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Old 03-25-2016, 12:52 PM   #1
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Do we need a multi-stage converter?

There are many people suggesting that we all need multi-stage converters. In fact, there are only two good cases for multi-stage converters: leaving your trailer plugged in all the time and batteries in need of a rapid recharge. Furthermore, both of these cases have good alternatives. Before discussing the alternatives, let us look at how one of the most widely recommended multi-stage converters works.

The Progressive Dynamics converters with the built in Charge Wizard such as the PD4655 are advertised as a 4-stage converter. Actually, it is a 3-stage converter that operates in 4 distinct modes. When the battery is less than 90% charged, the converter puts out 14.4 volts (Boost mode).Once the battery reaches 90% charged, the converter puts out 13.6 volts (Normal mode). After 30 hours of electrical system non-use, the converter output drops to 13.2 volts (Storage mode). Finally, every 21 hours in Storage mode, the converter increases the output to 14.4 volts for 15 minutes (this is called the Equalization mode).

So how does this relate to how we actually use our trailers? First, unless we are storing the trailer, plugged in with the battery switch in the USE position, the converter will never drop to the 13.2 volt level. Therefore, once the battery is more than 90% charged, the converter output will be similar to the output of a single-stage converter. On the other hand, if our battery needs to be recharged, the Boost mode (14.4 volts) will certainly recharge the battery much quicker that the single stage converter. This may be an advantage for those of us that are boon docking with a generator. A better option for a rapid recharge is a dedicated battery charger. Modern battery chargers have a charge profile that is quite different that just boosting the output voltage to 14.4 volts. Furthermore, most of these chargers have dedicated modes for standard flooded cell, AGM and gel batteries. A discussion about battery charge profiles is for another time. I should mention, a battery charger might also be useful for our tow vehicle.

What has not been mentioned is this question of determining how the battery charge is determined. We use the voltage! Now we have a new problem. Charge state as a function of voltage is only accurate if the battery has been rested for more than 4 hours. If we have a load on the battery such as using the furnace, than the battery voltage drops and the converter assumes that the battery may need charging.

So how then, do we keep from cooking our batteries? We use the Battery Disconnect switch.In the STORE mode, the coach will still get power from the converter while the battery is isolated from the converter. If we need to top off the batteries, we put the Battery Disconnect switch in the USE position and if we need a rapid recharge, we use a dedicated battery charger.

Now for the real question. How do we keep from cooking our batteries when we are driving across the country and our tow vehicle is putting out 14.4 volts constantly? Note: the Battery Disconnect switch does not isolate the battery from the tow vehicle.
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Old 03-25-2016, 01:04 PM   #2
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It was as easier and quicker to put in a new state of the art converter than read your post.
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Old 03-25-2016, 01:07 PM   #3
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I vote multistage with trickle charge….BUT

I was sitting around the campfire, with a mechanic and a rocket scientist, both with 20 some odd years RV experience. We were discussing batts and chargers.

They basically told me to have fun….USE your camper…don't worry. In the scheme of things, it didn't matter all that much in the long run.
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Old 03-25-2016, 01:17 PM   #4
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Yes, we have another application that we use a single stage charger to maintain the battery charge and for the first year have been able to keep the AS batteries charged with the SSC. However, two points. The cost to go multistage is about $200 if you DIY and our local dealer will do the install complete for $500 if you can not DIY. That is not much of an investment. The MSC lets you dodge the must shutdown charge periodically. Note, this is confusing for a lot of folks and there are a lot of systems to learn on an RV. I would agree that you can get by without the upgrade and if it is something you can afford, it should be installed at initial purchase to reduce the complexity of the systems. Thanks for the alternative perspective. Pat
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Old 03-25-2016, 01:22 PM   #5
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Originally Posted by PJohnson View Post
[FONT=Calibri][SIZE=3]
Now for the real question. How do we keep from cooking our batteries when we are driving across the country and our tow vehicle is putting out 14.4 volts constantly? Note: the Battery Disconnect switch does not isolate the battery from the tow vehicle.
1. People seldom drive across the country or travel for long time periods so the actual effect of the apparent overcharge is very minimal.
2. The voltage from the TV is not a constant 14.4 volts, but varies with temperature and battery situations. There is a voltage regulator built into the TV alternator. TV batteries would be damaged by the millions if this were a real issue. It is not.
3. The voltage drop in the TV to trailer connection system and wiring also reduces the voltage to the trailer.
4. Flooded cell batteries are reasonably tolerant of overcharge if it is not for long time periods, such as days and days. AGM batteries are less tolerant of those situations, and manufacturers of them often recommend disconnect of charge from TV hookups.
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Old 03-25-2016, 01:34 PM   #6
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Just to add a bit of fuel to this fire....... A constant charge level of 13.6VDC will never completely charge a battery........ ANY BATTERY!

