Batteries: parallel versus series for battery strings and other battery stuff

[belfert]

I would like to replace my batteries with AGM batteries so I can move them inside.  I have eight golf cart batteries now in a bad location and don't want to sacrifice bay space for flooded batteries.

I had a long talk with Tom Duffy at The Solar Biz about batteries as they have really good prices.  He said to never connect batteries in parallel as the battery or battery string with the least resistance will get charged and the other battery or string(s) won't get a proper charge.  He said to always connect batteries in series.

Has anyone else heard about only connecting batteries in series?  Series strings of batteries really limits how many amp hours you can get, especially at 12 volt.

The Solar Biz sells some high capacity 2 volt and 6 volt batteries, but the cost is $2000 to $3000 for a 24 volt bank and the 2 volt batteries would weigh 1200 lbs!  Tom recommended a pretty beefy battery bank based on what I told him about useage.


I'm thinking I might just get two 8D AGM batteries and just run the generator more often.  I don't use the bus often enough to justify $2000 to $3000 for batteries.  I'm also thinking about a third 8D AGM battery just for 12 volt loads and get a 3 stage charger for it.  This would reduce the load on the 24 volt bank somewhat.

I've seen UPS batteries at 2 volt that are available from 100 amps to over 1000 amps, but I can't find anyone with pricing online.  These may be cheaper, but I don't know.  There are three or four battery places locally I need to call on Monday.  (No, not Batteries Plus)

[DrivingMissLazy]

I would like to replace my batteries with AGM batteries so I can move them inside.  I have eight golf cart batteries now in a bad location and don't want to sacrifice bay space for flooded batteries.

I had a long talk with Tom Duffy at The Solar Biz about batteries as they have really good prices.  He said to never connect batteries in parallel as the battery or battery string with the least resistance will get charged and the other battery or string(s) won't get a proper charge.  He said to always connect batteries in series.

Has anyone else heard about only connecting batteries in series?  Series strings of batteries really limits how many amp hours you can get, especially at 12 volt.

The Solar Biz sells some high capacity 2 volt and 6 volt batteries, but the cost is $2000 to $3000 for a 24 volt bank and the 2 volt batteries would weigh 1200 lbs!  Tom recommended a pretty beefy battery bank based on what I told him about useage.


I'm thinking I might just get two 8D AGM batteries and just run the generator more often.  I don't use the bus often enough to justify $2000 to $3000 for batteries.  I'm also thinking about a third 8D AGM battery just for 12 volt loads and get a 3 stage charger for it.  This would reduce the load on the 24 volt bank somewhat.

I've seen UPS batteries at 2 volt that are available from 100 amps to over 1000 amps, but I can't find anyone with pricing online.  These may be cheaper, but I don't know.  There are three or four battery places locally I need to call on Monday.  (No, not Batteries Plus)

Absolutely pure BS in order to try and sell the higher priced 2 volt cells. It is not unusual to connect up to four strings in parallel with up to 50 12 volt batteries in each string. And these were guaranteed for up to 10 years use.

Richard

[H3Jim]

I think he may have a point that the different strings can absorb different amounts of charge, but its not enough of an issue to only buy 2 volt cells.   I think it may be more important to use solar charging so you can always keep the batteries completely topped off.  I found I never could get a full charge using my generator.  I think because I would not let it run the extra 2 or 3 hours for that last 5% of charge.

I have 600 watts of solar charge, but you don't need nearly that much if all you're going to do is keep yoru bats topped off when everything is off.  I repeat, I think solar charging (constant, although just as good to keep it plugged in all the time too) is more important for battery life than almost anything else you can do.

I have 6 AGM batteries, 4-D, 12 volts.  3 sets of 2 in series.  24 volt house system.  200 amp hours per battery (at 12 volts) 600 amp hours (at 24 volts) for the three, 2 battery sets.  Two of my batteries are above the rear wheels, on their sides.  The other 4 are where the old bus toilet tank used to be, next to the engine.  4- ought cables connecting all.  Batteries weigh 128 lbs each.  Cost about $1800 for the set.  I have been Very happy with the set up, its about 3 years old.  I may have more batterey than I need, I rarely go below 75% charge, but I leave the refer running 24 /7 using only solar to charge the bats, so they go down some every night.

Recommended to buy all batteries together at the same time, minimizing different charge rates and absorption.

[gumpy]

With the generator you have, I personally think it'd be a waste of time and money to switch to AGM or anything other than golf cart batteries. I can get you trojan T105 220 ah batteries for probably around $80, though I haven't priced them for a couple years. 8 of those would run your coach for 2 or 3 days, and then run the gen to charge them back up.

email or call if you'd like me to check on the exact price.

craig

[belfert]

With the generator you have, I personally think it'd be a waste of time and money to switch to AGM or anything other than golf cart batteries. I can get you trojan T105 220 ah batteries for probably around $80, though I haven't priced them for a couple years. 8 of those would run your coach for 2 or 3 days, and then run the gen to charge them back up.

