Do we need a multi-stage converter?

[dkottum]

Perhaps if the converter/batteries are in regular use powering the Airstream there is little chance of overcharging. If not it could be the cause of overcharging over long periods, or so it seems from our experience.

Could that be the reason Airstream is satisfied with factory single-stage chargers? Maybe I need to read my Owners Manual . . .

[lewster]

One of the factors directly relating to battery life is the number of charge cycles vs. depth of discharge. Lifeline has a chart in their tech manual that shows 1000 charge cycles for a 50% (12.2VDC) depth of discharge. That number increases dramatically to 5000 charge cycles when only using the battery minimally at 10% depth of discharge and conversely, drops significantly to 500 cycles at 80% depth of discharge.

This might be one of the reasons for your experiences with extended life of batteries using the OEM converter.

[Siegmann]

I think you guys are spot on (post #21,22). I would just reinforce that for those that still have the OEM converter, you do have to check the water level. Or they will not last a year. Exposed plates = death.

[dkottum]

Thanks guys, we understand our battery charging system a little better today. Some variables of use and effect we hadn't considered.

[PJohnson]

In my first post, I attempted to provide the information need to make an informed decision about replacing a single stage converter with a multi-stage converter. Since I have owned two Airstreams, one that I converted to a multi-stage converter and one that will not be converted.

My first Airstream was a 2010 Classic Limited 27’ Front Bedroom. Since the batteries were in individual compartments in the front of the trailer, not in the A-Frame compartment, it was quite inconvenient to hook up a battery charger to them.After 20,000 to 30,000 miles and 5 years, I decided to replace the single stage converter with a multi-stage converter. The reason I replaced the converter was to get a faster recharge. Since I did not have solar and I did not have access to shore power where the trailer was stored, I need to use a generator. Furthermore, the batteries need recharging far more than they needed to have thieir water levels checked (they were checked twice a year). I should point out that my Interstate batteries lasted 6 years before they had to be replaced.

My second Airstream is a 2016 Classic. Since the batteries are in the A-Frame compartment, I do not plan to change the converter. When I need to recharge the batteries, I will hook up the generator to the trailer, put the Battery Disconnect in the Store position and hook up a battery charger to the batteries. The only modification that I am considering for the converter is to add the Parallax TempAssure kit.The TempAssure module adjusts the converter voltage based on the battery temperature. Battery absorption and float charge voltages should be adjusted for temperature. If I was ordering a coach from Airstream, this is an option that I would have Airstream install since it requires having a sensor cable run from the converter to the battery. I am also thinking about solar.

Now, some thoughts about batteries. When I replaced the batteries in my 2010, I replaced them with AGM’s. When I traded my 2010 in on my 2016, I had the dealer switch the batteries so my new coach has the new AGM’s. I also have a diesel truck. Since diesel trucks have intake heaters (they no longer use glow plugs) and require a lot of power to turn over the engine while starting, there is a heavy draw on the two 12 volt truck batteries. This means that the alternator spend a lot of time putting out 14.4 volts. In addition, with the amount of time I spend towing my trailer, even if the voltage drops to 13.6 – 13.8 volts, there is the possibility of overcharging my AGM’s. While I has been stated that 13.6 volts will never charge a battery to 100%, which is not entirely true. Progressive Dynamics, the maker of the 4-stage converter, points out in their own literature that at 13.6 volts a full discharged 125 amp-hour battery will reach 100% charge in 78 hours.

[m.hony]

OK.
Let's complicate it a little further...
I just installed 2 new AGM batteries.
Will the OE Parallax converter/charger charge them?
Some say yes.
Some say no.
AGM batteries have great merit in my opinion due to no more corrosion evidently caused by the acid in flooded cell batteries and also seem to be able to be depleted and recharged a greater number of times.
If a get a new charger converter it will be the Progressive Dynamics PD9260 becuase I have a 50 amp trailer.
What say y'all?

[Michael_TW]

hello, thanks to everyone posting their information. there are some gaps though. My family are recent owners of a 25' FB Flying Cloud. From what I can tell, a multi-stage converter if installed directly as a replacement for the existing converter is useless and would have no impact on the battery performance. This would agree with some of the experienced posters here, and with the original poster. My basis is the discussion from the Parallax website. Most of the discussion would suggest that deep discharging the batteries is more likely the culprit than the converter. Also it seems like maybe just installing some cabling to quickly isolate the batteries with some alligator clips to hook up a proper 12V battery charger directly to a 120V generator might be a more cost effective solution, and would allow one to easily maintain the batteries when the trailer is on shore power or not in use. Any comments?

