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Old 03-10-2018, 10:07 PM   #1
WanderOne
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Existing "New" 12V. Add 2 6v or 2 12V to get 3

Hi,

I have a new Cougar 25RES 5w and want to add solar for boondocking this summer.

I have a new Interstate 12V 27 series that came with it.

I am thinking about a few options.

1) Add 2 Trojan 6V batts and keep on separate system. Then use Trojans 6v as primary and have switch for existing 12V for backup. Not sure about charging config with two different banks.

2) Add 2 more matching 12V Interstates Batts to the existing and have 3 12v batts system.

3) Just dump the 12V. and Use 2 6V Trojans for system (as I have read that 2 6V can be as stronger than 2 12V? But would they be better than 3 12V?

At the end of the day I am wanting to have 300W Solar system on roof, and Pure Sine Inverter maybe 2000Watts.

What would experienced Solar Boondockers opt for?
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Old 03-11-2018, 02:12 AM   #2
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I’m not a boondocking expert, but I’ll try to shed some light.

It’s all about amp hours with the batteries.

What are you trying to power with the inverter?
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Old 03-11-2018, 06:07 AM   #3
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Old 03-11-2018, 07:21 AM   #4
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It sounds like you are not planning on a generator in this setup. I'm absolutely no expert on on this but this sounds like a lot at potential draws on the system.

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Old 03-11-2018, 07:38 AM   #5
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Originally Posted by WanderOne View Post
Hi,

I have a new Cougar 25RES 5w and want to add solar for boondocking this summer.

I have a new Interstate 12V 27 series that came with it.

I am thinking about a few options.

1) Add 2 Trojan 6V batts and keep on separate system. Then use Trojans 6v as primary and have switch for existing 12V for backup. Not sure about charging config with two different banks.

2) Add 2 more matching 12V Interstates Batts to the existing and have 3 12v batts system.

3) Just dump the 12V. and Use 2 6V Trojans for system (as I have read that 2 6V can be as stronger than 2 12V? But would they be better than 3 12V?

At the end of the day I am wanting to have 300W Solar system on roof, and Pure Sine Inverter maybe 2000Watts.

What would experienced Solar Boondockers opt for?
The difference with 2 6 v in series vs 2 12 v in parallel are 12v will charge equally to the limit of the battery with the least capacity, likewise the available amps, is. One with 50 amp hours and one with 100 you have 50 amp hours available. 12 v batteries even deep cycle will not tolerate a total discharge without damage and will only survive a limited amount of discharging below 50% before the battery capacity recharge is reduced. 6 v batteries, especially those designed for golf carts are not as susceptible to these issues. You would need a battery isolator to charge both 6v and 12 v batteries from the same source. Hope this makes sense.
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Old 03-11-2018, 06:09 PM   #6
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This is the way I understand it but I am by no means an expert. So someone please correct me if I am wrong.

It is all about the amp hours. A typical 27 series 12 volt deep cycle battery is 90 amps. When you connect them in paralllel the voltage stays the same and you add up the amperage. So 3 of them connected in parallel would be 12 volts and 270 amps.

Most 6 volt batteries are between 180 and 225 amps. When connected in series the amperage stays the same but you add up the voltage. So 2, 6 volts hooked up in series will become 12 volts but the amperage stays the same. So 2, 6 volt batteries with 225 amps would be 12 volts at 225 amps.

That means 3, 27 series, 12 volt batteries at 90 amps each would have more amps than 2, 6 volt batteries at 225 amps each.

This is in perfect conditions which we pretty much never have but at least it will give you an idea. Then you need to find out the amp draw on the appliances you want to run. This will determine how long the batteries will power said appliances.

If you start with 270 amps and have a 2.7 amp draw you will be good for 100 hours. If you have a 27 amp draw you will only last 10 hours. If you have a 50 amp draw your batteries will only last about 5 hours.

