What size Autopilot

donaldm823

LifeTime Supporter
May 21, 2007
148
Cape Coral, FL
for Sean:
I have a 30,000 gal concrete in ground pool and am considering installing one of the new Autopilot Digitals but am confused on what size. I have read that sometimes the size advertised is for a 24hr/day pump running. I only run my pump (single speed) 10hrs per day. So what size should I buy?

Also, I have a 2hp single speed pump with 60ft3 DE filter and 2inch PVC runs to my pool approx 60 ft away. Based on my pump curves I think my pump flow is 120gpm to 140gpm. The Autopilot website says a max of 100gpm. What impact will occur if I install the Autopilot anyway with the SWG loop that is sold with the digital? I do not have enough room to install another bypass loop
 

Poolsean

TFP Expert
Apr 15, 2007
1,462
Ft Lauderdale, Florida
donaldm823 said:
for Sean:
I have a 30,000 gal concrete in ground pool and am considering installing one of the new Autopilot Digitals but am confused on what size. I have read that sometimes the size advertised is for a 24hr/day pump running. I only run my pump (single speed) 10hrs per day. So what size should I buy?
My recommendation is to always get the largest cell you can afford. You will get more chlorine production and longer cell warranty. That would mean the SC-60 cell.

Also, I have a 2hp single speed pump with 60ft3 DE filter and 2inch PVC runs to my pool approx 60 ft away. Based on my pump curves I think my pump flow is 120gpm to 140gpm. The Autopilot website says a max of 100gpm. What impact will occur if I install the Autopilot anyway with the SWG loop that is sold with the digital? I do not have enough room to install another bypass loop
The excess flow will reduce efficiency somewhat. So going with the larger cell will help offset that. You'll be good with the Digital with the SC-60 cell.
Thanks for selecting Pool Pilot.
 

DaveNJ

LifeTime Supporter
May 22, 2007
520
Toms River, NJ
There shouldn't be a problem. I have 2.5"piping. If you go to the "Stickies at the top of the page then "Hydraulics 101" you will see that 2" pipe won't flow 120-140gpm. Very good write up by mas985.
 

JasonLion

TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
37,879
Silver Spring, MD
I would go with the SC-60, but I am sure the SC-48 would be fine. The SC-60 will last longer and so be less expensive in the long run.
 

cliff_s

Well-known member
Mar 28, 2007
93
From experience this can be rather complicated.

The size of the unit depends on the amount of water, the temp. of the water and
how much UV you get from the sun.

In the northern climates the sun angle is lower so the UV is less, also the water temp
is usually lower so there is less chlorine consumption.

The output of the unit can be controlled by the pump run time and the settings on the
unit. You can always turn down a larger unit but you cannot turn up a too small unit.
With ever increasing electricity rates one would want to run the pump as little as possible.
This dictates getting as big a SWG unit as you can afford. The larger units will cost more initially,
but with the reduced pump run time to generate enough chlorine they will easily pay for
themselves in savings on your electric bill.

As you can see the largest unit you can get will be the lowest cost to run.

In AZ where I live the largest unit will just barely make enough chlorine on a 110 deg. day.
The rest of the year it will make too much and the pump run time will have to be reduced
or the unit output turned down.

Cliff s
 

Valera Orlingis

Active member
Sep 4, 2007
28
cliff_s is right, you better off with oversized machine than undersized!
In regards to how big machine do you need, you first need to answer " what is your chlorine demand".
If you do not know, than take recommended average machine and go next size up.
example:
25 gram chlorinator will do:
3000 gallon heated commercial spa OR
30000 gallon private fiberglass pool
It's all about chlorine demand not the volume of the water...
 

donaldm823

LifeTime Supporter
May 21, 2007
148
Cape Coral, FL
Using SC-60 size Autopilot

cliff_s said:
From experience this can be rather complicated.

The size of the unit depends on the amount of water, the temp. of the water and
how much UV you get from the sun.

In the northern climates the sun angle is lower so the UV is less, also the water temp
is usually lower so there is less chlorine consumption.

The output of the unit can be controlled by the pump run time and the settings on the
unit. You can always turn down a larger unit but you cannot turn up a too small unit.
With ever increasing electricity rates one would want to run the pump as little as possible.
This dictates getting as big a SWG unit as you can afford. The larger units will cost more initially,
but with the reduced pump run time to generate enough chlorine they will easily pay for
themselves in savings on your electric bill.

As you can see the largest unit you can get will be the lowest cost to run.

In AZ where I live the largest unit will just barely make enough chlorine on a 110 deg. day.
The rest of the year it will make too much and the pump run time will have to be reduced
or the unit output turned down.

Cliff s
Just to close the loop. I installed an Autopilot Digital with the SC-60 cell in mid-August. I live in the Philadelphia area and my back yard faces south so the pool gets full sun during the day.

In August and early SEP (still 85F-90F days), I was running the cell at 40%, Power 2 (mid power) to maintain 2-3ppm chlorine with CYA only at 30ppm (I elected not raise the CYA to 60ppm per SWG recommendations based on it being near the end of the season). The SC-60 managed well to keep my chlorine level with the 2hp pump running 10hr/day even with CYA at 30ppm vice 60ppm. Near the end of the season (late Sep), I was running the SWG at 40% power 1 (lowest power setting). Please note I have a heater and a solar pool cover, so the pool temps were kept in the 80-85F range.

From all appearances, the SC-60 although bigger than needed, is producing the chlorine amount as advertised and all of the recomendations to buy the next largest cell size for your pool is right on the money. I bought the SC-60 for my 30K gal pool based on my running the pump only 10hr/day. BAsed on my experiences-it looks like 40-50% setting will be the norm, but I will have to raise CYA to manage the direct sun in the Jun-Jul time period. I also found that I needed to use at least a 30% setting on the SWG (with 10hr/day pump run) or my CC would rise during the day-but still it never got higher than 0.2ppm.