Reply
 
Thread Tools Search this Thread Display Modes
 
Old 01-23-2020, 02:01 PM   #1
Member
 
City: Halifax, Nova Scotia
Country: Canada
Vessel Name: Foto
Vessel Model: Mainship Pilot 34
Join Date: Feb 2019
Posts: 14
8D vs Type31

Can someone tell me what the difference is between a 120AH 8D and a 120AH Type 31 other than size and weight? Just about to do a battery purchase and it seems to me Type 31 would be the way to go to get more AHís in the same space as my 8Dís are taking up now.
__________________
Advertisement

JamieM is offline   Reply With Quote
Old 01-23-2020, 02:07 PM   #2
Guru
 
DavidM's Avatar
 
City: Litchfield, Ct/Punta Gorda, Fl
Country: USA
Vessel Model: Atlas Pompano 23
Join Date: Aug 2012
Posts: 5,134
I don't know where you are getting your AH numbers. Most 8Ds if they report AH capacity at all, report 200 amp hours. Group 31s are usually 100 amp hours. Neither are particularly good house batteries if that is what you are after.

Two golf cart batteries wired in series give about 220 AHs, are true deep cycle designs and take up the same room as an 8D.

David
__________________

DavidM is offline   Reply With Quote
Old 01-23-2020, 02:16 PM   #3
Member
 
City: Halifax, Nova Scotia
Country: Canada
Vessel Name: Foto
Vessel Model: Mainship Pilot 34
Join Date: Feb 2019
Posts: 14
Quote:
Originally Posted by DavidM View Post
I don't know where you are getting your AH numbers. Most 8Ds if they report AH capacity at all, report 200 amp hours. Group 31s are usually 100 amp hours. Neither are particularly good house batteries if that is what you are after.

Two golf cart batteries wired in series give about 220 AHs, are true deep cycle designs and take up the same room as an 8D.

David


Thanks for the quick reply. My boat came with two 8D 120AH LA batteries. My previous boat was equipped with Type 31 120AH LA batteries. I guess the answer to my question is 120AH is 120AH whether a large or small battery. I have to change out my two 8Dís which are in two banks and used for starter or house since each bank is the same. I was thinking 3 or 4 Type 31 AGMís in each bank.

I know this subject has been discussed a lot but was mainly interested in the size and weight difference between the 8D and the Type 31 yet producing the same AH.
JamieM is offline   Reply With Quote
Old 01-23-2020, 03:17 PM   #4
Guru
 
DavidM's Avatar
 
City: Litchfield, Ct/Punta Gorda, Fl
Country: USA
Vessel Model: Atlas Pompano 23
Join Date: Aug 2012
Posts: 5,134
I suspect that 120 AH on your 8D label is bogus. No 8D will be 120 AHs. It is almost twice the weight as a Group 31. Weight equals capacity.

So it sounds like you have an opportunity to upgrade your batteries and do it right. A Group 31 starting battery will start anything up to 6 liters. If you have a bigger engine then maybe an 8D is warranted. And a Group 31 won't kill you getting it in and out next time. Get rid of those 8Ds and just do it once and be done with it.

But set up your house battery bank with two GC batteries wired in series. They will last much longer than a run of the mill 8D.

David
DavidM is offline   Reply With Quote
Old 01-23-2020, 03:26 PM   #5
Guru
 
Alaskan Sea-Duction's Avatar
 
City: Inside Passage Summer/Columbia River Winter
Country: USA
Vessel Name: Alaskan Sea-Duction
Vessel Model: 1988 M/Y Camargue YachtFisher
Join Date: Jul 2012
Posts: 5,130
Get rid of the 8D. I am assuming you have a diesel engine? If so buy 2-Group 31 and tie them in parallel. (Positive to positive). No worries. I did this a few years ago on the stbd engine and then the port side a few weeks ago. No more 8Ds!!
Alaskan Sea-Duction is offline   Reply With Quote
Old 01-23-2020, 03:54 PM   #6
Senior Member
 
