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Old 10-30-2015, 11:43 AM   #1
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Lightbulb Upgrading to 6V Trojans - Series Parallel Wiring - Battery bank build

The time has come for this project. The plan; upgrade my existing two group 27 batteries to four 6v-Trojan AGM's wired in series parallel to create two big 12v battery banks.

This is how I intend to wire the batteries together:


I'll be moving my batteries from the tongue to the back of the front storage compartment. I might move them elsewhere within the bedroom based on feedback to this post.

For those who don't recall, our bedroom is a little different than the standard queen or twin. The front storage compartment also gained a few inches in depth.


And maybe I can get a few things sorted with your help.

I have read recommendations to use 4/0 class 'K' welding cable between the batteries. As I understand it, the Airstream's current direct connections to the main panel are 6 gauge. Curious if anyone thinks I should upgrade this to 2/0 or 1/0 gauge.

Currently, present between the battery and the Airstream is a 50-amp fuse breaker. Should I consider upgrading this to 80 or 100-amp?

I'll document the rest of this process in this thread as I make progress on the work. This week we are acquiring out batters and cables. And should be getting started next weekend.
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Old 10-30-2015, 11:52 AM   #2
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I have 4 trojans in my golf cart & they are awesome, good luck with your project.
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Old 10-30-2015, 12:31 PM   #3
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Bold,

Since the series/parallel connections are essentially a continuation of the internal battery plate connections, I would go 4/0 for those.

I usually use 4AWG or 2AWG ( depending on run length) for the connections from the batteries to the bus bars. 50 amps for circuit protection is fine.

If you have an inverter. I would upgrade the direct connections for the battery to inverter with 1/0 ( again length dependent) using a 150 amp class T fuse.



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Old 10-30-2015, 01:29 PM   #4
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Bigger, cleanly terminated is better!
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Old 10-31-2015, 10:14 AM   #5
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I recommend you use marine cable rather than welding cable. You can even get it made to order with proper connectors. Such as 1 of many= Custom Battery Cable Assembly Custom Made Genuinedealz.com
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Old 10-31-2015, 11:19 AM   #6
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Thanks. I'm a huge fan of cutting and crimping my own wires so I only have myself to blame for most things. I'm leery of marine as I've purchased some before that were copper coated tin.
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Old 10-31-2015, 11:35 AM   #7
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Belden welding wire is the best bang for the buck. It is very high quality, fine stranded wire in a very durable neoprene/PVC jacket. It solders beautifully!
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Old 10-31-2015, 11:51 AM   #8
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Interested in doing such an upgrade next Spring ourselves, how much weight is added by using 4-6Vs vs. the code 27 batteries? We have 2-12V code 24s in the factory compartments one on each side of the A-frame in the body of the trailer, assuming its for even weight distribution, are you mounting them the same way? Sorry we can't add more towards your decision making process but will follow your thread and use it to plan our upgrade. Good luck and thanks for the idea...
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James and Rebecca
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Old 10-31-2015, 12:26 PM   #9
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We did a similar project almost a year ago, only on a slightly smaller scale. Our 25' Airstream had two size 24 batteries and I switched them to two Trojan 6-volts. Increased capacity from approx. 80 AH per battery to approx 225 AH per battery (now 450 AH total instead of 160 AH total). What an incredible difference as we have solar and do mostly dry camping.
Cable size will be determined in part by how large of an inverter you will be using. We do not use our inverter for the microwave or electric coffee pot, so extra large wiring not an issue. The wire we used earlier for the inverter wiring was MARINE wire.
BATTERY CONVERSION NOTES:
Converted from (2) 24-sized batteries to (2) 6-volt golf cart batteries ((2) Trojan T-105 Batteries 2*($125-$10pickup+$20core)+$21.60 tax).
Items:
1. Replace the 3/8" threaded rod (I think I went from an 8" to a 10", or a 10" to a 12", can't quite remember). Rod replacement is not easy because it is threaded through a nut which is welded on the outside bottom of the battery box, and then the rod is seal welded to the nut. You have to grind off about half of the nut in order to be able to unscrew the existing rod. (With the "undercoating" on the bottom of the battery box this was not evident, so thinking that you could unscrew the existing rod took a lot of time. I called the AS factory and the technicians went out on the floor to examine the bottom of the battery box, but still didn't know that the rod was welded. You cannot use a 3/8" rod coupler to extend the rod, as there is insufficient room for the larger gap required between batteries.
2. The size 24 batteries sit in a plastic shell at the bottom of the battery box. My local AS dealer just removes it and leaves it out, if they do the conversion. For me, I removed it, then cut out both ends of the plastic shell so that the golf batteries would sit on plastic in the bottom of the box.
3. The battery box has to be heightened. This was not a problem for my AS, but if someone has a forward storage outside door, they would have to have the box extended down, instead of up as I did it. I had some 1"X3" oak, so i just made a 2 1/2" extension on the top of the box, and moved the lid up, and it was fine. (Our local AS dealer can fabricate a 2" or 2-1/2" box extension, but opted to make my own.)
4. The two new 6-volt batteries have to be wired in series, instead of in parallel as the 12-volt batteries were.
5. I had to use a pneumatic "nibbling" tool to enlarge the propane tank cover cutout to fit the taller battery box (i.e. trim away 2 1/2" of aluminum to make the propane tank cover slip over the two propane tanks and fit properly)
6. The golf cart batteries don't use automotive type posts, so I had to cut off the ends of the battery cables, buy a heavy lug crimper (on ebay about $25), and crimp on some lugs to fit the new battery studs.