I have 8 golf cart batteries right now bought from Sam's club with all the same date.  They won't last a day before they need charging.  My frig supposedly takes 1.2 amps and is manual defrost.  We also used 24 volt flourescents, 3 or 4 laptops, and a 12 volt cooler on the last trip.

I made a mistake with the placement of the batteries.  They are in a tray next to the engine where the A/C compressor and the Webasto used to be.  The batteries get in the way of servicing the air compressor and other stuff on that side of the engine.  I also noticed they get snow blown in on top of them as the access door is vented.

The batteries really need to be moved and I don't really have a good location to place them other than next to the generator if I built a set of shelves.  I think going to AGM and putting the batteries underneath a bunk inside would be better.

[Nick Badame Refrig/ACC]

Hi Brian,

Have you checked the water level in your batts lately? Or have you equalized the bank?

Not doing this can result in shortened battery life and capacity.

Nick-

[D+C4106]

Nick,  Would you or anyone else elaborate on the equalization process.  Will the batteries need to be new? Our battery bank does not seem to last as long as it is implied that it should either.   Thanks for enlightening us on this,  Denis

[Nick Badame Refrig/ACC]

Hi Dennis,

Q: What is charge equalization?
A: Conventionally, "Charge Equalization" is a technique used to reduce imbalances in series connected battery strings. The goal is to equalize the capacities of individual cells/modules within a given string.

Q: How is charge equalization accomplished?
A: Conventional "Charge Equalization" is accomplished by applying a low chnarging current for an extended period of time at elevated voltages (C/20 for 24 hours, where C is the 5- or 10-hour discharge rate for a given battery).

Q: How frequently should a battery be equalized?
A: Most manufacturers recommend equalization to be performed at some regular periods. In many cyclic applications such as electric vehicles, weekly equalization is recommended. The key to periodic equalization schedules is to prevent cell-to-cell imbalances from progressing to a point where it corrupts the performance of the overall string.


Hope this helps
Nick-

[Sean]

Nick,  Would you or anyone else elaborate on the equalization process. ...

All flooded batteries need to be equalized periodically.  Equalization is essentially a controlled over-voltage charge that helps mix the electrolyte and knock some of the sulfation off the plates.

Rather than elaborate further, here are two good sites that describe the process:

http://www.thesolar.biz/Battery_charging_article.htm
http://www.amplepower.com/primer/equal/index.html

Those were, in fact, the first two results when I typed "battery equalization" into Google.

I recommend equalization at least monthly.  Remember to remove Hydro-Caps, if used.  Your charger should have a setting for "equalization" -- if not, you will need to dial in the proper settings manually.  Get the equalization parameters (voltage and time) from the manufacturer of your batteries -- every make and model is a bit different.

-Sean
http://ourodyssey.blogspot.com

[TomC]

I too have two Lifeline 8D AGM deep cycles.  I run the reefer (5 amps running) lights and light inverter stuff like TV and stereo for 24 hours.  When dry camping, just run the generator in the morning (to heat the water and the coffee), and then once again at night to refresh the batteries.  Totals maybe about 3 hours running a day.  If you're not using the bus much (I use mine about 5 times a year) then just running the gen (especially if you have a good reliable Diesel gen set) is a lot cheaper than buying and supporting a huge battery bank.  One way or another, without solar panels, you'll still have to run the generator about the same amount of time-whether it be 2 or 3 hours a day, or 12-15 hours worth every fourth day to charge up multiple batteries.  As I see it, having a big bank of batteries just cuts down on the frequency that you need to run the generator, not the total amount of hours.  Now if you have the additional solar panels, that would be completely different.  But once again, if you're only using the bus a few times a year, solar panels are REALLY expensive for the amount of amps you get out of them.  If you're full timing, then you could justify them.  Personally-just run the generator-that's what it is there for and most Diesel gen sets will go 20,000 hours before overhaul with just regularly changing the oil and filters.  Considering that I only have 600 hours on my gen over the last 7 years, I should be able to pass my generator down to my family for generations to come.  Good Luck, TomC

[Lin]

Just to note that obvious.  Even if joining batteries in parallel is somehow inferior, there is no really choice in the matter.  How you wire your batteries is determined by what you need to do.  I can't see using some elaborate, prohibitive scheme to meet a theoretic goal when the simplest, cost effective method works.

[Sean]

...  As I see it, having a big bank of batteries just cuts down on the frequency that you need to run the generator, not the total amount of hours.

While that might seem to make sense on the surface, it does not work that way.  In fact, if that were true, then we could reduce the size of the batteries down until they were infinitesimally small without adding to the overall generator run time, but I am sure everyone here realizes that if batteries were that small, we'd have to run the generator continuously.

