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19-05-2018, 09:25
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#1
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Registered User
Join Date: Sep 2013
Posts: 52
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Mixing battery sizes and proper system.
I'm in the process of upgrading my batteries due to being under house bank amped. I have read many articles and many forum threads, but wanted to ask the smart people my questions directly....so i appreciate bearing with me on a much discussed issue.
First i will replace all the batteries at once with the same brand so i'm not mixing old and new, which i know does not work out.
Ideally because of severe placement issues i want to combine 3 new 165 Victron amp batteries with a 130 amp Victron battery to create my house bank. I have read opinions that say as long as they are parallel your are fine ...yet there are other opinions that say that is a bad idea.
I sort of see the logic that if there all 12 volt and the same age you are ok but obviously want to get this right.
Also I believe that Victron's are considered top tier batteries is that right? They happen to fit.
I'm going to upgrade to a Balmer 165 amp alternator and external regulator to address proper charging.
Lastly i currently have gel batteries and i'm torn between the success i have had with them, and so many people with AGM'S...i get that AGM's have a higher acceptance rate but Believe that GEL's are long lasting and pretty tough.
I currently have a wind charger and 100 amps of solar which i will add to , so that i HOPE to have a comprehensive approach.
There are also an additional group 31 and 3 group 27's for starter, thruster, and the 31 for isolated engine dock and go.
Thanks for any help
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19-05-2018, 10:56
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#2
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S/V rubber ducky
Join Date: Jul 2007
Location: Bahamas cruising currently
Boat: Hunter 410
Posts: 19,395
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Re: Mixing battery sizes and proper system.
Personally I feel that there isn’t a problem connecting old and new, and different size batteries, as long as they are same design and installed in parallel. It’s just harder to determine what capacity you have and probably just have to old school and base it on voltage.
Yeas it’s not perfect, but adding say an older 240AH battery that only has 180AH still adds 180aH to the bank.
I’m sure people will post the buts and what ifs soon for you.
__________________
It is OK if others want to do it different on THEIR boat
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19-05-2018, 11:28
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#3
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Registered User
Join Date: Aug 2012
Location: Maryland, USA
Boat: 58' Sedan Bridge
Posts: 5,176
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Re: Mixing battery sizes and proper system.
Quote:
Originally Posted by blue otter
Ideally because of severe placement issues i want to combine 3 new 165 Victron amp batteries with a 130 amp Victron battery to create my house bank. I have read opinions that say as long as they are parallel your are fine ...yet there are other opinions that say that is a bad idea.
Lastly i currently have gel batteries and i'm torn between the success i have had with them, and so many people with AGM'S...i get that AGM's have a higher acceptance rate but Believe that GEL's are long lasting and pretty tough.
There are also an additional group 31 and 3 group 27's for starter, thruster, and the 31 for isolated engine dock and go.
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Yes, common rule of thumb is same brand, size/shape, type (chemistry), model (dual-purpose vs. deep cycle), age, etc...
But then sometimes ya gotta do what ya gotta do... and if you deviate from rule of thumb, you'll know up front that it's not necessarily optimal... even if you do increase you overall capacity that way.
Your boat.
I suspect folks, especially here, have different experiences with AGMs. I've read they need charging back to 100% often and soon after cycling. If you can do that (like we do) they can maybe last a long time (like ours have). OTOH, if you can't, you'll maybe kill AGMs faster than you can kill flooded lead acid batteries, maybe gels, etc.
Your circumstances.
And then there's the difference between dual-purpose and deep cycle batteries. Some maintain that most 12V batteries, even if labeled deep cycle, aren't. I'm not familiar with the ones you mention... FWIW, three pairs of 6V GC2 golf cart batteries in series parallel would give you 660 Ah capacity, compared to the 625 Ah you propose. There's a taller version that could get you 600 Ah with 4 batteries, if you have height...
What is "isolated engine dock and go" ?
-Chris
__________________
Chesapeake Bay, USA.
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19-05-2018, 11:48
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#4
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Registered User
Join Date: Sep 2013
Posts: 52
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Re: Mixing battery sizes and proper system.
