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Old 02-12-2014, 07:05 PM   #1
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Sizing converter & 12v vs 6v coach batteries

Hello y'all I was hoping to get some opinions about my coach. This in the converter I just installed. It's 60 amps which replaced the old single stage battery boiler that was on the coach and wanted to know the maximum amount of batteries I could charge with it. I wanted to know if I could charge 4 coach batteries with it or if I should just get the taller Trojan 6v batteries. It currently has interstate 12v for the chasis and interstate 6v for the coach and both sets are 7 years old and don't hold charges well. Literally KAPUTTTTT! Input from personal experience on the 6v in series or 12v in parallel would be great
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Old 02-12-2014, 10:11 PM   #2
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I've been checking on batteries myself. Have always heard the 6 volts, what my rv has now, have a longer run time. But what I've actually seen by the stickers on the batteries is the 12v have a longer run time but provide lower amps. So now I'm up in the air which to get. We fire up the Honda 2k inverter generator when we go to bed to run the furnace and let it run until its out of gas and then hope the batteries will last the rest of the night. But if its really cold and the furnace is running a lot they rarely make it till morning. We have dual batteries for the coach.
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Old 02-12-2014, 11:20 PM   #3
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I have a 30 footer and am using just regular pick up truck size batteries.
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Old 02-13-2014, 02:35 AM   #4
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You'll need two different types of battery. A pair of 12V starting batteries paralleled up to start your main engine and generator, and a bank of 4 (or 6) 6V deep cycle batteries wired in series/parallel to provide 12V support for the house circuits. Use golf cart batteries (Trojans) for the house application. They are true deep cycles, designed to be drained down and then recharged over and over again. Do not be tempted to use marine deep cycle batteries. These are not true deep cycles, and will not serve you well.
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Old 02-13-2014, 04:56 AM   #5
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Quote:
Originally Posted by Jmoney7269 View Post
Hello y'all I was hoping to get some opinions about my coach. This in the converter I just installed. It's 60 amps which replaced the old single stage battery boiler that was on the coach and wanted to know the maximum amount of batteries I could charge with it. I wanted to know if I could charge 4 coach batteries with it or if I should just get the taller Trojan 6v batteries. It currently has interstate 12v for the chasis and interstate 6v for the coach and both sets are 7 years old and don't hold charges well.
The PD9200 series was a good choice - it will serve you well. It has a maximum rated output of 60amps. I can tell you that by checking actual/real charge rates on them over the years you will likely only average 1/2 the rated maximum charge output.

So to answer your question, if you are charging a bank of batteries rated at total of 450ah (4-6v GC2 batteries in a combination series/parallel setup which is the most common setup) your PD9260 is most likely going to charge at a maximum rate of around 30 amp on average. So if your batteries are say 50% discharged which would be around 12.4 volts you need to put approximately 1/2 their rated output back into them, which is 225ah. At an average 30amp charge that would take around 6-8 hours. There are several factors which will skew that total time such as the ambient temperature but this is all a good educated "guess". If your coach charges both house and chassis at the same time then you need to add your chassis battery approximated ah (even though starting batteries don't have an AH rating there is a formula to figure one) which will increase the charge times too.

If you ask the battery manufacturers, they recommend chargers being sized anywhere from 10%-25% of the rated ah capacity of the battery banks you're charging. I heard one thing from one, something different from another :-)
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Input from personal experience on the 6v in series or 12v in parallel would be great
If you are already setup for 4-6v (combination series/parallel) for your house then I think the Trojan T-105s or the GC2 6V batteries will serve you well depending upon how much AH you require. I'm sure others can chime in their experiences boondocking/dry camping. I personally have 4-GC2 batteries for my house setup and a PD-9245 converter which, for my normal and usual usage, work just fine - but I don't boondock.. ever.
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Old 02-13-2014, 06:01 AM   #6
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Quote:
Originally Posted by 89sandman View Post
I've been checking on batteries myself. Have always heard the 6 volts, what my rv has now, have a longer run time. But what I've actually seen by the stickers on the batteries is the 12v have a longer run time but provide lower amps. So now I'm up in the air which to get. We fire up the Honda 2k inverter generator when we go to bed to run the furnace and let it run until its out of gas and then hope the batteries will last the rest of the night. But if its really cold and the furnace is running a lot they rarely make it till morning. We have dual batteries for the coach.
Run time is dependent solely on the amp-hour capacity of the battery bank and nothing else. It doesn't matter whether you use 6 or 12-volt batteries, although frequently the 6-volt units are better built for deep-cycle service so they are a popular choice.

