Six-volt Batteries and Battery Charger

[seahunter]

Hello,

I have read that a good way to charge your batteries is to use an automotive-type battery charger (like with the onboard generator) as it is much quicker than going through the trailer's charging system. If I have two six volt batteries, can I do this with a 12-volt battery charger? If so, which battery do you hook it up to?

Thanks much!

Greg

[Gkerlin]

Hey Greg,

If your batteries are hooked up in series to produce 12V (I assume they are) then yes you can as long as you put the pos and neg leads across the WHOLE bank - not a single battery.

That said however - I don't see how a battery charger would be a better choice than the onboard factory converter - even with its faults - unless you have a really good multi stage charger. Two 6v batteries are not that large a bank to replenish.

I'd also be careful about using both charging sources at once (the onboard converter and external charger) as you need to be cognizant of how many amps you are trying to put in all at once. AGM batteries can accept higher charge rates but the lead acid are more finicky.

A rule of thumb would be about 15%-25% charge rate for your bank capacity.

So if you had a 200ah bank - then 30-50 amp charge rate is optimum.

Faster is not always better.

Hope this helps.

[RichR]

I camp out of reach of commercial power,that means I use a generator to charge my batteries.Charging from the converter would never charge the batteries enough unless you ran the generator all the time.I have used a battery charger for over ten years to do the charging and works well with minimal generator run time.

[Gkerlin]

quote:Originally posted by RichR

I camp out of reach of commercial power,that means I use a generator to charge my batteries.Charging from the converter would never charge the batteries enough unless you ran the generator all the time.I have used a battery charger for over ten years to do the charging and works well with minimal generator run time.

Just curious... what size battery bank do you have? What size/make charger? is it a multi-statge charger? How far down do your run the batteries, and how long does it take to charge them back up? Do you run the converter and the charger at the same time? How long are you out off the grid in a year doing it this way?

More info would be helpful. Thanks

[seahunter]

quote:Originally posted by Gkerlin

Hey Greg,

If your batteries are hooked up in series to produce 12V (I assume they are) then yes you can as long as you put the pos and neg leads across the WHOLE bank - not a single battery.

That said however - I don't see how a battery charger would be a better choice than the onboard factory converter - even with its faults - unless you have a really good multi stage charger. Two 6v batteries are not that large a bank to replenish.

I'd also be careful about using both charging sources at once (the onboard converter and external charger) as you need to be cognizant of how many amps you are trying to put in all at once. AGM batteries can accept higher charge rates but the lead acid are more finicky.

A rule of thumb would be about 15%-25% charge rate for your bank capacity.

So if you had a 200ah bank - then 30-50 amp charge rate is optimum.

Faster is not always better.

Hope this helps.

Thanks Greg for the reply. When you say "as long as you put the pos and neg leads across the WHOLE bank - not a single battery" - Does this mean the positive on the battery going to the trailer and the "free" negative that's not wired to the other battery?

So as not to have two charging sources - the generator and the battery charger - should I hit the battery disconnect before charging with the genny or would that help or even work?

[seahunter]

quote:Originally posted by RichR

I camp out of reach of commercial power,that means I use a generator to charge my batteries.Charging from the converter would never charge the batteries enough unless you ran the generator all the time.I have used a battery charger for over ten years to do the charging and works well with minimal generator run time.

Thanks for the reply Rich. I am curious as to how long it takes to charge with the generator as well.

[Irlpguy]

Your two 6V batteries will be connected with the neg of one battery (#1) going to ground on the frame of the Rv, the pos side of that same battery (#1) will be connected to the neg side of the other battery (#2) and finally the Pos side of the second (#2) battery will be going to your circuit breaker. As long as you hook the Neg of battery #1 to the neg on the charger and the Pos of the battery #2 to the pos on the charger you will be ok and will be seeing 12V.

I would use the battery disconnect if you are going to charge from your generator or a charger just to be sure you do not damage the circuitry of the RV converter.

I would never charge a battery at more than 12 - 15 amps, rapid charging will damage the batteries very quickly and can boil out the water quickly with repeated quick charges. Make sure you check the water level. The best little tool you can have in your tool box for batteries is a hydrometer, they are cheap and are the best indicator of the condition of a battery by checking the specific gravity of the cells.

If you are not connected to shore power and want to charge your batteries "only", then do so with the generator or a battery charger connected to the generator and don't even connect to the RV, although I would still use the battery disconnect to isolate the batteries from the converter.

I sometimes have charged my batteries with a Honda 500Watt generator that I used to carry with me, it will not run much in the RV but is great for charging the batteries, it puts out about 12 amps and depending on the discharge condition of the batteries it may take a couple of hours to bring them back up.

[seahunter]

Ed, thanks very much for the great explanations. I really appreciate it.

