eHERMS efficiency all over the place

BigJay13

I've switched over to eHERMS in 15 gallon pots. Ive got a slotted false bottom in my MT and the blichman autosparge. My current process is to underlet into the MT, stir once, begin the recirculation once I transfer the sparge liquor from the BK to the HLT, wait for the temps to stabilize at mash temp and then start my timer. I flow the wort slower than the videos from Kal and theelectricbrewery during the recirc but otherwise follow those steps. I transfer to the BK at a rate of 1 quart per minute.
I've consistently been getting efficiencies in the high 60's with hydrometer and refractometer. I've tried stirring a lot, stirring a little, and not stirring. I've used rice hulls, I've tried speeding up the recirculation and slowing it down. I usually mash for 45 minutes then increase to 165 over 15 minutes. It usually takes 20 to increase to 165 and I don't start the clock until I hit my mash temp so the total mash is probably longer.
On my old igloo cooler set up I would get mash efficiencies in the low 90's every time. It made it really easy to create recipes. One time on this system I got a mash efficiency in the 80s--it seems to happen on my German pilsner which has a lower SG. Is the reduced efficiency an effect of doing larger mashes? For instance, in my most recent beer the grist was:
21.75 lbs Maris Otter
1.75 White Wheat
.75 C40
1 LB Dextrose
I got a SG of 1055 13.5 gallon pre-boil wort and a mash efficiency of 73%. (total BH efficiency was 68%). In the videos Kal posts and on his website he's getting in the 90s IIRC.
One thing I want to do that I'm wondering if it will make a difference is to create a sparge arm so the mash is being recirculated evenly over the top of the grain bed. I wonder of the recirculating just through the 5/8 hose is causing channeling, then when I sparge the channeling continues. I have never noticed any dough balls when I empty the MT.
Any thoughts are appreciated!

DonT

I have an eHERMS Kal-ish system too. I did a of bunch research to try to understand my system and landed on a few things that work for me. First of all, I don't mash to a specific time, I mash to a particular gravity in the mash. And this depends on the mash thickness I use. I use this chart. So, for instance, if you use a mash thickness of, say, 1.44 qt/lb, the gravity in the mash should land somewhere around 1.085 (I consider this 100%). I use that particular thickness and most times I hit 1.082 after about 60-70 min. I consider the mash done at that point and start my sparge.
I used the hose method for a bit (Kal's way) but found it was digging a hole in the mash and didn't like that. I was still doing some research at the time and happened upon this contraption. Bingo! I'll post pictures later when I get home, but it's made a world of difference.
So when I'm sparging, I transfer to the BK super slow and don't let the sparge water go continuously. I turn it on and off to regulate the water level to just a pinch over the grain. When the volume in the BK gets to about 1-1.5g short of pre-boil I stop the sparge completely and let it draw off what is in the grain mass to achieve my boil volume. I don't want to over sparge and transfer a bunch of thin wort over to the BK.
I hope that's clear! I'll post some pics a bit later.
Cheers!