BTW if you can't run the furnace even a single night then it's likely there is something else wrong, i.e. your current batteries are in poor condition, they weren't fully charged, etc.
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Old 02-13-2014, 06:24 AM   #7
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Quote:
Originally Posted by 89sandman View Post
I've been checking on batteries myself. Have always heard the 6 volts, what my rv has now, have a longer run time. But what I've actually seen by the stickers on the batteries is the 12v have a longer run time but provide lower amps. So now I'm up in the air which to get. We fire up the Honda 2k inverter generator when we go to bed to run the furnace and let it run until its out of gas and then hope the batteries will last the rest of the night. But if its really cold and the furnace is running a lot they rarely make it till morning. We have dual batteries for the coach.
A 12V battery has 6 cells which are half the capacity but deliver 12VDC because they are in series. A 6VDC battery has only three cells in series that deliver 6VDC, but are twice as large with twice the capacity...so two 6V batteries in series gives you 12VDC with twice the capacity. (Two 12VDC batteries in parallel will do the SAME thing.)
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Old 02-13-2014, 06:24 AM   #8
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An old timer told once told me, "pick up a 12v battery then pick up two 6v batteries. Feel the weight differences....which one do you think will last twice as long?" I found out that old guy was right They also cost twice as much for the same reason, which makes sense.
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Old 02-13-2014, 06:32 AM   #9
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6V golf cart batterys
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Old 02-13-2014, 07:01 AM   #10
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Currently I only have 2 coach batteries which are the interstate 6 volt. I wanted to know if my charger/converter would have any problems charging 4 6v batteries in the series/parallel combination.
It will have no problems charging the batteries back up, whether it's 2 or 4 or even 8. The time to complete a full charge simply increases with the number of amp hours you're charging using the sample formula in my previous post. More amp hours = more time to recharge using the same PD9260 charger. If a 450 amp hour battery bank (4-6v batteries in a combination series/parallel wiring setup to achieve 12vdc) is completely discharged, at a 30amp charge rate it will take approx 15 hrs to fully restore them.. IF the 30amp charge rate is maintained constantly.

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So from what I have read that on a bank of 4 6v batteries for the coach, the charger would only be charging at like 30 amps?
Your PD9260 will average only around a 30amp charge rate regardless of the number of batteries it's charging. You can verify this yourself by using a clamp-on ammeter while the unit is in bulk charge mode.
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Old 02-13-2014, 07:48 AM   #11
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Your PD9260 will average only around a 30amp charge rate regardless of the number of batteries it's charging. You can verify this yourself by using a clamp-on ammeter while the unit is in bulk charge mode.
yes. My understanding was that the 60amp rating was for the total amount of DC power it provides to the entire coach. The battery charger portion would provide the 30amps or so to the batteries.
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Old 02-13-2014, 09:58 AM   #12
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The unit will provide 60 amps, it is not split by function (battery charging vs. supply to coach.) Whatever power not being used by the coach should be available to charge the batteries. The reason for less than that amount (i.e. perhaps 30 amps out of 60) is that 30 amps is all the current that can flow at a given charge voltage and state of the battery (internal resistance, etc.)
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Old 02-13-2014, 04:01 PM   #13
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How to pick a converter. Method one, two and three

First you need to know two things, One is the size of the wire since you do not want a fire. (Too small a wire, not a good thing). Do not exceed the capacity of the wire.. Or, upgrade the wire (your choice) that is method 2 by the way.

now, Method 1

You need to know the C/20 amp hour rating of your batteries, (Amp hours at the 20 hour rate). The following are close

Group 24 75 amp hours
Group 27 95
Group 29 100-105
Group 31, 130
GC-2 pairs (Two six volt in series) 230

Add up your total c-20 amp hours

For flooded wet cells and Generic AGM (NOT LIFELINE) Xantrex suggests 30% C-20 as the peak recharge rate.. So for each 100 am hours (per the above chart) you want 30 amps.

LIFELINE suggests 25% (they used to say 30 but I rechecked last week) as the MINIMUM initial charge for their AGM. and you wont find a converter that is able to hit their max recommended rating so I won't worry about that, if you want to know, find their pages.

TROJAN, for their Flooded wet cells, Recommends a max charge rate of 10% of the C-20 (That's method 3)

10% will generally give longer battery life but what you save on fuel for your generator will more than make up for the shortened life with the 30% rate.

The body builder on my motorhome (Damon) used 30% when they picked the converter (progressive Dynamics 9180 with wizard charging a pair of GC-2 plus the chassis (Group 78) and a bit to the house for good measure)
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