I forgot to mention the generator is an onboard Onan tied directly into the trailer if that makes a diffence between a stand alone generator. So then if I run the generator with a battery charger plugged into it and connected to the batteries - if I use the battery disconnect it will still charge the batteries if I understand correctly and not go to the inverter? Does that make sense??

[Gkerlin]

Greg,

Your assumption is correct... one lead on the negative going to the chassis, and the other on the positive going to the trailer.

For what it's worth - just because someone does something "successfully" for 10 years does not mean its the smart thing to do. I asked a number of questions to try an glean some insight into what the other poster was doing. There are many variables to consider - none of which were specified in that post.

I personally do not see the reason for using a charger instead of a multi stage converter/charger. Speed is not necessarily a good thing. Your RV comes with a decent (not the best - but decent) charger. Using an off the shelf charger - unless its a quality multi stage unit will not be as good for your battery bank as the factory unit. If it is a quality unit - then it will just charge the batteries slower anyway.

Its true that it will take a fair amount of time to recharge a discharged bank with your converter - but there is a reason for that. Trying to jam to many amps into your bank in a short period of time will not fully recharge batteries, even though you might think so. Batteries can only accept a charge so fast. Trying to jam it in faster will boil out the water, and damage them over time. If you have only one battery - no big deal. When you ruin it you can replace it. If you have a larger expensive bank like I do - I wont subject them to an overcharge by simply trying to recharge them in a short time no matter what.

There are a ton of variables that determine the optimum rate for a given situation... temperature, capacity, battery type - but the bottom line is - lead acid batteries - 15-25% recharge rate. Period. Try to do it faster - your going to damage batteries over the longer term.

Oh and by the way - FWIW - we spend almost all of our time - many months per year - off grid as well.

Instead of spending money on an external battery charger I'd invest in another battery and let the converter do its job. JMHO

[seahunter]

Greg,

Thanks so much for taking the time to explain that so well. I think I get it now about a battery charger frying the batteries unless it is a really good one that does it properly. I think I will just go with the trailer's own charging system.

So I guess the next question is, is it even practical to charge the batteries with the generator since it would have to run so long?

[Gkerlin]

Greg,

What do you have for batteries?

and yes - if you are boondocking you can (and must) charge from the generator. The problem is simply that you get a good portion of your capacity (say 80%) back relatively shorter time - but the remainder comes back slowly so you never really get a full charge unless you leave it running for a long time.

You learn to live with the batteries not being 100% when boon docking.

Then when you get somewhere on-grid, you can let the batteries come back up to 100%.

The problem with batteries not getting up to 100% over time is sulfation. (google "battery equalization" and you'll learn about what I'm referring to)

When batteries spend a good deal of time at less than full charge you need to do an equalization to keep them in top shape and long life. that is one of the places where the factory charger is not the best as it can't do an equalization charge. That doesn't mean you have to go out and junk your charger however... Just another thing to learn so that if/when the time comes that you decide to put in an inverter/charger - you understand the concepts and then specify a charger that can equalize.

But yes - yes- yes.... you can charge your batteries with your generator.

We are sitting in Quartizite right now and all around me I hear generators running charging their batteries. Fortunately I have solar so we are sitting here not needing to run ours. :-)

[seahunter]

Hey Greg,

Thanks again for all the help! I have a LOT to learn. When we ordered the Montana, we did as much research as possible, but sort of just got a few items that were recommended - such as the dual six-volts and the generator - and are still just learning how they all work, and work together. I don't remember the brand and rating on the six-volts, I'll have to check that.

Quartzite sounds like a great time! I hit your link and saw some of the pictures - weather looks great. We hope to do that in the future. I think we'll be okay on power consumption on the dry camping, but still haven't managed to do so well on the water consumption when we have been without hook-ups. I like my showers, and am doing better, but we'll probably need a back-up water source .

Enjoy Ft. Montana!

[Irlpguy]

I did not understand your generator was onboard seahunter. Since it is onboard and not a portable, the advise and explanations given you by Gkerlin are excellent. He obviously knows a thing or two about batteries and living off grid.
You should be on your way to some understanding of that part of your Montana now, I hope any other challenges are no more difficult to resolve.

[RichR]

To answer questions-I run dual 6 volt batteries,since it is very cold when camping(during hunting season)and being there for 10-14 days I try to charge every day.To avoid noise I run the generator during the day when we are gone.My charger has 2,4,6 amp charge rates and will shut off when charged.I paid about 50 dollars for the charger at Walmart.I would say that the generator runs about 8 hours,however some days I don't have to charge.Keeping the charge level up helps keep run time to a minimum.My batteries are 9-10 years old and are still doing great.I like to charge at 2 amps,seems to hold charge in batteries longer for some reason.