obthomas's Avatar
 
City: Seabrook Texas
Country: USA
Vessel Name: TheVenture
Vessel Model: 1985 Bestway Labelle Sundeck 40ft
Join Date: May 2013
Posts: 492
8D batteries are huge and heavy and have a lot of amp hours. If this is what you had replace each 8D with a pair of GP31s in parallel. If you are old like me the GP31s are so much easier to man-handle in and out of the boat. 8Ds and GP31s are good starting batteries and are not deep discharge design. Not very good as house batteries. Take a look at the newer OSGR starters because for less than a couple hundred dollars you can buy a new offset gear reduction starter that doesn't need the amps of an 8D. You may be surprised that you can get by with just 1 GP31 in place of the 8D.
obthomas is offline   Reply With Quote
Old 01-24-2020, 07:50 AM   #7
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 20,058
Every LA battery can be judged by its weight of lead. If your 8D is heavier than 2 grp 31 , it will have more guts .


This assumes you are comparing deep cycles or starts , not the silly "marine" rated batts that are best at what they are created for
.Hours pulling a 20 ft boat with a 12v trolling motor and having enough left to start an engine.
FF is offline   Reply With Quote
Old 01-24-2020, 08:11 AM   #8
Guru
 
ranger42c's Avatar
 
City: Maryland
Country: USA
Vessel Model: 42' Sportfish
Join Date: Aug 2013
Posts: 4,846
Quote:
Originally Posted by JamieM View Post
Thanks for the quick reply. My boat came with two 8D 120AH LA batteries. My previous boat was equipped with Type 31 120AH LA batteries. I guess the answer to my question is 120AH is 120AH whether a large or small battery. I have to change out my two 8D’s which are in two banks and used for starter or house since each bank is the same. I was thinking 3 or 4 Type 31 AGM’s in each bank.

I know this subject has been discussed a lot but was mainly interested in the size and weight difference between the 8D and the Type 31 yet producing the same AH.

As David has said, 120 Ah for an 8D isn't correct. More like ~245 Ah, IIRC.

That said...

One Group 31 battery with decent cranking amps (CCA, MCA) will start many diesels. Two in parallel will start many more. Three in parallel, especially if they provide very high cranking amps, will start most anything. You can compare youe engine's minimum cranking amp requirements to battery cranking amps... so your looking for the right balance of those features.

And then that said...

If your boat has combined start/house banks (like I think you're describing) with "one 8D per engine and approx half of your house load" -- then it's much like ours. Note that engine starting is all about cranking amps, and that house loads are mostly about capacity (Ah).

Three decent dual-purpose (sometimes labeled "marine" G31s will give you enough cranking amps and slightly more capacity (approx ~300 Ah total for a bank of 3, versus the ~245 Ah 8D you have now) so that'd be a slight improvement. And moving each individual G31 is not as backbreaking as moving a single 8D.

If it helps, I eventually replaced one of our 3xG31 banks with 4x 6V deep cycle (not dual-purpose) "golf cart" batteries, increasing that bank capacity to ~440 Ah. Had to be sure those batteries provided enough cranking amps to start that engine.

If it helps more, the 3xG31 banks have been Odyssey AGMs. Cost an arm and a leg each, but they provide huge cranking amps, decent Ah capacity, and have lasted 10-12 years each bank. AGMs also don't off-gas as much as flooded batteries, and they're basically low maintenance (no periodic watereing, etc.).

If it helps even more, the GCs are Lifeline AGMs. Much more capacity (Ah), not as much cranking amps (but sufficient for our purposes, according to Lifeline), ditto arm and leg, ditto AGM advantages... only had them a couple years now so longevity verdict still out.

-Chris
__________________
South River, Chesapeake Bay
ranger42c is offline   Reply With Quote
Old 01-24-2020, 11:00 AM   #9
Moderator Emeritus
 
ksanders's Avatar
 
City: SEWARD ALASKA
Country: USA
Vessel Name: LISAS WAY
Vessel Model: BAYLINER 4788
Join Date: Feb 2011
Posts: 4,528
The problem with G31 batteries is really not the battery, its that people try to replace their 8D starting battery with a single group 31.

