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Go Back   SailNet Community > On Board > Gear & Maintenance > Electrical Systems
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  #1  
Old 04-10-2009
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AH conversion

I have 3 Interstate deep cycle batteries for a house bank. They have 750 cranking with 160 minutes reserve. How does that convert to AH? I checked on the Interstate website but it didn't state anything in AH. I am trying to figure out just how much I have.

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Mike
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What GROUP size are they?
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Old 04-11-2009
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Battery type

According to the website , they are 27M or SRM-27.
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This conversion is very crude. The reserve minutes capacity is the time it takes drawing 25 amps to fully discharge (<10.5 v IIRC). So 25 amps times 160/60 reserve capacity in hours gives 66 2/3 Amp Hours.

These are starting batteries, not really house bank material.
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Old 04-11-2009
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Yes, but the amp-hour rating of most batteries is given for 5 and 20 hour rates of discharge, which the 25 amps is probably much higher than. So, the numbers won't be comparable. The higher the rate of discharge with respect to battery capacity, the lower the effective amp-hours rating will be.

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Originally Posted by gc1111 View Post
This conversion is very crude. The reserve minutes capacity is the time it takes drawing 25 amps to fully discharge (<10.5 v IIRC). So 25 amps times 160/60 reserve capacity in hours gives 66 2/3 Amp Hours.

These are starting batteries, not really house bank material.
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The 25amp draw is MUCH higher than the 20hr. amp draw and can in no way be compared. Example...a typical group 31 battery rated at 100ah's at the 20 hour rate uses a draw of 5amps for 20 hours. Increasing the draw to 25 amps dramatically reduces the amphours available.
Example:
Trojan group31 25amp rating is 190 minutes...79 amp hours. At the 20 hour rate it provides 110ah's...almost 40% more. BUT...this is a TRUE deep cycle battery...not a hybrid starting/deepcycle...so you are probably looking at less of an increase with your Interstates Mike.
Assuming your 160 minute reserve # is at 25amps..the 66amp hours gc1111 quotes might convert to 80-90 amp hours at the 20 hour rate. As such I am thinking you have a group 27 battery?
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