When Towing The TM Which Regulator Controls Battery Charging?

[Philip]

Hello Folks,

I am considering upgrading my batteries on my 2008, 2720 TM since I plan to do a lot of dry camping. The problem is that any really good deep cycle battery, either Gell or AGM, requires a fairly precise charging procedure. The required procedure calls for a three step charging regimen(bulk, absorbtion and float) all with fairly precise voltage levels. Fortunately, my TM came with a three step charger which is used when plugged into 110V AC. This regulation may be adequate for an AGM battery but unfortunately will not meet a Gell batteries charging requirements. I have extensive experience with Gell batteries and am convinced they are more durable and less maintenance than AGM's but alas they need a special regulator. AGM's are still a vast improvement over other deep cycle batteries and they may be able to live with my TM regulator so I will have to go with them.

I know I am going on too long here but I need to know if while towing the TM does the TV alternator use it's internal regulator to charge the TM batteries or does the TV alternator output get regulated by the TM regulator?

If the TV alternator regulator controls charging I will not be able to use the AGM batteries since an automobile regulator is not acceptable. Yes I could install a proper external regulator on my TV but this is a costly project with many complications that I am not sure I want to get involved with. My TV is a 2005 Toyota 4Runner, V8 with a factory tow package(which comes with an upgraded alternator).

Any help would be appreciated,

Phil Friess

[ZekenSpider]

This is my experience with my new TM 3326. The TV is a 2004 Suburban with a 10 gauge wire to the TM tow receptacle. It has 30 Amp fuses at both the TV and TM battery buss end. As I get ready to tow, I set the refrigerator to 12 Volts DC (and refrig. fan on) with shore power still on. Then I connect the TV with engine running. The TV voltmeter sits at 14.7 volts. The TM battery voltage is 14.6. I disconnect shore power and see no change. The TV voltmeter stays at 14.7 volts for the length of the tow (so far, only 200 miles) and the TM battery remains at 14.6 volts whenever I stop, as long as the TV generator is running.

Unless you have a battery isolator (to isolate your TM from your TV) the two batteries (the TM and the TV) will be in parallel and will receive the same charging voltage from the TV generator. That voltage will be controlled by the TV generator regulator which is set to around 14.7 volts. The TV generator will jamb as much current into each battery as they each will accept based on their individual internal voltage levels and the voltage drop encountered in the wire length and size of each charging circuit. The maximum current into the TM battery will be limited by the TV or TM battery circuit fuse (or circuit breaker).

In practice, this means the TV generator(while running) will be a constant source of DC current at 14.7 volts into the TM DC buss. That buss will be providing continual current to your TM equipment (usually just the refrigerator) and to the TM battery up to the limit of the fuses. That will force the TM battery internal voltage to rise to 14.7 volts.

By the same analysis, when on shore power, the TM and TV battery will be charged by the TM inverter (if the TM and TV are still plugged into each other and the TV is not running). In addition, if you have a solar power system on the TM, the solar power regulator will charge the TM battery at a fixed 14.3 (adjustable) voltage.

The TM battery voltage always rises to the solar regulator set point. The only time I see the TM inverter 3 level control come into play is when parked in storage at night with no loads turned on.

I have wondered about using AGM batteries. Let me know if you think they will be durable. So far, in my application, I do not go very far into discharge cycle.

Jerry Miller

[Bill]

Jerry's synopsis is pretty good. Let me add a couple minor things. First, as Jerry said, when towing, the tow vehicle's regulator controls the voltage that is produced at the regulator. The voltage seen at the TM battery will always be lower, due to the voltage drop encountered in the wires running from the tow vehicle regulator to the TM battery and back. This can be several tenths of a volt, depending on the details of the wiring, and the amount of current being drawn through those wires. If the refrigerator is running on DC while you tow, it draws quite a bit of current, and so the charge voltage available to the TM battery will be considerably lower than the voltage seen at the tow vehicle regulator. In fact, for about 1 in 5 of us, the charge voltage drops so low with the refrigerator running that the TM battery actually begins to discharge while we drive. Four chances out of five say you won't be in that group, but nonetheless, the lowered voltage from the tow vehicle can't overcharge your TM battery.

As a second point, the 3-stage regimen for charging batteries (any battery, not just AGM or gel) usually takes a fairly long time to complete, even if full charge current is available from the source. And that's a big IF. Considering the reduced charge current available from the tow vehicle (even if the refrigerator is off), the whole cycle could take days to complete. In the few hours that you are driving, the cycle wouldn't complete, so you certainly don't have to worry about over-charging (which I gather is your concern).

