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Old 10-13-2009, 08:57 PM   #1
Art-n-Marge
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RV converter

Something hasn't been making sense here. I have seen posts about this previously but I am finally gonna ask for some help on understanding this.

I understood most RVs do not need batteries. I only say most RVs just in case there is that one or more exception. But from what I can tell, the batteries always seem to be a dealer added option and even if added at the factory, it's because a customer wants it but the RV doesn't need it but is ONLY needed to boondock and have only 12v availability when a power pedestal isn't available. Therefore when the RV is plugged into shore power the converter will run all 110v AND 12v equipment in the RV. Now if equipped, any batteries are trickle-charged up to the point of being fully charged but there should be no amperage draw from the batteries as long as the shore power is available, other than natural discharge from idle batteries over time.

There have been several posts that while the converter is running fan noise or other "problems" occur (I don't remember any of the other conditions but there are some). I have seen that some replies from members are that this is caused by the batteries being recharged more because using 12v devices puts more demand on the batteries. But if the batteries are not needed and the converter recharges any batteries as part of its normal operation, then the batteries should not be discharging while connected to shore power with any kind of frequency to cause rapid battery discharging therefore causing the converter to heat up and start the fan.

I believe fan noise is caused by excessive heat caused by any RV device usage and not by battery discharge. I think it's the 12v DC devices which can make a converter work harder and get hotter than 110v AC devices. It's been a long time ago, but I think I remember that direct current cause more heat than alternating current on a power supply (in this case an RV converter). I agree that as the weather gets colder and one runs the furnace, the 12v demand will create more heat on a converter than an Air conditioner running 110v AC power and this could be causing the converter fan to run.

I don't remember the other converter problem details posted in the MOC forums but these should still be caused at the converter and not the batteries, as well.

For you (RV) electrical experts, is this correct? What am I not understanding, if anything?

Thanks, all!
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Old 10-14-2009, 03:12 AM   #2
Tom S.
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Art, I believe the system is set up so all 12 volt items run directly off the battery(s) and not the convertor. The battery is capable of handling power draw (surges) that would exceed the convertor's output. For example, the motor that opperates the slides hydraulics by itself comes close to exceeding the convertor maximum output. So in essance, all 12 volt items draw from the battery and the convertor monitors this draw and recharges accordingly. In times of heavy battery useage, the convertor runs at maximum output which creates more heat and causes its fan to kick on.

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Old 10-14-2009, 03:43 AM   #3
H. John Kohl
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Art,
Tom S. beat me to the reply and is right on the mark. You made one comment that many others make.
Quote:
quote:Therefore when the RV is plugged into shore power the converter will run all 110v AND 12v equipment in the RV.
The converter does not provide the RV with any 110vac and therefore does not run any 110v equipment. The converter uses 110vac converting it to 12vdc. The plug in the wall outlet is the only place where the converter touches both voltages.
To finish this thought an inverter can provide 110vac from a 12vdc or other battery source. Converter and inverter are different.

As Tom S. implied the converter supplies 12vdc and refills the battery.
EXNAVYDIVER had to have his converter replaced, it is rated at 75 amps. The battery is rated at more than 75amps and can provide it for a short period of time.
Here is another way of looking at the battery. Consider the battery a water tower in a town and the converter a pump that fills the water tower back up to the full level when needed. The water in the tower is similar to current and voltage in the battery. The water tower can provide more water and pressure at one time than the pump can. If a large amount of pressure is needed for 10 minutes from the water tower it will take the pump an hour to replace the water used in 10 minutes. If the uses is less then what the pump can provide then the tower does not loose any volume. I hope this is not too confusing.

Batteries are provided at the dealer because they should not set in an RV for a year or two until it is sold. They have a shelf life so the dealer installs them instead of the factory.

Because of the pump effect I plug my unit it as soon as I stop and unplug it the last thing before I leave. Therefore, letting the converter provide as much 12vdc as it can for the slides and landing legs allowing the battery to keep as much of it charge as possible in case it is needed when I do not have 110vac around.

I hope this helps.
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Old 10-14-2009, 03:59 AM   #4
Exnavydiver
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Very good analogy John, I might also add that your rig is NOT designed to run without 12 volt. Your rig needs 12 volt power to power the circuit boards on your fridge, your furnace, water heater, and again fridge need 12 volts to power the igniters for the gas burners, and the propane and CO detectors need it for their power. As John said the slide pump and landing gear motors are also 12 volt units. The fan on the converter kicks on when the converter is working hard to "catchup" with the current draw from the battery. While talking to the tech from IOTA the other day he stated that a converter should be rated at about 10% of your rated battery current. 75 amps for a battery rated up to 750 amps and so on. I asked about two golf cart batteries and he said a 75 amp unit would handle 4 6volt golf cart batteries easily... Dave
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Old 10-14-2009, 04:13 AM   #5
IAMontana
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Art,you are part right and Tom is mostly correct in what he said. Look at how your converter and batt. are wired, the converter is pluged into an a/c source then the converter transforms the a/c current into d/c current which is then transmitted to your batt. which provides the 12 volt power source to your 12 volt fuse block. You are some what correct in saying todays rv's do not need a batt. this would be true if you did not have high amp draw components on/in your rig like the jack legs slide motors/pumps furnace motors. With out the batt the converter will run most of the these items but it would not be long before it blows the main fuse or fuses on the converter. The batt. is the main power source for your rig the converter is the power source charging the batt. So if you had a rig with no slides, power jacks and limited lighting with todays converters of 55 amps or more output you would be fine with no batt.. In the old days that was the way it was the converters then only had an output of 35 to 45 amps and did not shut down when the power was not needed or when the batt. was charged that is why you had to watch the water level in your batt. closly back then as the converter would boil it dry. Todays rv's require so much more power that the converters had to have higher amp outputs to keep up with the demand. They are also smarter in that some brands have built in brains to monitor the batt. as to not over charge it. The batt. handles the large surges that the converter can not handle. If you take an amp meter and place it between the converter and batt. then turn on a light you would probably see the same or close to the same output from the converter as the light is drawing but if you have a lot of lights or a fan going you would see the converter put out less power than the high amp draw from the batt. it seems like the converter is running everything but it is not. Hope this helps.
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Old 10-14-2009, 04:39 AM   #6
SlickWillie
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Quote:
quote:Originally posted by IAMontana

