!2 volt to 6 volt?

[Bruce H]

I recently converted my two Interstate Deep Cycle 12 volt batteries to two Interstate Deep Cycle 6 volt batteries. Everyone says this is the way to to go! I was a bit disappointed on our first trip to a national park (no hookups). My wife and I both noticed the lights were not as bright as when we had the the 12 volt batteries (batteries were fully charged). Do the two 6 volt batteries have as much power as the two 12 volts batteries? Also I didn't see that the 6 volts lasted any longer than my 12 volt set up. Was I supposed to use four 6 volt batteries? Would not have the room for 4 anyway. Your thoughts on this will be appreciated.

[Midniteoyl]

It all depends... what were the 12v's and what did you replace them with?

Did you hook the 6v's in Series?

[JMonroe]

Do you have the six volts hooked up in series, or parrallel? If hooked up correctly your lights should be as bright as ever. The 6 volts will typically have a higher amp hour capacity than the 12 volts, and usually will last for more deep cycles (full discharge / recharge) than a 12 volt.

I'd guess there's a problem in how they were hooked up. If you simply attached the battery cables the same way the 12 volts were hooked up, you've cut the power to your lights by 50%.

[Gary RVRoamer]

The voltage should be exactly the same if you hooked the 6v in series, so the light brightness should be identical. Whether or not the 6v's last longer depends on what size 12v's you had previously. A pair of 6v's generally has about 220-225 amp-hours (AH) of capacity. That's more than 2 x size 24 12v's (170 AH) or 2 x size 27 12v's (about 200 AH), but the same as 2 x size 29 or size 30 (about 220 AH).

[BryanL]

re: "Everyone says this is the way to to go!" - it is rather sad you got caught by this scam.

The amount of energy you have in a battery bank depends mostly upon its weight, not voltage. Plan on about 10 to 15 usable watt hours per pound of battery.

How long your batteries will last depends mostly upon how you use and maintain them, not brand, voltage, or marketing hype terms that have no measurable definition.

Whenever you change battery configuration, you do need to pay careful attention to wiring to make sure that you get the proper voltage output from your battery bank and that you balance the currents.

Don't confuse measures and units. Batteries store energy. That is most conveniently measured in watt-hours. Power, measured by watts, is mostly an issue only in choosing wire and fuse sizes and calculating total energy needs over time.

Batteries often show energy as amps times hours. This is OK when the voltage is always the same. It is usually less confusing to multiply a battery amp-hour rating times its voltage to get watt hours so voltage assumptions are not at play.

Keep in mind that battery energy specifications are for about 60 watt power draws. If your needs are different, you'll get a battery energy available that is different from the rating.

The amount of energy in a typical RV battery is rather small, just a couple of percent of typical household daily usage. That means that trying to add batteries to solve energy deficiencies in RV use can be disappointing unless you have already made the RV energy lifestyle a habit.

Common wisdom about batteries as seen in many of these discussions is often out of date or not backed by any objective or rational measure. Take care and look for objective measures that the manufacturers and retailers will stand behind. These are things like you see on spec sheets or warranties or cost.

[Bruce H]

Thanks for your responses. I will try to answer your inquiries. The batteries are now in a series ( Battery one positive to negative on battery 2 and then all the cables that were positive on the 12v battery are on battery 2 and all the cables that were on 12v negative are on Battery 1) I had a picture to follow. The 12v batteries were Interstate Deep cell group 27 and I think were 190 AH. The 6v batteries are Interstate Workaholic Extreme Heavy Duty 122 min. @ 75 amp 232 AH. They feel twice as heavy as the 12 volt batteries. The salesman said there were equivalent to golf cart batteries or better and are new from Interstate. However now that I look at them I do not see anywhere that says deep cell and maybe HD is the same. When I measure the volts from the negative on battery 1 and the positive on battery 2, I get 12.8 volts. What do ya think?

[Midniteoyl]

So the GC2-XHD's. Those are the U2200 replacements and are a great battery. If hooked up and charged correctly, they should have given you a longer run time. Although, thats only another 2-4 hours worth. Longer if you deep cycle them lower than the old ones.How long and to what voltage did you charge them too before using them?

Interstate Batteries

[RJay]

Hi Bruce H,

You connected the batteries properly. Are you Workaholic batteries U2200 by chance??

[Ray,IN]

A battery is only as good as its connections and cables. Are the battery cables new, or cleaned and inspected for corrosion before re-using? Battery cables do wear out-so to speak. Clamps become varnished, and must be cleaned away with a wire brush or it creates high resistance, even insulates the battery from the cable wire-albeit infrequently. If the cable wire is corroded inside the clamp, the only solution is to replace the entire cable assembly.

[Bruce H]

The batteries are the GC2-HDX-UTL that Midniteoyl spoke of. I assume they are the the replacement for the U2200. I did wire brush the cables and they look pretty good. I'm not sure about the proper charging. I charge both batteries at once with a 12 volt 10 amp charger each morning for about 2 hours or so after using all night running the propane heater.