Finally, as Jerry says, when you are plugged into shore power, the TM's charger will determine the charge voltage that is available to the TM battery. Many standalone chargers have a gel setting, but I'm not at all sure that the charger in a 2008 TM has one. Wish I had a manual - perhaps when you get your TM, you could forward the converter's model number to me and I'll look it up. Your choices would seem to be to a) charge the battery correctly at home, with the entire 3-stage regimen at the prescribed voltages, and let the battery take what it can get when you're camping with shore power, or b) replace the TM's charger with one specifically designed for your battery. In my opinion, this would be gross overkill, given that the TM's charger is already a 3-stage charger - but that's just my opinion.

Flooded (conventional) batteries, AGM, and gel batteries are all lead-acid batteries, and use the same chemistry. Both AGM and gel cells are sealed, so overcharging must be carefully controlled since any water lost to gasification cannot easily be replaced. But AGM batteries seem to be superior to gel cells, since AGMs use the same charging voltages as automotive batteries. They are considered a drop-in replacement for flooded batteries in deep-cycle applications. Gel cells, on the other hand, need a slightly lower charge voltage, as you mentioned.

To summarize, web sources say that you're OK for sure with an AGM. I think you are OK with a gel as well, because of the limited charge current available. When you have a choice, though, the sources I find say that an AGM is preferable because no special charge parameters are needed.

Further reading from a reputable battery supplier - http://www.windsun.com/Batteries/Battery_FAQ.htm

Bill

I have extensive experience with Gell batteries and am convinced they are more durable and less maintenance than AGM's but alas they need a special regulator.


On a side note to this post, I do not understand the above statement. As I have never had a Gel battery I cannot speak to that. I CAN attest to the reliability of a AGM battery, also its ability to be maintenance free (at least the one I have, a Lifeline AGM). I have had this battery for over 3 years, and I have done nothing, absolutely nothing to it. During the winter it was stored in the garage, where the temperature regularly got into the teens and twenties. Each spring when I took it out and put it in the TM I didn't even have to recharge it. I couldn't be happier with this battery, especially having to deal with water, charging etc. with the original battery. A whole lot more expensive that a regular deep cycle battery, but to ME it is worth every penny.

Mike Anderson

I am rather perplexed about the advantages of gel or agm over flooded batteries.

I have a pair of Interstate group 24 RV/marine batteries

We have had hookups 4 times since 2005.

We camp about 6 times a year, for not more than a week.

I have added water to the batteries once.

My batteries have been in use since March 2005, a little over 4 years.

Of all of my concerns about preventative maintenance around the house, trucks, cars, motorcycles, ATVs, pool, etc. the TM batteries are at the bottom of the list.

I guess if I was full timing then I would have a different experience. But for weekend camping flooded cells seem to be problem and maintenance free.

Am I just lucky?

Well Wayne....I guess I was unlucky. On my old Aliner with a Interstate battery, I was constantly charging it and adding water. Now mind you I have a good battery charger A Xantrex 10 (or some such number), which does the 3 stages of charging you and many others recommend. I got sick and tired of every time I wanted to go anywhere I had to mess with that battery. Not the least of which having to keep distilled water available. It is possible it was defective (although it did work when I had it charged), but that experience soured me, such that I was willing to pay a LOT more for the Lifeline battery I eventually bought. Obviously, you (and many others) have had excellent luck with regular RV batteries and that is great. For me I will not go back.

Mike

Just a guess, your Aliner may not have had a 3 stage converter.

My TM has a 3 stage charger, but it is not the top of the line either.

I have never seen any evidence that the water has boiled in my batteries. It sounds like you had an over charging problem.

[Philip]

Originally Posted by PopBeavers

I am rather perplexed about the advantages of gel or agm over flooded batteries.

I have a pair of Interstate group 24 RV/marine batteries

We have had hookups 4 times since 2005.

We camp about 6 times a year, for not more than a week.

I have added water to the batteries once.

My batteries have been in use since March 2005, a little over 4 years.

Of all of my concerns about preventative maintenance around the house, trucks, cars, motorcycles, ATVs, pool, etc. the TM batteries are at the bottom of the list.

I guess if I was full timing then I would have a different experience. But for weekend camping flooded cells seem to be problem and maintenance free.

Am I just lucky?

Hello Wayne,

I would guess that you are not just luckey. I think that the duty cycle your batteries see is not beyond the capability of your batteries. I don't know if you have a battery monitor to tell you the AH you use in a day but I would guess that you use less than 50% of your battery capacity on a regular basis before you are able to recharge. If you are able to do this, with even less expensive batteries, you will get fairly good life out of them. Also only using them for 6 weeks out of the year helps a lot.

I would say you selected the most cost effective battery for your needs.

Should you change your usage significantly in the future(increase your daily electrical load for some reason or start to dry camp for much longer periods during a year) you may want to keep an eye on your batteries.

