Charging Battery While Dry Camping Questions

[ve1hup]

Hi,

A little background information first and then my questions for anyone that can help...

This spring my wife and I are moving up from a popup to a new travel trailer and have I some questions about charging that I have had for years, but never needed answering before now.  Most of our camping was and will be dry camping (no hookups.)  To extend battery life, I bought myself a Honda EU1000i generator and a 10/30 amp digital intelligent charger a few years ago.  With the popup, the only thing dependant on 12v was the lights, so it was easy for me to disconnect the battery completely from the trailer when I charged it.  I never knew if the charging voltage might damage the converter, so I never left it to chance.

With the new TT, 12v is needed for the refrigerator, water pump, etc. and disconnecting the battery completely for a few hours to charge it would not be a great.  The new TT has a WFCO WF-8955AN 55 amp converter (http://www.wfcoelectronics.com/docs/manuals/8955%20Manual.pdf).  The manufacturer is a little thin on details of how many amps this converter can deliver to the battery on the charge circuit, and has not replied to my email, so I am unsure if the converter can/should replace my intelligent battery charger.  So, here are my questions:

1) Does anyone know if this converter is a good battery charger (and I know most are not)?  I know from reading the document in the link above that is has a 3 stage charger.
2) If I wanted to use my intelligent battery charger, would I need to isolate the battery from the trailer (i.e. disconnect it as I had done with the popup)?  My charger is similar to this one: http://store.schumachermart.com/25ampchsc.html  I believe that voltage peaks around 15 volts when charging.
3) If I wanted to use my intelligent battery charger, and did not need to isolate the battery from the trailer, would plugging the trailer into the generator (shore power) at the same time cause a problem?  My gut feeling is that this is a bad idea as both the converter and intelligent charger would be hitting the battery.

Any help with these questions would be greatly appreciated.

Thanks
Darryl

 

[Ned]

Being a 55A converter, I would expect it to deliver up to 55A to the batteries when charging.  Since it's a 3 stage charger, you won't need the separate charger any longer.

 

[Gary RV_Wizard]

Well, it claims to be a 3 stage charger and that is goodness and generally indicative of a higher quality unit.  Typically these units balance their rated output between battery charging and supply to the fused output circuits, with one or the other having priority under various circumstances. They don't mention a priority scheme, but that doesn't mean there isn't one. So, it's hard to say whether the full 55A DC output is ever available for charging, but most of it probably is. But if there is little power being drawn on the other circuits (fridge, lights, etc) then most, if not all of the 55A is probably available for charging.

However, "available" rarely means it is actually charging at that rate. In fact, it would never do so except when in bulk charge mode, which happens only when the battery is low in charge and ends in fairly short order as the voltage comes up. As soon as the charger shifts to absorption mode you can bet the charge rate drops substantially.  That's why you can re-charge a battery to 75-80% of capacity in a few hours but it takes 24-48 hours to get that last 20%.

If you want to use the other charger (I wouldn't, by the way), turn off the converter if you can or disconnect the battery charge leads if you cannot. A battery switch on the positive charge wire would do the trick. The reason is that both chargers are sensing battery voltage to determine the state of charge and having two chargers throwing voltage into the battery will confuse each other, most likely causing both to thing the battery is already fully charged.

 

[ve1hup]

Thanks very much for the information.  Well, *if* it was to actually deliver 55 amps to my battery, I think my 1000w genset would overload.  I may have to start to think about upgrading it as well.

Darryl

 

[Gary RV_Wizard]

I think my 1000w genset would overload.

Not likely from that load alone. 55A @ 13V = 715 watts, which is still a couple hundred less than an eu1000i will deliver continuously, right? But I agree that adding additional loads might push it over the edge.  Remember the rule of thumb: each DC amp takes only 1/10 of an AC amp as source power.

 

[Lou Schneider]

They don't specify the maximum voltage in bulk mode.  My suspicion is the charger has two voltage levels, 13.6 and 13.2 volts and alternates between them.  I suspect the "bulk" charging mode is simply current limiting that restricts the voltage to less than the maximum 13.6 volts if the battery wants to draw more than the charger's rated current.

If the converter does, indeed, limit it's voltage to 13.6 volts you will not get anywhere near 55 amps into one or two batteries. The voltage would have to be significantly higher, in the range of 14.5 volts, to get that much charging current into a small battery bank.  I doubt the charger does this.

Before you replace the generator, run the batteries down, plug in the trailer and see what happens.  I'd guess your charging rate will be more in the range of 10-20 amps per battery, well within the capacity of an EU1000i.

 

[heed71]

I would tend to agree...I doubt the wiring in the trailer is rated to take 55A of DC current for periods of time. All that a multi stage charger does, is allow you to put in heavy bulk charge without screwing up your battery. It then backs off the charge rate at pre-determined points to finish it off and that's what takes the longest.

I don't think, as a weekend camper, you will ever have any issues, but if you are out for a week somewhere, you will definately have to put some back in at some point. Your generator should adequately cover that. Since I don't have a multi stage charger, I sometimes plug my truck into the trailer when I want to charge a bit faster.

Rob
2003 Trail Cruizer 26QBS
2000 Nissan Pathfinder

 

[John From Detroit]

This is for Lou,  Re Bulk charging,  Yes, when you first begin charging the system goes into bulk mode, this limits the current to either the max for the charger or the max for the batteries (I have two battery banks here, fully independent, one maxes out the charger)  As the voltage rises it switches to absorption mode, this limits the voltage  So actually stages 1 and 2 of charging use the same voltage and current limiters (in most cases) IF you would like numbers I can pull them from my xantrex manual.

Now in the absorption mode as the battery "Absorbs" it's full charge current will trickle down to zero or near zero, at this point the converter switches to "Float" voltage (The lower voltage) which means that battery current should now be zero, with the converter powering all loads. (In practice there may be some battery current, and some converter/chargers will still continue to charge beyond "FULL" this may or may not be an issue depending on how much and how long.)

Here is one line of the Xantrex manual, Generic Flooded Wet Cells

Bulk/Absorption Max V 14.4  Max I (Current) 30% of capacity,  Float Max V 13.5  Equalize 17.5

Equalize is done on request only by Xantrex.  Charge Wizards do it automatically.  It is a brief overcharge.

On the current.... 30% capacity means if you have U-220's with 220 AH capacity it's 66 AMPS.

As the battery voltage rises... Current naturally goes down


Oh, and I forgot one other thing... Temperature,  As the battery gets hotter or colder it's charge requirements change

Xantrex automatically adjusts the charge voltage according to temperature.

 

[Lou Schneider]

Yes, when you first begin charging the system goes into bulk mode, this limits the current to either the max for the charger or the max for the batteries (I have two battery banks here, fully independent, one maxes out the charger)

Another way of saying "max (current) for the batteries" is to say the charger lets the current determine the voltage level until the voltage reaches a pre-determined point.  Usually this is around 14.4 to 14.5 volts.  Then the voltage stabilizes (does not rise any further) and the current decreases while the battery gains a charge.

The problem is nowhere in the documentation, including the troubleshooting section, does this charger manual mention anything above 13.6 volts.  At 13.6 volts you'll get about a C/10 "bulk" charge rate, which is 10 amps for a 100 amp-hour battery, 20 amps for a 200 amp-hour battery bank, etc.

 

[ve1hup]

Thanks for all of the great responses.

Darryl