I have a Beneteau sailboat with the dock and go pod. There is a dedicated group 31 that drives the dock and go when engaged
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19-05-2018, 12:25
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#5
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Moderator
Join Date: Feb 2010
Location: La Ciudad de la Misión Didacus de Alcalá en Alta California, Virreinato de Nueva España
Boat: Cal 20
Posts: 18,661
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Mixing battery sizes and proper system.
Quote:
Originally Posted by blue otter
I'm in the process of upgrading my batteries due to being under house bank amped. I have read many articles and many forum threads, but wanted to ask the smart people my questions directly....so i appreciate bearing with me on a much discussed issue.
First i will replace all the batteries at once with the same brand so i'm not mixing old and new, which i know does not work out.
Ideally because of severe placement issues i want to combine 3 new 165 Victron amp batteries with a 130 amp Victron battery to create my house bank. I have read opinions that say as long as they are parallel your are fine ...yet there are other opinions that say that is a bad idea.
I sort of see the logic that if there all 12 volt and the same age you are ok but obviously want to get this right.
Also I believe that Victron's are considered top tier batteries is that right? They happen to fit.
I'm going to upgrade to a Balmer 165 amp alternator and external regulator to address proper charging.
Lastly i currently have gel batteries and i'm torn between the success i have had with them, and so many people with AGM'S...i get that AGM's have a higher acceptance rate but Believe that GEL's are long lasting and pretty tough.
I currently have a wind charger and 100 amps of solar which i will add to , so that i HOPE to have a comprehensive approach.
There are also an additional group 31 and 3 group 27's for starter, thruster, and the 31 for isolated engine dock and go.
Thanks for any help
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I read some time ago one of the upper tier battery manufacturers was happy if if you had same age, type and chemistry but you didn’t need to be all the same capacity.
Rolls/Surrette & Trojan are the top tier last I looked into it. If Victron is top tier it’s probably because they are rebadging an R/S or Trojan battery.
If you got a gourmet regulator to handle the Balmer charging AGMs you might shave 20-30min off of a 5-7hr recharging cycle from 50% DoD. If you don’t normally get to 50% then you aren’t going to save much if anything. If you don’t get a good regulator you run the risk of blowing the alternator by trying to pull more power than it can deliver. I’d go with the Gels. You want a good regulator for that to but it isn’t quite so touchy.
You indicates you had 100amps of solar. I assume you meant 100w because 100a capacity would be 1200w or so which is really big for most boats. You want separate controllers for the wind and solar.
Where are you and what kind of vessel do you have? What’s your current alternator and regulator?
With 625a-hr capacity you have 300+ a-hr available without going deeper than 50%. If you are using 300+ a-hr per day spending on conservation would be more cost effective.
If you are only getting close to 50% every 3rd to 5th day bigger alternator and AGMs really don’t make sense.
My generic advice is to get FLAs or Gels, get a battery monitor (SmartGuage has MaineSail’s recommendation), install about 300w/20-30v solar and an MPPT controller.
I would only start the engine to recharge if I got below 55% first thing in the morning. I would only run it until it got to constant voltage charging and then let the renewables carry it the rest of the way to full.
If I’m getting down to 50% daily then I would look at decreasing consumption and/or adding a battery and another panel. If there’s no room for more solar then I start thinking about a higher capacity alternator.
If I’m only needing to run the motor weekly then I don’t see any reason to upgrade the alternator.
__________________
Num Me Vexo?
For all of your celestial navigation questions: http: fer3.com
A house is but a boat so poorly built and so firmly run aground no one would think to try and refloat it.
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19-05-2018, 13:04
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#6
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Registered User
Join Date: Sep 2013
Posts: 52
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Re: Mixing battery sizes and proper system.
Thanks for the thoughtful reply.....yes a 100 watts of solar not amps. I’m on LI sound. I have 400 amps of house now. I run a fridge, freezer, electric toilets, and Sat tv at night.
There are times of the day when it’s hot and the refrigeration is working hard that I’m burning 15 amps an hour. I have treated my current batteries very well but that involves running the generator at night and every morning and sometimes in the afternoon...I try not to get to 50% discharge.