I checked recently and a Group 31 Does Not meet the CCA recommendations for my Cummins 6BTA engines.

That is not to say that it would not work, but it does not meet the Manufacturers Minimum recommendations.

Two Group 31’s in parallel would meet those recommendations.
__________________
Kevin Sanders
Bayliner 4788
Seward, Alaska
ksanders is offline   Reply With Quote
Old 01-24-2020, 11:28 AM   #10
Senior Member
 
obthomas's Avatar
 
City: Seabrook Texas
Country: USA
Vessel Name: TheVenture
Vessel Model: 1985 Bestway Labelle Sundeck 40ft
Join Date: May 2013
Posts: 492
Quote:
Originally Posted by ksanders View Post
The problem with G31 batteries is really not the battery, its that people try to replace their 8D starting battery with a single group 31.

I checked recently and a Group 31 Does Not meet the CCA recommendations for my Cummins 6BTA engines.

That is not to say that it would not work, but it does not meet the Manufacturers Minimum recommendations.

Two Group 31ís in parallel would meet those recommendations.
Consider replacing your starter with a modern OSGR type starter for about $135. Your required CCA requirement will go way down and you may get by with 1 GP31.
obthomas is offline   Reply With Quote
Old 01-24-2020, 11:40 AM   #11
Guru
 
Alaskan Sea-Duction's Avatar
 
City: Inside Passage Summer/Columbia River Winter
Country: USA
Vessel Name: Alaskan Sea-Duction
Vessel Model: 1988 M/Y Camargue YachtFisher
Join Date: Jul 2012
Posts: 5,130
So to settle this. If you have a diesel truck, how many batteries do you have under the hood. My guess, like me you have 2 batteries in parallel.
Alaskan Sea-Duction is offline   Reply With Quote
Old 01-24-2020, 12:12 PM   #12
Guru
 
Rebel112r's Avatar
 
City: Birch bay wa
Country: USA
Vessel Name: Rogue
Vessel Model: North Pacific 42
Join Date: Feb 2013
Posts: 575
Old rule of thumb was 1 cca/ cu in for gas, and 2 for the diesel. I used 1 Crown grp31 w 1100cca for a season, to crank my 2007 5.9 QSB with zero problems.
A charge relay problem, causing my thruster batteries to not get charged made me combine all 3 grp 31s. So thrusters and start are now combined. You can notice a bit of a difference when starting, but 1 will do. Of course if you have a tired engine or starter more batts would be better.
Rebel112r is offline   Reply With Quote
Old 01-24-2020, 12:15 PM   #13
Moderator Emeritus
 
ksanders's Avatar
 
City: SEWARD ALASKA
Country: USA
Vessel Name: LISAS WAY
Vessel Model: BAYLINER 4788
Join Date: Feb 2011
Posts: 4,528
Quote:
Originally Posted by Alaskan Sea-Duction View Post
So to settle this. If you have a diesel truck, how many batteries do you have under the hood. My guess, like me you have 2 batteries in parallel.
I have three diesel trucks, both ford and dodge.

All three of them have two large starting batteries in parallel.
__________________
Kevin Sanders
Bayliner 4788
Seward, Alaska
ksanders is offline   Reply With Quote
Old 01-24-2020, 12:37 PM   #14
Senior Member
 
obthomas's Avatar
 
City: Seabrook Texas
Country: USA
Vessel Name: TheVenture
Vessel Model: 1985 Bestway Labelle Sundeck 40ft
Join Date: May 2013
Posts: 492
My advice is worth exactly what you pay for it.


https://www.elreg.com/blog/why-are-g...rive-starters/


If a older direct drive starter uses up to 50% more power than a modern OSGR starter then if you replace your starter you will need half the battery power.


A new OSGR starter for a cummins 6BTA costs about $135.