[Ed-Sommers]

Quote:

Originally Posted by Bruce H The batteries are the GC2-HDX-UTL that Midniteoyl spoke of. I assume they are the the replacement for the U2200. I did wire brush the cables and they look pretty good. I'm not sure about the proper charging. I charge both batteries at once with a 12 volt 10 amp charger each morning for about 2 hours or so after using all night running the propane heater.

You are vastly undercharging those batteries. You need a good three stage charger that can get up to the recommended charge voltage, and then hold it there for two to four hours.

I recommend you go to interstate battery web site to get their info for those batteries, and I believe you will find that a charge voltage of 14.8 to 15 is needed.

Ed

[Midniteoyl]

Quote:

Originally Posted by Ed-Sommers You are vastly undercharging those batteries. You need a good three stage charger that can get up to the recommended charge voltage, and then hold it there for two to four hours. I recommend you go to interstate battery web site to get their info for those batteries, and I believe you will find that a charge voltage of 14.8 to 15 is needed. Ed

Agreed.. and would be the reason you are getting the amount of run time on these as the others - you are putting the same amount in.

[wa8yxm]

Quote:

Originally Posted by Bruce H The 12v batteries were Interstate Deep cell group 27 and I think were 190 AH.

They might be 190 AH TOGETHER but odds are they were closer to 100 AH each. Your current 2-piece 12 volt battery is 220 amp hours. Not a lot of difference. (both within 10% of 200)
Opening a PDF file on my computer (Thank you Interstate)
The chart does not give the 20 hour amp hour rating for the G-27 Marine/Deep cycle but it does give the number of hours at 5 amps... 20.4 That's close enough that I can use it.. 102 amp hours. each, 204 for the total at the 20.4 hour rate.. So your 190 is very likely "Combined amp hours" for the two batteries.

NOTE: that the RESERVE CAPACITY is 180 minutes at 25 amp which is likely what confused you.

(Why I keep that PDF on the HD)

What is the difference in the batteries?

Well there are 3 classes of batteries
Starting batteries are designed to deliver a big rush of current very fast.. They can dump 10-20% of their charge in as little as a mintue. But ... Do not "Deep Discharge" them at least not very often because they do not like that and the first time you kill 'em dead.. You may well need to replace them.

Marine/Deep cycle are a bit (SMALL BIT) more forging of a deep discharge.. But only a little bit.. They are primarlly starting batteries but.. Well.. not quite the same peak amps, and they don't mind a slight discharge..

DEEP CYCLE.. can often deliver the amps needed to start an engine because.. Well.. on my Workhorse the Deep cycle pair is 220 amp horus.. the primary starting battery is like 80, so 10 percent is 8 amp hours for the primary.. That's less than 3.5% of the bigger battery's charge so the peak amps is not a problem for them on occasion when I have to use the E-Start button.

But they also do not mind a 50% discharge.

And that is the big differnece.

So, for 100 pounds of battery, you get the same number of amp hours no matter WHAT the type and configuration.

DEEP CYCLE tend to give longer service life in the HOUSE BATTERY compartment.... and because of the tremendous number of those batteries made for the golf car industry.. They cost less per unit to make than the assorted 12 volt formats.

And when you wire two sixes in series as you do in an RV.. They become one BIG 12 volt battery (roughly an 8-D)

Think of them that way.. Always treat them that way. NOT as 2 six volt (Save when lugging them by hand) but as a single 12 volt battery.

[BryanL]

re: "Well there are 3 classes of batteries" -- this is very misleading marketing hype. The reasons for why it is marketing hype include the fact that there is no hard measure to delineate one class from another and also that differences in the batteries you usually find for RV and automotive use are matters of degree and not kind.

for example: "But they also do not mind a 50% discharge." -- the battery life versus depth of discharge is similar for all the batteries considered here. None "mind" being discharged to halfway nor even to the usual deep cycle mark of 80%. What happens is that deeper discharges as a routine thing shorten battery life - and this is true for most batteries. A cost analysis of battery cost efficiency (i.e. see smartgauge.com) indicates that a halfway discharge cycle is about optimum.

Note that even starting batteries will handle sufficient deep discharges under lab conditions that make typical RV use a non issue in this regard. (the range is from about 200 to 800 deep cycle discharges). There are other factors at play as well that make this 'deep cycle' marketing hype of minor significance in RV considerations. (reference to a full analysis available on request)

What this class of battery division does is to provide an indication of the market that a manufacturer is trying to sell the battery to. That helps them determine warranties, for example.

Also - be very careful talking amp hours. Those apply only for a given voltage. That is why it is always better to compare in watt hours so you don't get caught making mistakes comparing batteries of different voltages. Also keep in mind that battery energy capacity is highly dependent upon the power draw. Most ratings (the 20 hour one) are for about a 60 watt power draw for the typical 60 to 100 pound battery usually used in RV's.

Battery measures should also be considered as rather imprecise. Factors such as temperature, cycle to cycle variation, age, and use profile can each make a 10% to 20% variation in available capacity.