Then look at the output of the solar panels you install. If the appliances draw less than the solar output you will be good, at least while the sun is shining. If they draw more than the solar panels can produce you will drain the batteries. Of course solar output is dependent on sunshine. So it will vary from day to day, angle, shade from trees, cloud cover etc. Then if you plan on watching your tv in the evening after the sun goes down you will be relying completely on the batteries.
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Old 03-11-2018, 06:13 PM   #7
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Use this (or google to find another) to calculate your power needs.

http://www.rvsolarelectric.com/index...directory_id=3

As for batteries, for the most efficient system they should be the same, even manufactured at the same time.

I have two 6v T-105's and 200w panel which will allow me to draw 100ah/day though with only 200w solar it would basically take one and a half to two sunny days to recover from that here in NH. You seem like a heavy current user so you may be looking at more batteries and more solar.
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Old 03-11-2018, 06:25 PM   #8
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Without going to a solar calculator to give an accurate answer, off the top of my head your 300w solar should charge a pair of T-105's discharged to 50% (around 110ah) in 6 hours at maximum panel output (21ah). That is at ideal conditions, something that one doesn't always have.

You should always have a backup generator when relying only on solar.
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Old 03-11-2018, 07:59 PM   #9
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The difference with 2 6 v in series vs 2 12 v in parallel are 12v will charge equally to the limit of the battery with the least capacity, likewise the available amps, is. One with 50 amp hours and one with 100 you have 50 amp hours available. 12 v batteries even deep cycle will not tolerate a total discharge without damage and will only survive a limited amount of discharging below 50% before the battery capacity recharge is reduced. 6 v batteries, especially those designed for golf carts are not as susceptible to these issues. You would need a battery isolator to charge both 6v and 12 v batteries from the same source. Hope this makes sense.
I like the idea of using a battery isolator and having the 12V as a backup. I will put a separate outlet to near TV and entertain area that will come from an Inverter from the pair of 6 volts, that will be for TV, laptop and phone charger. And the House 12V will run LED lights and water pump, heater fan.

Question, Will a battery isolator work with a single 12v on one side and 2 6 volts on another (2 banks - my thought)?

Also yes, I will also carry a Champion 3500w Inverter/Generator Dual Fuel for Air conditioner needs or other.
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Old 03-11-2018, 08:27 PM   #10
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This is the way I understand it but I am by no means an expert. So someone please correct me if I am wrong.

It is all about the amp hours. A typical 27 series 12 volt deep cycle battery is 90 amps. When you connect them in series the voltage stays the same and you add up the amperage. So 3 of them connected in series would be 12 volts and 270 amps.

Most 6 volt batteries are between 180 and 225 amps. When connected in parallel the amperage stays the same but you add up the voltage. So 2, 6 volts hooked up in parallel will become 12 volts but the amperage stays the same. So 2, 6 volt batteries with 225 amps would be 12 volts at 225 amps...
You connect 12 volt batteries in parallel, to sum the available current, if you put 3 of them in series, you would sum the voltage and end up with 36 volts.

The 6 volt batteries would need to be connected in series, to get to 12 volts.

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Old 03-12-2018, 05:12 AM   #11
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You connect 12 volt batteries in parallel, to sum the available current, if you put 3 of them in series, you would sum the voltage and end up with 36 volts.

The 6 volt batteries would need to be connected in series, to get to 12 volts.

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Woops.. you are right.. i had it backwards. I went back and fixed it. Thanks

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Old 03-12-2018, 06:00 AM   #12
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I like the idea of using a battery isolator and having the 12V as a backup. I will put a separate outlet to near TV and entertain area that will come from an Inverter from the pair of 6 volts, that will be for TV, laptop and phone charger. And the House 12V will run LED lights and water pump, heater fan.

Question, Will a battery isolator work with a single 12v on one side and 2 6 volts on another (2 banks - my thought)?