If you still want 2 batteries, buy even smaller batteries for the smaller CCA requirement.
obthomas is offline   Reply With Quote
Old 01-24-2020, 12:54 PM   #15
Moderator Emeritus
 
ksanders's Avatar
 
City: SEWARD ALASKA
Country: USA
Vessel Name: LISAS WAY
Vessel Model: BAYLINER 4788
Join Date: Feb 2011
Posts: 4,528
Quote:
Originally Posted by obthomas View Post
My advice is worth exactly what you pay for it.


https://www.elreg.com/blog/why-are-g...rive-starters/


If a older direct drive starter uses up to 50% more power than a modern OSGR starter then if you replace your starter you will need half the battery power.


A new OSGR starter for a cummins 6BTA costs about $135.


If you still want 2 batteries, buy even smaller batteries for the smaller CCA requirement.
Yes, that is interesting, Thanks for posting it!
__________________
Kevin Sanders
Bayliner 4788
Seward, Alaska
ksanders is offline   Reply With Quote
Old 01-24-2020, 02:04 PM   #16
Guru
 
City: Qualicum Beach, Vancouver Island
Country: Canada
Vessel Name: Capricorn
Vessel Model: Mariner 29 - Sedan Cruiser 1969
Join Date: Feb 2019
Posts: 812
Check out the Firefly 31 batteries made by Caterpillar. Read some reviews and hit up some user reviews. These batteries behave much like a Lithium battery and can be taken down to 80 %, some folks report lower. They were designed to be used and abused as Caterpillar was having problems with batteries in their big equipment that sat unused for months then wouldn't start. And vibration was also an issue. So they design and built this new type of battery which doesn't require a complete charge and still keeps going on like the Ever Ready battery:

https://www.emarineinc.com/Firefly-O...oup-31-Battery

This is from an article written by Jeff Cote, a systems design engineer and owner of Pacific Yacht Systems:

"Carbon Foam Batteries. The Firefly Oasis carbon foam AGM battery was developed by Caterpillar to replace the FLA batteries that they were using in their work vehicles. They found that the old battery technology could not, consistently, withstand constant vibration, inconsistent charging or long periods without charging. This new technology is based on the sealed valve-regulated design of a conventional lead acid battery but the negative plate has been replaced by a light-weight, sulfation-resistant, microcell material. One of the biggest benefits of this technology, for boaters, is that the battery can be left in a partial state of discharge (i.e. extended cruising, sitting on a trailer or at a dock without power) and it will not lose any permanent capacity. You simply have to charge the battery and it will return to 100% of its original capacity

If you are looking for the maximum capacity with the smallest footprint that weighs the least, then Lithium batteries (LFP) batteries may be the best choice for you. They are by far the most upfront-cost option but if you use your boat a lot and plan on keeping it for a long time, they will pay for themselves and offer the best value in the long term. A unique characteristic of LFP batteries is that they don’t go through the three stages of charging: bulk, absorption and float. The battery is bulk charged until full (almost no absorption stage required), at which time float voltage and currents are mandatory to prevent over-charging. Note there are very few chargers or alternator regulators that are capable of safely and efficiently charging LFP batteries. If you are designing or implementing a LFP battery system, you will need to choose charging components that are compatible with this technology.

Cost Per Cycle Calculation. This year at the Vancouver International Boat Show, we featured a battery display in our booth that compared the total usable amp hours, weight and cost of FLA, AGM and Carbon Foam batteries. If you are trying to spend the least amount of money possible to replace your battery bank, it would seem to make sense to go with FLA batteries but if you do the math, you can see the value in AGM and Carbon Foam.






Adding Batteries Means Upgrading Your Charger. Another challenge we see is that boaters increase the size of the battery bank but do not increase the size of the charger. One of the most common causes for a battery to fail prematurely is overcharging or undercharging. When sizing a charger, the general rule of thumb is that the charge rate should be at least 10 percent of the total amp hours of the battery bank. For instance, a 400Ah deep-cycle battery bank would require a 40A charger. With large battery banks (800Ah or more at 12VDC), it is worth considering adding a large charger or even a second charger, in parallel, to ensure that the batteries charge at the right rate of charge to prolong battery life.