Have a wonderful remainder of the season,

Phil Friess

[Philip]

Originally Posted by ragmopp

I have extensive experience with Gell batteries and am convinced they are more durable and less maintenance than AGM's but alas they need a special regulator.


On a side note to this post, I do not understand the above statement. As I have never had a Gel battery I cannot speak to that. I CAN attest to the reliability of a AGM battery, also its ability to be maintenance free (at least the one I have, a Lifeline AGM). I have had this battery for over 3 years, and I have done nothing, absolutely nothing to it. During the winter it was stored in the garage, where the temperature regularly got into the teens and twenties. Each spring when I took it out and put it in the TM I didn't even have to recharge it. I couldn't be happier with this battery, especially having to deal with water, charging etc. with the original battery. A whole lot more expensive that a regular deep cycle battery, but to ME it is worth every penny.

Mike Anderson

Hello Mike,

I agree with your experience. The AGM battery is a vast improvement in durability and maintenance reduction over any wet cell battery. From my experience, the Gell is slightly better since it never needs any conditioning for sulphate removal and maintains its capacity during a long life without any attention - except proper regulation.

Prior to getting into this RV life I lived for ten years aboard my sailboat traveling the total Carabbean, Bahamas and Bermuda. I completely revamped the electrical platform to allow myself to stay at anchor virtually all the time with no need for marinas or shore power. This required a robust charging, regulation and battery system since all the amenities on board were 12 volt(refrigerator, freezer, large R/O watermaker, lights, pumps etc.) I consumed approx. 110 AH a day. The three 8D gell house batteries(660 AH) lasted over 12 years(used them two years prior to full time live aboard) with absolutely no maintanance. They probably could have lasted longer but I decided to replace them prior to traveling in some very remote areas where it would be inpossible to get batteries should I need them.

I knew fellow cruisers who used AGM batteries and got very good service out of them but not the kind of service I realized out of gell batteries. The capacity of the AGM tends to go down faster than Gells as they age. Reconditioning helps but I expect that this is hard on them as it has to cause a loss of some water. Any time I encountered a cruiser who had trouble with their gell batteries, after investigation I found out that they did not have the proper regulation for gell batteries which caused the short life.

This is my experience but keep in mind that the AGM is quite close in performance to a Gell( IMHO) and far superior to any wet cell.

Wet cells cannot perform as well as Gells or AGM's since they must rely upon thich plates to provide the strength to stay together when discharged. This thick plate is impossible to charge/discharge swiftly as it takes time for a charge to penitrate into a thick plate. Gell's and AGM's can have thin plates since the gelled electrolite in a Gell holds the plates together when discharged and the glass mat in a AGM serves the same purpose. There are many other details but this is the main one.

I know I have been too long winded yet again, but the bottom line is that you have an excellent battery in the AGM thus you have realized the benifits of this battery.

I may also be getting an AGM in the future.

Take care and happy trails,

Phil Friess

[Bill]

Philip –

The discussion seems to have gotten off track here. My comments addressed solely the matter of AGM vs. flooded batteries. Now gel batteries are back in the mix.

Gels require a special charging regimen, as you noted in your original post. As you also noted, if you treat a gel cell properly, it is a very good battery. There is no argument here.

AGM batteries do not require a special charging regimen, which was your original question and the subject of my follow-up. I think you have agreed with this conclusion, though I’m not sure. Again, do you have information to the contrary?

As to whether or not AGMs are “worth it”, that is a separate question. And as to whether or not you can believe the manufacturers’ claims of extended life, that is also a separate question. You asked about charging regimens.

Like you, I tend to discount manufacturers’ claims for their own products. I try to find independent sources of info, from sources that are knowledgeable but don’t have a direct financial stake in selling you the product. On the question of batteries, there are many. I tend to like Northern Arizona Wind and Sun. They are a nationally-known company that deals with solar power systems, largely for homes, rather than RVs or boats. Their financial interest is in selling you a solar power system that you will like over the long haul. They don’t want to deal with unhappy customers, so they concentrate on good reliable equipment. They used to sell both AGM and gel batteries (as well as flooded). They dropped gel batteries, and they explain why in the tech library portion of their web site. They were just having too many calls from unhappy customers, because of the charging problems. If they sell you a gel cell and a special charger, all is well and they have a happy customer. But if they sell you a gel cell and you add your own charger, and the gel cell dies, guess who gets the nasty phone call? They got tired of that.

I included a link to Northern Arizona Wind and Sun in my post above. I think their explanation of the differences between the three types of batteries is comprehensive and quite understandable. They cover physical construction, charging requirments (and why gels are different), recombination of hydrogen and oxygen, lifetime, cost, and other interesting topics. You might read it.

So again, on the question of whether AGMs require a special charging regimen, the answer is “No”. Are they worth the extra cost? That is a separate question and different people will have different answers.

Bill