP goal setting & maybe additionally a horizontal line for my VDP high & low limits & those select switches to turn these lines on & off. Perhaps the ability to plot the same lines for Temperature or humidity or whatever variable someone is trying to work out, it just seems like it’d be quite handy to me. Otherwise, it’s an amazing device, I love being able to see my lights spectrum.

1 Like

Welcome EnerGeTix!

So I’m looking at your graph and it looks like the temperature stays within 1% or so, which is great. However the humidity is really spikey, which looks like its driving your swings in VPD.

My first question is what is driving those those spikes? It seems that when the heat begins to decline you are dropping approx. 20% RH in 3-4 minutes. Thats pretty quick in my experience. I’m getting the indication that you are not using any exhaust, but using a humidifier, dehumidifier, and air conditioner to control your environment. Is there anything else I’m missing?

When I need to control the humidity in my tent, I exhaust my tent. I noticed quickly that if the exhaust fan was turned up too high, I would see huge swings in RH (similar to what you are seeing but not as bad). My solution was to turn the equipement speed down. Now instead of turning on high speed and venting for 15 seconds, and dropping 7-8% RH, it would turn on medium-low speed for 30+ seconds and dropping only 2-3%. I’m guessing you aren’t venting cause you want the CO2 so this doesn’t solve your problem, but I’m guessing your problems solution could be similar…

My guess is that drop in humidity coincides with the AC turning on? Air conditioners do a really good job of dehumidifying the air, and if that is the culprit for dropping your RH 20%+ in a few minutes, I’d guess its just too powerful. While I don’t have the expertise myself, it’s my understanding that oversized AC’s do a poor job of maintaining environment and are inefficient since they are constantly going off and on. If you can make the conditioned air come out warmer, or dial down the speed that might help. Ideally this would slow down the rate of cooling as well as the dehumidification. If adjusting the temp/speed isn’t doable/working, you could also try adjusting the thresholds for on/off if possible. While you may want it to stop dehumidifying at X%, but if you end up with X minus 10%, then maybe you could set your turn off point higher, so it doesn’t end up 10% lower, but maybe 4-5% or whatever is acceptable for you.

Hopefully this helps :slight_smile:

1 Like

Thanks for the feedback.

I know inkbirds support variable “deadband” settings, so you could try tightening those up, so that the AC kicks on sooner (but that will be more AC cycles).

One thing is that the 14k BTU AC might be way overkill for the tent, is there a way you can reduce the power of the AC?

Also, you might have too many things happening at once with the AC, humidifier, and dehumidifer.

Does your AC & dehumidifier kick on at the same time? Perhaps expand the control bands for the dehumidifier & humidifier a bit, or instead of letting the inkbirds control them, have them running at a low and steady setting.

Can you share some details about how you have the control parameters set up?

Wow monstermash, thank you for the fast & detailed reply! You’re absolutely right, I don’t know why I didn’t consider the possibility that the AC is too powerful. I only have 1 of the lights on at 750W at this time because I ran into problems with my clones & didn’t get nearly as many as I usually do, it’ll likely run different when I have both lights on. You are correct that I’m not venting the tent due to CO2, hell the AC has a leaks I’m trying to plug, it pulls additional air in the bottom, designed that way, but it pulls some CO2 out now.
Yeah, so that’s what I’ll try next, reducing the speed of the fan in the portable AC is about the only variable I can change other than deadband settings of Temperature Inkbird. I’ve already tried changing the RH Inkbird & nearly eliminating deadband, but the AC is just too efficient at removing humidity from the air & it pulls it down by ~20% as you indicated. I’ll give it a shot & let ya know.

1 Like

I’m only running 1 of the 2 lights currently which exacerbates the issue I’m sure, I’m going to try dropping the fan speed of the AC to medium or low.

If all cycles in a repetitive pattern, AC drops RH, humidifier kicks on to bring it back up. AC kicks off, humidifier catches up, everything kicks off for a few & all is well, then humidity slowly creeps back up, kicking on dehumidifier, creating heat, kicking on the AC. Dehumidifier kicks off because AC pulls RH down. Rinse & repeat, so not really too much going on, just need to slow down the AC.

RH Inkbird was originally set for 5% on humid & dehumid controls. This was the first thing I tried, went down to 3%, even 1%. I honestly don’t recall exactly what it did but it didn’t solve the issue. At the time of the graph I shared, the Inkbird deadband is set for 2% on both humid & dehumid, I may change the dehum one back to 5% so it can sit longer after everything catches up & sits for a bit.

Thanks for your assistance, I’m really enjoying this Pulse device so far. If I can get this dialed in, and my plants blow up & I get a bigger yield than normal, I’m going to be so friggin’ exited!
Any numbers on the % increase in yield when VDP is dialed in correctly? I saw somewhere it can be the difference one would experience between running CO2 & not running it!

Oh, almost forgot, deadbands of Inkbirds:
Temperature Inkbird is set at 3ºF for both heating hysteresis temp & cooling back temp, so +/` 3ºF basically.

RH Inkbird currently at +/- 2% RH, so humidifier & dehumidifier deadband at 2%, awfully tight.

I also want to add that so far I love the Journal function of the app! You guys really have thought a lot of this out. What about a water sensor for that external jack, like looking for a water leak, you could offer a probe of some kind that sits below your mechanic devices to watch for a water leak. I’m using a Govee type device, but it’s probably a sensor nearly every indoor grower could use. I’ll add it to the wishlist.

Seems like a good plan. Where is your temp sensor that triggers the AC located?

You can get an approx 20% yield gain for keeping VPD in the ideal range, and maybe another similar gain for keeping VPD variability +/-0.4kPa (so in veg running things between 0.8kPa and 1.2kPa the whole time).

Here’s a couple of charts from my vpd guide (first is tomatoes, 2nd is lettuce, so to be taken with a grain of salt!)


Thanks for the detailed response & the numbers, 20% is pretty impressive for sure.
I drew out the layout of the 5x9 tent on my phone, the sensors are at the X in the top right corner, the AC has a 16" fan above it, the oscillating portion doesn’t work anymore so it just helps distribute the cold air from the AC across the tent, it sorta flows in a counter-clockwise manner I believe, so I put the sensors where it take the longest to get to them at the height of the canopy. There’s a 16" vertical & horizontal oscillating fan right above the ‘sensor array’ so it’s not a still corner by any means.

I don’t have enough lead length to get the Inkbird sensors to the middle of the tent unless I completely relocate my Inkbirds. Appreciate your assistance by the way.

1 Like

Any of that advice help? Hope you got it dialed in :v:

1 Like

It still oscillates… The best I can do until I change the AC to something else is try to center everything so the average VDP is correct, it’s my only option at the moment. Thanks though. Sorry for the late reply, haven’t been on here for months.

Another factor I hadn’t previously considered is perhaps is because the portable AC is designed in a way that is uses the humidity in the air to create coolness. I’m not an HVAC specialist so I don’t know if all AC units do this, but I suspect home furnace units & window ACs do not do this but I’m not sure.

I know there’s times if the humidity is too low in the tent, this portable e AC literally cannot cool as far as I have it set for in a timely fashion while the lights are on. It’ll just run & run, struggling to reach the temperature.

1 Like