For FLA, AGM and Carbon Foam AGM batteries, we recommend a smart three-stage charger. These smart chargers detect voltage and resistance from the battery prior to charging and determine which stage to charge, either bulk, absorption or float. They can be left for months at a time and will reliably monitor the state of your batteries. As a reminder, you will also have to change the settings on your charger and your battery monitor to reflect the new battery chemistry.

When a boat has no space for additional batteries, we often recommend upgrading from FLA to AGM. More usable battery capacity with AGMs can translate to increased battery capacity if you keep the same number of batteries or alternatively you can reduce the battery bank size and still have the same amount of usable capacity. If you have been contemplating replacing your battery bank, these new batteries just make sense. Although the upfront cost is higher, the value proposition is unbeatable because of the combination of increased depth of discharge and faster charging.

About the author: Jeff Cote is a systems design engineer and owner of Pacific Yacht Systems, a full service shop delivering marine electrical and navigation solutions for recreational boats. Visit their website and blog for info and articles on marine electrical systems, projects and more: www.pysystems.ca
rsn48 is online now   Reply With Quote
Old 01-25-2020, 09:03 AM   #17
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 20,058
"With large battery banks (800Ah or more at 12VDC), it is worth considering adding a large charger or even a second charger, in parallel, to ensure that the batteries charge at the right rate of charge to prolong battery life."


A different concept might be 2 chargers , each used for 1/2 the battery bank.


Should a cell go bad only 1/2 the batts will be killed by over charging.
FF is offline   Reply With Quote
Old 01-25-2020, 09:16 AM   #18
Guru
 
catalinajack's Avatar
 
City: Edgewater, MD
Country: USA
Vessel Name: Catalina Jack
Vessel Model: Defever 44
Join Date: Nov 2011
Posts: 1,133
Yup. Chevy Duramax.
Quote:
Originally Posted by Alaskan Sea-Duction View Post
So to settle this. If you have a diesel truck, how many batteries do you have under the hood. My guess, like me you have 2 batteries in parallel.
catalinajack is offline   Reply With Quote
Old 01-25-2020, 12:03 PM   #19
TF Site Team
 
FlyWright's Avatar
 
City: California Delta and SF Bay
Country: Sacramento, CA, USA (boat in Vallejo)
Vessel Name: FlyWright
Vessel Model: Marshall Californian 34 LRC
Join Date: Apr 2008
Posts: 12,591
I start two Perkins 4.236 engines from a single Group 31 Costco/Interstate battery somewhere in the 900-950 CCA range. I've never had a problem with the 1st or 2nd engine start. I also have a house bank of 6 GC batts for 660AH that I can parallel if needed. Never have found the need except for once when the boat was launched after being on the hard for over a month with chronic interruptions in shore power. The culprit turned out to be a shorted diode on the port alternator that was slowly draining the start batt when the shore power was off.

I agree that the 8D must be mislabeled. I'm used to seeing about 220AH or more from an 8D. I replaced 2 8D house batts (~450AH) with my 6xGC bank in the same boxes/foorprint and increased my bank size by ~50% to 660AH. Total house bank cost around $600...money well spent.
__________________
My boat is my ark. It's my mobile treehouse and my floating fishing cabin. It's my retreat and my respite. Everyday I thank God I have a boat! -Al

@DeltaBridges - 25 Delta Bridges in 25 Days
FlyWright is offline   Reply With Quote
Old 01-25-2020, 01:23 PM   #20
Veteran Member
 
Screaming04's Avatar
 
City: Vancouver
Country: Canada
Join Date: Dec 2016
Posts: 53
Quote:
Originally Posted by Alaskan Sea-Duction View Post
So to settle this. If you have a diesel truck, how many batteries do you have under the hood. My guess, like me you have 2 batteries in parallel.
This doesnít settle much, two batteries in parallel under the hood is likely because of space limitations...
__________________

Screaming04 is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off





All times are GMT -5. The time now is 08:40 PM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012
×