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15 inch row population setting help

Printed From: Unofficial Allis
Category: Allis Chalmers
Forum Name: Farm Equipment
Forum Description: everything about Allis-Chalmers farm equipment
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=150792
Printed Date: 19 Jul 2025 at 3:23pm
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Topic: 15 inch row population setting help
Posted By: grinder220
Subject: 15 inch row population setting help
Date Posted: 26 May 2018 at 7:14pm
Any one running an allis planter with model 78 units on 15 inch rows. Im trying to figure out which sprocket combination I need to achieve 140k to 160k. My manual only lists 20 to 40 inch rows.


Replies:
Posted By: DougS
Date Posted: 26 May 2018 at 7:50pm
Set the sprockets for about 112,500 with 20 inch rows. Moving to 15 inch rows should give you 150,000.


15 inch rows will give you 4/3 the population you'd get with 20 inch rows.

Posted By: DanWi
Date Posted: 26 May 2018 at 10:11pm
use the 30 inch setting for 75,000 population

Posted By: AC7060IL
Date Posted: 27 May 2018 at 8:54am
You don't need a manual to calculate planter seed population. 

One 15" row is equal to 34.848' / 1000th of an acre. 34.848' x 12"/foot = 418.2''/1000th of an acre. Take 418.2" divided by 140K = 2.98" ~ 3" seed spacing within each row.
Assuming that your AC 78 probably has 18" press wheels that contain the seed plate chain DRIVER sprocket, then it's wheel of 18"x3.14 = 56.52" travel distance/one revolution.  If you take 56.52" divided by 3" seed spacing, then you need 18.84 ~ 19 seeds dropped per each press wheel revolution.  
If your DRIVEN seed plate is a 24 cell type (guessing it is 24, it may be different?) then it will plant that many seeds per it's one revolution. So take 19 seeds per one press wheel rev / 24 cell per one seed plate rev = 0.79 ~ 0.8  sprocket ratio. That means you should have an 8 tooth DRIVER sprocket on the press wheel & a 10 tooth DRIVEN sprocket on the seed plate. (8T/10T = 0.8 sprocket ratio)
If these planter assumptions are close to correct, then these sprocket selections would place it in the 140k ballpark. If your planter's press wheel and/or seed plate vary, then plug & chug your numbers respectfully. Then, test it & adjust if necessary. 

Posted By: Gerald J.
Date Posted: 27 May 2018 at 9:00am
15 inch rows results in exactly twice the population of 30 inch rows, so setting for 70,000 to 75,000 in 30 inch rows planting in 15 inch rows works perfectly and simply. Providing the manual has settings for that range of populations.

Gerald J.

Posted By: DrAllis
Date Posted: 27 May 2018 at 9:15am
74,900 per acre(30 inch rows) takes 10 tooth driving to 15 tooth driven for model 78 AirChamp units with 144 pocket seed discs.   80,200 takes 10 and 14 tooth.   72,200 takes 9 and 14 tooth.

Posted By: grinder220
Date Posted: 27 May 2018 at 12:24pm
Thanks for the replys. I got it figured out. The page I needed was missing in one manual but I found another one I had which has all the information I need.

Posted By: tbran
Date Posted: 27 May 2018 at 2:02pm
just a note - we used to use cotton seed plates for better singulation of soybeans - and I don't even know if they are still around or not - from Agco or at the farm...

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When told "it's not the money,it's the principle", remember, it's always the money..


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