I have a blue sky monitor that helps me read what’s going on.
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19-05-2018, 13:34
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#7
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Moderator
Join Date: Feb 2010
Location: La Ciudad de la Misión Didacus de Alcalá en Alta California, Virreinato de Nueva España
Boat: Cal 20
Posts: 18,661
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Re: Mixing battery sizes and proper system.
I assume LI Sound is Long Island Sound.
Can you add insulation to the fridge and freezer?
I would expect that while toilettes may require a high current they are very intermittent so the average daily use is pretty moderate. Have you done an energy budget?
Do you use the vessel during the winter or is it pulled out?
If it were me I would try to do multiple energy budgets, for at anchor and underway, and for varying weather conditions.
If you only have very high draw for a few weeks a year requiring daily generator and the rest of the time it's low enough that you only need to run the generator/main engine occasionally then there is still a good argument to bump the solar.
You already have wind. I would bump the solar up to 300w with a good controller and see how often you need to run the main/generator. Solar is the low hanging fruit which is why I start there. Moderator price to install, no fuel costs, no noise issues.
__________________
Num Me Vexo?
For all of your celestial navigation questions: http: fer3.com
A house is but a boat so poorly built and so firmly run aground no one would think to try and refloat it.
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19-05-2018, 13:50
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#8
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Registered User
Join Date: Sep 2013
Posts: 52
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Re: Mixing battery sizes and proper system.
Yes Long Island sound. Beefing the insulation is a good idea no matter what I do. I have used the vessel to go south some years but not always. I’m going to travel this summer to Maine and plan on just floating around for a month.
I have not done an exact detailed energy budget but with my current Blue Sky , I know I use 250 amps easily. So the 400 house bank seems small.
I think adding more solar needs to be part of my solution
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19-05-2018, 13:56
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#9
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Registered User
Join Date: Aug 2017
Location: Kentucky
Boat: 1969 Rhodes 28'
Posts: 307
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Re: Mixing battery sizes and proper system.
In general, if all the batteries are 12 volts and in Parallel, you can mix and match.
Any batteries in series (like two 6 volt units) should be identical.
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20-05-2018, 03:21
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#10
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Senior Cruiser

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 47,083
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Re: Mixing battery sizes and proper system.
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"
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20-05-2018, 12:35
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#11
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Marine Service Provider
Join Date: Sep 2008
Location: Victoria B.C.
Boat: CS27
Posts: 2,867
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Re: Mixing battery sizes and proper system.
Quote:
Originally Posted by Adelie
Rolls/Surrette & Trojan are the top tier last I looked into it. If Victron is top tier it’s probably because they are rebadging an R/S or Trojan battery.
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Victron batteries are made in Europe. Definitely not Trojan or Rolls/Surrette.
Their gel batteries are probably made by Sonnenshein. Not sure who produces their Agm batteries. Victron batteries do not follow the North American sizes - eg group 24,27, etc. They follow European battery sizing.
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20-05-2018, 14:39
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#12
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Registered User
Join Date: Aug 2013
Location: Sharbot Lake Ontario
Boat: Albin 25
Posts: 187
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Re: Mixing battery sizes and proper system.
just to confirm/hijack: I have 2 GC batts in series. I needn't over-worry about adding 2 more in parallel a year later should the need arise?
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20-05-2018, 14:41
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#13
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Registered User
Join Date: Aug 2017
Location: Kentucky
Boat: 1969 Rhodes 28'
Posts: 307
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Re: Mixing battery sizes and proper system.
Each series string should be matched.
Be clear on the difference of series versus parallel.
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20-05-2018, 14:46
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#14
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Registered User
Join Date: Aug 2017
Location: Kentucky
Boat: 1969 Rhodes 28'
Posts: 307
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Re: Mixing battery sizes and proper system.
Series vs Parallel
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20-05-2018, 18:03
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#15
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cruiser
Join Date: Jan 2017
Boat: Retired from CF
Posts: 13,302
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Re: Mixing battery sizes and proper system.
Better if all batts in a bank are identical including mfg date.
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