[Carl n Susan]

quote:Originally posted by Gkerlin



When batteries spend a good deal of time at less than full charge you need to do an equalization to keep them in top shape and long life. that is one of the places where the factory charger is not the best as it can't do an equalization charge.

If you have a recent Montana the standard Intellipower converter includes their "Charge Wizard" technology which includes (among other things) a desulphation capability. Here is a quote from their website:





The Charge Wizard is our patented microprocessor-controlled circuit built into all our PD9200 Series converters. The Charge Wizard constantly monitors the RV battery voltage and then selects one of three charging voltages and one of four operating modes to properly re-charge or maintain the RV battery. The addition of the Charge Wizard makes all our 9200 Series converters an intelligent battery charger. It will safely and rapidly recharge a discharged battery by automatically selecting the Boost Mode (14.4V) to rapidly re-charge the battery to 90% of full charge. Once the battery reaches 90%, the Charge Wizard automatically selects the Normal Mode (13.6V) to safely complete the charge. The Storage Mode (13.2V) is automatically selected after 30 hours of no significant usage of the 12-volt RV electrical systems. The lower charging voltage in the Storage Mode of of operation reduces battery gassing and water usage, while maintaining the charge. Every 21 hours when the system is operating in the Storage Mode, the Charge Wizard will automatically switch to the Desulfation Mode of operation. The Desulfation Mode increases the output voltage up to 14.4 volts for 15 minutes. This increased voltage mixes up the battery electrolyte to help prevent battery stratification and the resulting problems of battery sulfation.
Reference - http://www.progressivedyn.com/prod_d...ge_wizard.html

[Gkerlin]

I know that the Progressive Dynamics literature says that but it's a carefully worded marketing piece by the marketing department. If you read it closely it does not say it does an equalization.. It merely "helps prevent" sulfation and that is really just when sitting on a long term float situation. The intermittent bump to 14.4v pretty much helps prevent stratification of the battery acid but doesn't remove sulfates from the plates as the voltage is just not high enough to do that.

Each time you discharge a battery it forms sulfates. Without equalization it will slowly and continually lose some capacity. That's just physics... (actually Chemistry) A progressive dynamics charger helps to slow that sulfating some - but doesn't stop it.

that why i say its better than most battery chargers but its not really a top notch unit.

A proper charger must have temperature compensation as the differences between cold and warm temperature charging voltage requirements are fairly significant. For a Trojan Flooded battery for instance you would add .168v for every 10 degrees below 80 degrees so a battery that should charge at 14.7v at 80 degrees should charge at 15.54v at 30 degrees. The progressive charger doesn't have that ability. At each phase (Bulk, Absorption, Float) It charges at a set voltage regardless of temp. At 80 degrees F 15.54v would be an equitation charge. If you did that for an extended period of time your batteries would be gassing and need water. At 30 F that is just an normal charge voltage and gassing would be minimal. Your equalization charge at 30 degrees would be over 16v.

Also - if a battery is sulfated the 14.4v charge wont do anything. An equalization charge needs to be in (depending on battery make etc) 15.5 volt range - again temperature dependent.

Theres a ton of info out there on Temperature compensation and equalization of lead acid batteries and how it improves the performance and extends the life of batteries.

In many cases people will think their batteries are shot and lost their capacity, and all they need is an equalization.

Here is just one link to Trojans website. If you read down you'll see where they talk about temperature compensation.

Both my Magnum Inverter/Charger and my Tristar MPPT Solar Controller have temperature compensation. When its cold out - the voltages going into the batteries are higher. When its warmer - the voltages are lower.

[seahunter]

quote:Originally posted by RichR

To answer questions-I run dual 6 volt batteries,since it is very cold when camping(during hunting season)and being there for 10-14 days I try to charge every day.To avoid noise I run the generator during the day when we are gone.My charger has 2,4,6 amp charge rates and will shut off when charged.I paid about 50 dollars for the charger at Walmart.I would say that the generator runs about 8 hours,however some days I don't have to charge.Keeping the charge level up helps keep run time to a minimum.My batteries are 9-10 years old and are still doing great.I like to charge at 2 amps,seems to hold charge in batteries longer for some reason.

Sounds like you have a good system worked out Rich. Nine to ten years on the batteries would be excellent. Unfortunately with propane, I won't be able to get that kind of run time from what I'm hearing. I did get the 40# cylinders, but I know the Onan burns it up fast.

[seahunter]

Thanks Carl and Greg for that added information. I now know just how much I DON'T know about batteries and charging.

Knowing that at least the onboard charger is fairly intelligent, I will feel better just using that and not going with the stand-alone charger. By the way, I have a 2013 Montana (built May/June 2012)- do you know which specific converter model they came with?

Thanks again for the info and links!

[Gkerlin]

The model number should be on a sticker inside the converter panel door but Id guess (never assume with Keystone) its the same as my Monty which is a 2012. My converter is the PD 4590.