Also yes, I will also carry a Champion 3500w Inverter/Generator Dual Fuel for Air conditioner needs or other.
To answer the isolator question yes because the out put of the 2 6 volt are 12 volts so in effect if you take the outputs it's the same as 2 12 volt batteries. To do it automatically search for "battery isolator, one alternator two batteries". Be prepared as this will cost $150+.The more economical solution is a manual disconnect...search "battery disconnect, two batteries". It will have a selector with 1,2. both. Both connects both batteries and you would need to use that to charge the batteries.
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Old 03-12-2018, 02:30 PM   #13
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To answer the isolator question yes because the out put of the 2 6 volt are 12 volts so in effect if you take the outputs it's the same as 2 12 volt batteries. To do it automatically search for "battery isolator, one alternator two batteries". Be prepared as this will cost $150+.The more economical solution is a manual disconnect...search "battery disconnect, two batteries". It will have a selector with 1,2. both. Both connects both batteries and you would need to use that to charge the batteries.
I thought that because we have two different systems (banks - 1 12v and 1 Duel 6s) that you cant just send straight charge to both as it will have trouble knowing what is charged to what point, and other things? That is why I thought I need an Isolator. Or if you are just saying set selector to 1 or the other, then that makes sense. But that means remember to watch battery levels for both and then manually switching daily.
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Old 03-12-2018, 03:54 PM   #14
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I thought that because we have two different systems (banks - 1 12v and 1 Duel 6s) that you cant just send straight charge to both as it will have trouble knowing what is charged to what point, and other things? That is why I thought I need an Isolator. Or if you are just saying set selector to 1 or the other, then that makes sense. But that means remember to watch battery levels for both and then manually switching daily.
Yes, manually switching them for both discharge and charge....probably a horrible solution.

Once you determine what your daily draw will be I would invest in the right amount of watts for the roof and T-105 batteries and forget the dual banks unless you do something automatically. I know you can get solar charge controllers for dual banks but why go through the added expense of that and an isolator when you can just sell your group 27 and get the required number of 6v batteries. I sold a pair of well cared for Grp 24's for 60 bucks...we were both happy with that.
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Old 03-12-2018, 06:29 PM   #15
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Yes, manually switching them for both discharge and charge....probably a horrible solution.

Once you determine what your daily draw will be I would invest in the right amount of watts for the roof and T-105 batteries and forget the dual banks unless you do something automatically. I know you can get solar charge controllers for dual banks but why go through the added expense of that and an isolator when you can just sell your group 27 and get the required number of 6v batteries. I sold a pair of well cared for Grp 24's for 60 bucks...we were both happy with that.
You know, that is sounding like a great idea. The question is not really how to do it,... more like what would experienced boondockers do or suggest.

Thanks
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Old 03-12-2018, 06:33 PM   #16
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Do you have any idea of your required power consumption?
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Old 03-12-2018, 07:02 PM   #17
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Do you have any idea of your required power consumption?
Not actual no.

Estimate these things

Refer
Coffee maker in AM
We have a 44in LCD TV - four hours night maybe - 120 watts
Furion DV3300 DVD movie included in TV use
Antena Booster - Winegard Roadstar
2 laptops - maybe 1 hour each
2 phone chargers
Microwave maybe one thing a day 2 mins 1350watts
LED house lighting ?
Frurion Ent system Stereo 3 hours a day
Furnace Fan - 50 watts when running
Various detectors
Water Pump

We will have a Generator For AC or Charge Batteries when needed. We are in Southern California, so it does get warm in the Western US in the summer.
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Old 03-13-2018, 03:22 AM   #18
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Since you'll likely be running the AC and thus the generator in the warm months, then relegate the coffee maker and microwave to the generator and your system can be reasonably sized but you really shouldn't pick your solar components without first giving your power consumption a lot of thought. Heck, one might even say that you don't need solar if you're planning on running the AC long enough to also charge the batteries.
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