The reason has to do with generator capacity and charger rates.  Let me propose an example:

You have a (fairly typical) 6KW generator and a (fairly typical) charger than can charge at around 130 amps (at 12 volts, which I will use to keep this simple).  If you have only, say, 100 amp-hours of battery capacity, then 50 amp-hours of that is "usable" in a typical cycle.  Let's further suppose that you use 50 amp-hours each day.

In this scenario, after you have used your 50 amp-hours, you start the generator (which will be once per day, since we are using 50 amp-hours each day).  Assuming flooded batteries, they will absorb charge at about 20% of their capacity on average (faster in the earlier stages, when they are more fully depleted, and slowing down considerably as they get more and more charged).  With our 100 amp-hour bank, that's 20 amp-hours per hour, or a total of 2.5 hours of run time to re-charge the 50 amp-hours.  That's every day.  In actual practice, if you only run the genny for the 2.5 hours daily, the batteries will never "soak" and they will lose a bit more capacity every day.

Now let's keep everything the same, except increase the size of the battery bank to 500 amp-hours, or five times as large.

At 50 amp-hours per day, you will be able to go 5 days before taking this bank down to the 50% mark (250 amp-hours).  Now when you run your generator, assuming you are not pulling more than about 35 amps from it for loads other than the charger, you can charge at almost the full rate of the charger, putting 100 amp-hours per hour back into the batteries.  That's five hours of generator run time to fully charge the bank, or an average of 1 hour a day.  (Although, again, at this rate they will never soak.)

In this admittedly simple example, we've cut the overall generator run time down by a whopping 60% by increasing our bank capacity by (an also whopping) 500%.

The numbers get even better if you use AGM batteries instead of flooded, as AGM can accept a higher rate of charge.  Things get even more complicated when you add in the complexity of recharging from the (generally cheaper to run) engine alternator, and/or solar panels.

The point here is that the "optimal" size for your battery bank, if you do a lot of boondocking and your goal is to minimize generator run time, is a function of your charger and generator capacities.  Generally speaking, the more battery capacity you have, the less overall generator run time will be needed, up until you have so many batteries that you have exceeded the charger's capacity to charge them at their maximum rate.

As a matter of practical experience, we have an all-electric coach, and, in temperate climates (no air conditioning, and minimal or no heating), we use about 150 amp-hours per day from our ~900 amp-hour 24-volt battery bank.  We can usually go four days without starting the generator.  When the generator starts, it will run for about four hours.  I'd like to say that it works out to an average of one hour run time per day, and it does for about a week or so.  But if the batteries never get a chance to soak, as I wrote above, they lose a bit more capacity (or recharge a bit less, if you prefer to think of it that way) every cycle, and we get less and less time between generator runs, dropping to roughly two days between runs, or two hours average per day for long-term (weeks on end) boondocking.

If we drive for four hours or so every couple of days, we never have to run the generator, a fact which would not be true if we had only a pair of 8D's instead of the eight we have now.

Bottom line is that you need to figure out how you intend to use the coach, then size all the components accordingly.

-Sean
http://ourodyssey.blogspot.com

[D+C4106]

Nick, Sean, Tom and Lin,    Thanks so much for the info,  now I see where I need to make some changes.   Thanks,  Denis

[Sojourner]

Amen Sean!

About charge equalization:
THIS ONLY PERTAINS TO NON-SEALED BATTERY.

Because you add or take away water from each cell somewhat more or less from next cell. By adding or take away water will variation of 0.05 specific gravity from each other until it is equalized.

So there is no need to equalization a sealed battery. A waste of time and money. Other word if it ever un-equalized, it is already a bad battery.

It is important that all parallel and/or series batteries are builds with same brand, date if possible and bash....or you can get un-equalized batteries between the 2. And you will more likely get less performance for your money.

About parallel or series batteries:
Each 12v battery contains 6 cells in series of 2v each. By adding another sister battery either parallel to double the current capacity is like 1 bigger battery......or series to double the voltage output is like 1 longer battery.

Again... It is important that all parallel and/or series batteries are builds with same brand, date and bash....or you will more likely get less performance for your money.

Other word a 12v battery contains 6 cells of same date, brand and bash. So by adding another 12v battery to it...just be sure it has the same brand, date if possible and bash of the other battery.

I hope anyone that was not clear before, now have it corrected.

This is not my rule...it the law of physics.

FWIW

Sojourn for Christ, Jerry

[niles500]

Sean points out one of the best arguments for solar (H3JIm has a great system too) - It takes forever to top off the AGM's and a 10 to 15kw genset is a waste to operate in order to accompolish that - a properly sized solar array will allow you to shut down the genset, finish that last 5 or 10%, and float the batts without wasting fuel and genset cycles - If you are boondocking - when you get up in the AM you can start the genset, bulk your batts, load the genset up by turning on WH, taking your shower and letting the WH replenish for use during the balance of the day, cooking and using as much current as you can - when your done shut down the genset and let the solar do the rest (by this time the sun will be high enough for your array to do its work during peak hours) - HTH