Notes: I didn't re-weld the battery hold-down rod, I just used lock nuts on the bottom outside. Also, I took advantage of having the batteries removed and scraped the corrosion out and reprimed and painted the inside of the battery box.
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Old 10-31-2015, 01:45 PM   #10
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Quote:
Originally Posted by WindyJim View Post
We did a similar project almost a year ago, only on a slightly smaller scale. Our 25' Airstream had two size 24 batteries and I switched them to two Trojan 6-volts. Increased capacity from approx. 80 AH per battery to approx 225 AH per battery (now 450 AH total instead of 160 AH total). What an incredible difference as we have solar and do mostly dry camping.
If your Trojan 6-volts are rated at 225 AH each, you now have 225 AH at 12V total, not 450. If you programmed your chargers based on the 450 AH number (and/or if you do discharge percentage calculations based on that number) you are overestimating by a factor of two.
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Old 10-31-2015, 01:51 PM   #11
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Quote:
Originally Posted by WindyJim View Post
We did a similar project almost a year ago, only on a slightly smaller scale. Our 25' Airstream had two size 24 batteries and I switched them to two Trojan 6-volts. Increased capacity from approx. 80 AH per battery to approx 225 AH per battery (now 450 AH total instead of 160 AH total). What an incredible difference as we have solar and do mostly dry camping.
Cable size will be determined in part by how large of an inverter you will be using. We do not use our inverter for the microwave or electric coffee pot, so extra large wiring not an issue. The wire we used earlier for the inverter wiring was MARINE wire.
BATTERY CONVERSION NOTES:
Converted from (2) 24-sized batteries to (2) 6-volt golf cart batteries ((2) Trojan T-105 Batteries 2*($125-$10pickup+$20core)+$21.60 tax).
Items:
1. Replace the 3/8" threaded rod (I think I went from an 8" to a 10", or a 10" to a 12", can't quite remember). Rod replacement is not easy because it is threaded through a nut which is welded on the outside bottom of the battery box, and then the rod is seal welded to the nut. You have to grind off about half of the nut in order to be able to unscrew the existing rod. (With the "undercoating" on the bottom of the battery box this was not evident, so thinking that you could unscrew the existing rod took a lot of time. I called the AS factory and the technicians went out on the floor to examine the bottom of the battery box, but still didn't know that the rod was welded. You cannot use a 3/8" rod coupler to extend the rod, as there is insufficient room for the larger gap required between batteries.
2. The size 24 batteries sit in a plastic shell at the bottom of the battery box. My local AS dealer just removes it and leaves it out, if they do the conversion. For me, I removed it, then cut out both ends of the plastic shell so that the golf batteries would sit on plastic in the bottom of the box.
3. The battery box has to be heightened. This was not a problem for my AS, but if someone has a forward storage outside door, they would have to have the box extended down, instead of up as I did it. I had some 1"X3" oak, so i just made a 2 1/2" extension on the top of the box, and moved the lid up, and it was fine. (Our local AS dealer can fabricate a 2" or 2-1/2" box extension, but opted to make my own.)
4. The two new 6-volt batteries have to be wired in series, instead of in parallel as the 12-volt batteries were.
5. I had to use a pneumatic "nibbling" tool to enlarge the propane tank cover cutout to fit the taller battery box (i.e. trim away 2 1/2" of aluminum to make the propane tank cover slip over the two propane tanks and fit properly)
6. The golf cart batteries don't use automotive type posts, so I had to cut off the ends of the battery cables, buy a heavy lug crimper (on ebay about $25), and crimp on some lugs to fit the new battery studs.