Art,you are part right and Tom is mostly correct in what he said. Look at how your converter and batt. are wired, the converter is pluged into an a/c source then the converter transforms the a/c current into d/c current which is then transmitted to your batt. which provides the 12 volt power source to your 12 volt fuse block. You are some what correct in saying todays rv's do not need a batt. this would be true if you did not have high amp draw components on/in your rig like the jack legs slide motors/pumps furnace motors. With out the batt the converter will run most of the these items but it would not be long before it blows the main fuse or fuses on the converter. The batt. is the main power source for your rig the converter is the power source charging the batt. So if you had a rig with no slides, power jacks and limited lighting with todays converters of 55 amps or more output you would be fine with no batt.. In the old days that was the way it was the converters then only had an output of 35 to 45 amps and did not shut down when the power was not needed or when the batt. was charged that is why you had to watch the water level in your batt. closly back then as the converter would boil it dry. Todays rv's require so much more power that the converters had to have higher amp outputs to keep up with the demand. They are also smarter in that some brands have built in brains to monitor the batt. as to not over charge it. The batt. handles the large surges that the converter can not handle. If you take an amp meter and place it between the converter and batt. then turn on a light you would probably see the same or close to the same output from the converter as the light is drawing but if you have a lot of lights or a fan going you would see the converter put out less power than the high amp draw from the batt. it seems like the converter is running everything but it is not. Hope this helps.
I think you described the operation very well. I copied a little info from the Iota site: [The IOTA Power Converter/Battery Charger converts 120 volts nominal A.C. to 13.6 volts D.C. As a power supply,
its tightly controlled regulation allows the user to operate any 12 volt nominal D.C. load up to the converter’s rated output current.]

Being the converter and the battery are tied together, I don't see how the battery is providing any current as long as you don't surpass the current output of the converter. It is merely similar to a capacitor in an AC circuit.
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Old 10-14-2009, 05:20 PM   #7
Waynem
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I'm not 100% sure on this, but I think all 12v systems are powered from the battery, even when the convert is turned on. I don't think the wiring from the converter can handle the amperage at full load, but your battery wires can, and distribute the voltage/current (through something) Through isolation diodes, the converter only provides voltage/current to maintain a charge on the battery.

Am I all wet on this one? Must be something I just don't understand.

Edited: Okay! I'm all wet on this one. I just did not think a converter could handle the full load current like a battery could and would then rely on the battery. Hey, I learn something every day, but what do I know, I'm an S.O.B.
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Old 10-14-2009, 05:38 PM   #8
H. John Kohl
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Quote:
quote:Originally posted by Waynem

I'm not 100% sure on this, but I think all 12v systems are powered from the battery, even when the convert is turned on. I don't think the wiring from the converter can handle the amperage at full load, but your battery wires can, and distribute the voltage/current (through something) Through isolation diodes, the converter only provides voltage/current to maintain a charge on the battery.

Am I all wet on this one? Must be something I just don't understand.
No Wayne that is not correct. The battery is wired to the convert and the 12Vdc fuse panel.
Either can provide 12VDC and as ART has stated the converter can do it by itself.

I feel the converter and battery are a system and both complement each other making a full service device.
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Old 10-14-2009, 09:23 PM   #9
firetrucker
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It might help to think of the converter as just a special battery in parallel with the other batteries. It maintains a constant output voltage up to its maximum current capacity, after which its voltage drops off, it overheats, a fuse or breaker blows, or it destroys itself.

If the converter and the battery have the same output voltage, they both supply more or less the same current to the load.

As the battery volatage drops, the converter must also supply some current to the battery to bring its voltage back up to 13.6 volts. The internal resistance of the battery and the resistances of the cables work to keep all of this in balance.

This goes on until you overload the converter and the smoke escapes, and everyone knows that it's the smoke that does all the work.

Bob
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Old 10-15-2009, 05:42 AM   #10
SlickWillie
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This is something I missed the other day on the Iota site. [Can be used with or without a battery When used as a converter/power supply, the IOTA power converter will only supply what is required by the load. When not in use it is essentially off, reducing electricity usage.]

Another interesting tidbit of info: [Multiple units can be operated in series or parallel to increase voltage or amperage.]

One other thing; I believe the converter voltage (13.4) is higher than the standing battery voltage. IIRC, that is in the range of 12.6-12.8 volts.
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