Follow-up Question: is everyone who is installing the multi-stage converters, installing battery isolation cabling/switches? are there separate outputs on the multi-stage converters that isolate the batteries from the regular DC supply (eg. two separate outputs?)

see below:
http://www.parallaxpower.com/faqs
Q: My friend has a "smart charge controller" that plugs into his converter system. Why hasn't Parallax offered a "smart" charger option for my unit?
A: The issue we have with "smart charger technology" (when used in an RV) lies more with the application of the technology than the technology itself. In a typical RV 12 volt electrical system, the converter/charger and the battery or battery bank is connected in parallel with the rest of the 12 volt distribution system. In "parallel" means where the charging source (converter/charger) positive and negative output is electrically connected to both the battery bank positive and negative, and the 12-volt distribution system positive and negative, at the same time. The voltage output of the converter "smart charger" is based on a "detected" battery voltage. The converter "smart charger" claims to "monitor" and respond to battery condition while connected to the entire 12 volt system. Unless the charging source (converter) has a separate or isolated charging output, we do not agree that a converter or charger can effectively differentiate requirements of the batteries from other 12 volt loads while simultaneously connected to the rest of the 12 volt distribution system in the RV.

Detected use or voltage change on the RV 12-volt load system (i.e. lights, pumps, etc. being turnedon) generally keeps these devices at a 13.6 -13.8 "float" voltage. This raises the question whether any real additional benefit is being provided to the battery bank unless the coach remains in a "non-use" storage condition. If a converter "smart charger" is only connected to the battery bank and can therefore monitor only battery voltage or current, and is not also connected "in parallel" with the 12 volt distribution system, we have no problem with the application of "smart charger technology".

[Michael_TW]

On another thread someone informed me that the store button is a full disconnect from 12V system, so alligator clips can be connected directly to battery from a dedicated charger (solar or generator). I reviewed the circuit schematic and the disconnect is via a relay on the positive side, maintaining a common ground.

someone suggested that a multi-stage converter will shut down based on a thermometer installed on the battery? Does a high temperature (from battery's increased resistance at full charge) result in the charger switching out of float mode to a lower voltage? Thanks!

[Michael_TW]

OK I found this to explain temperature compensation. Warm temperatures require lower voltages otherwise the batteries could boil even at 13.6 V. THis could explain why a single stage charger could boil batteries. But I don't see how a multi-stage converter without temperature compensation would be better than single stage.

http://www.bestconverter.com/Paralla...ure_c_104.html

[uncle_bob]

Hi

There have been a *lot* of threads on battery charging. I'm not real sure what this > 1 year old one has that's not in many of the others.

Some basics:

1) Battery disconnect switches vary a *lot* between AS models. What happens on this one is not what happens on another one. 2018's are different than 2017's. Generalizing about a single setting of the switch .... no way.

2) Battery voltages change with temperature. The whole "multi stage" thing moves voltages around by about a half volt. Change the battery temperature by 40 degrees and the correct voltages all move by a half volt or more. If you are running in a range of environments get a temperature compensated setup.

3) No matter how you do it, a varying load will confuse a basic multistage converter / charger. That's just physics. You could get fancier but the stuff we normally buy does not do so. The advantage of doing so is small in a typical "mostly in storage" scenario.

4) No matter how much you pamper them, all batteries wear out. You can kill them quickly, but you can't make them last forever and ever. Spending $10,000 to extend the life of $400 worth of batteries by a few months is not money well spent

5) Discharging lead acid's below the 50% capacity point wears them out more than the same number of discharges leaving more capacity to spare. Going further past 50% is worse . Taking them down to dead (like 11V at 70F) is not a good idea. Of course 11V at 130F is *very* different than 11V at 0F. If you are at 0F and at 11V, you are way past "dead".

6) Modern battery monitors try to track the battery by adding up all that goes into it and all that comes out of it. Unfortunately battery capacity changes with temperature. That can mess these calculations up. There is no perfect "no think" solution. You always will need to look at what's going on and understand how the battery bank works.

No, it's not easy and no, there is no silver bullet that fixes all the problems. There are some things that will help. None of them are 100% perfect.

Bob

[gandttimes]

Very interesting reading on why you need a multi stage charger? https://handybobsolar.wordpress.com/...ging-puzzle-2/.

[uncle_bob]

Hi

The gotcha is that the "awful" stock modern converters *are* multi stage. The real problem is not easily addressed without temperature sensing.

Bob

[Boogieshoes]

Have spent a LOT of time investigating the question of whether I need to change/upgrade to a multi stage converter. We have a 2016 Classic with solar/AGM and a PD 5355 converter. While there is a drop-in solution for the 30a, there is not one for 50a trailers. Not crazy about putting the Boondocker in given a separate mounting shelf appears to be needed. Also concerned about reports of excessive heat in the converter/elec panel compartment after changing to the Boondocker. Several posts in this thread suggest that I should just relax and go with what I have. Have not until now thought of putting the batteries on "store" mode when camping and hooked into shore power. Understand that solar will still charge the batteries in this mode. Planning to try that method next week at a rally. Appreciate so many of you sharing your knowledge; for a relative newbie (18 months) such as me, this is vital information.