Notes: I didn't re-weld the battery hold-down rod, I just used lock nuts on the bottom outside. Also, I took advantage of having the batteries removed and scraped the corrosion out and reprimed and painted the inside of the battery box.
I'm interested in performing a similar upgrade and have been reviewing data sheets for flooded lead-acid as well as AGM batteries. I'm looking forward to following along with BoldAdventure when pictures and descriptions are posted. I will likely use AGM as I plan to install the batteries inside the trailer, under the couch. I'm familiar with putting two 6V batteries in series to obtain 12 V and hope to put two banks of series batteries in parallel to double the available capacity.

So... I'm not following your math. Trojan flooded lead-acid, T-105, 6V batteries are rated at 225 Ah (the 20 hour rate). Putting them in series doubles the voltage to 12V, but does not double the capacity. Putting batteries in parallel doubles the capacity. Please explain - perhaps I've overlooked something.
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Old 10-31-2015, 03:26 PM   #12
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You'll like it

We did this project a dozen yrs ago to store what our solar panels generate. The details today are a bit fuzzy but we used the existing compartments (after enlarging and taller doors) and built an inside chase for two batteries under the forward couch (sealed to inside/vented outside). This arrangement allowed short cables but made tongue weight a concern. As I recall, I calculated, then measured a new tongue weight w/in 60lbs. of max (and knew that I could further reduce by packing items aft of the axles). Battery maintenance is a bit of a pain, but doable… certainly worth the added performance if dry camping is a goal.
And yes, doubling 6 to get 12v does not double the amps. But two banks of 6v pairs that are paralleled does.
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Old 10-31-2015, 05:51 PM   #13
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Quote:
Originally Posted by WindyJim View Post
We did a similar project almost a year ago, only on a slightly smaller scale. Our 25' Airstream had two size 24 batteries and I switched them to two Trojan 6-volts. Increased capacity from approx. 80 AH per battery to approx 225 AH per battery (now 450 AH total instead of 160 AH total).
No you actually have 225 Ah

Quote:
Originally Posted by nvestysly View Post
So... I'm not following your math. Trojan flooded lead-acid, T-105, 6V batteries are rated at 225 Ah (the 20 hour rate). Putting them in series doubles the voltage to 12V, but does not double the capacity. Putting batteries in parallel doubles the capacity. Please explain - perhaps I've overlooked something.
You're on the right track, this is why I am wiring series parallel.

Series adds the voltage of the two batteries, but keeps the same amperage rating (also known as Amp Hours).



Parallel connections will increase your current rating, but the voltage will stay the same.



If you have two sets of batteries already connected in parallel, you can join them together to form a series.





You can learn more here: Trojan Battery Company
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Old 10-31-2015, 06:50 PM   #14
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True that two 6V batteries in series does not double the amp hours.

But, two 6V golf kart batteries in series have about 225 amp hours, which is significantly more than the 160 amp hours available from typical 12V batteries wired in parallel.

For this reason alone it is an upgrade worth considering. We did it, and are very glad to have the extra in reserve.
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