It would be a float charge for an appropriate lithium, but lead based systems require 14.2-14.4VDC (Lifelines) or up to 14.8VDC for certain flooded cells per the respective manufacturers recommendations.

As far as 'need'........no one needs to do anything! Just don't complain about truncated battery life if you won't follow the battery makers' requirements.


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Old 03-25-2016, 01:47 PM   #7
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The reason for the single stage charger in Airstreams is that they are the very cheapest device made in China Airstream can buy, just like the GYM ST225/75R15D tires they put on the trailers.
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Old 03-26-2016, 08:30 AM   #8
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The reason for the single stage charger in Airstreams is that they are the very cheapest device made in China Airstream can buy, just like the GYM ST225/75R15D tires they put on the trailers.

Just like every other RV manufacturing outfit out there. They all use the same off the shelf systems and components. I was recently reading a bit on the Provost forum. Million dollar true luxury coaches and guess what, their owners have the same complaints and issues as Airstream owners. And just like Airstream Provost sells every unit that they can produce.
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Old 03-26-2016, 08:44 AM   #9
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If I plug into shore power no matter what I do with the battery disconnect switch manually, the switch turns on and I cannot turn it off until I unplug from shore power.
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Old 03-26-2016, 08:52 AM   #10
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If I plug into shore power no matter what I do with the battery disconnect switch manually, the switch turns on and I cannot turn it off until I unplug from shore power.

When you plug in to shore power that light is on to tell you you're plugged in - even if you switch it to "store" it will stay on until you unplug from shore power. It's a weird setup!

Here's the text from my manual (2012 Flying Cloud)

BATTERY DISCONNECT SWITCH
The disconnect switch is used to separate the batteries from the 12-volt distri- bution panel and converter charging system.
When the switch is turned “use” (on) and the trailer is plugged into a 110-volt shoreline, the 12-volt distribution panel will receive power from the converter G and the batteries will be charged through the converter charging system.
When the switch is turned to “store” (off) and the trailer is plugged into a 110-volt shoreline, the 12-volt distribution panel will still receive power from the converter, but the batteries are disconnected from the system. The batteries will not be drained with the switch in the store position. The converter will not charge the batteries with the switch in this position.
The charge in the 12-volt batteries is replenished when towing from the tow vehicle alternator through the 7-way cord. This charge will go to the batteries no matter which position the Battery Disconnect Switch is in.
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Old 03-26-2016, 09:03 AM   #11
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I leave my trailer plugged into shore power year round. The old univolt did cook the water down low one time.

When I converted it from 30amp to 50amp, I used the new PD4500 series power panel (the 60amp in reality, but they call it a 50amp...may have been the same model the OP mentioned....I don't recall) with the Charge Wizard. I've never cooked a battery since and it seems to keep them topped off just fine. I've been happy with it.

What I really like is being able to run the a/c, the microwave, and the toaster at the same time
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Old 03-26-2016, 10:06 AM   #12
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If you are contemplating a solar upgrade in your future then it's not necessary to swap out your converter for a three-stage converter since your solar battery charger will likely be equipped with a three-stage charger. When you do this you'll simply keep your Use/Store switch in the Store position even when connected to shore power. This will disconnect your converter from overcharging your batteries.
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Old 03-26-2016, 11:19 AM   #13
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We still have the original converter/charger and factory solar/AGM batteries in ours, working fine after 4 1/2 years 1100 nights camping. As stated above, the USE/STORE switch allows the stock converter to power the Airstream with external power, while the solar keeps the batteries up.

This is not to endorse the factory solar as a great boondocking setup, but for travel and used with a generator as needed the factory systems have all worked out for us.
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Old 03-26-2016, 11:26 AM   #14
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One point to make. If you are using the USE/STORE switch when stopping for the night on external power to isolate your batteries, don't forget to put the switch to USE position in the morning so the refrigerator can operate on propane after removing external power.
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