Wattage on a Converter

[Bob Landry]

How is power figured on a converter? For instance, a 45W converter, if it's figured on output, would only be putting out a little under 4Amp at 12V. Am I looking at this correctly?

[Festus2]

Bob-
My understanding is Watts=Volts X Amps. In the example you cited, yes it would work out to 3.75A at 12 volts.

[PARAPTOR]

Originally Posted by Bob Landry

How is power figured on a converter? For instance, a 45W converter, if it's figured on output, would only be putting out a little under 4Amp at 12V. Am I looking at this correctly?

Yes, if I had a box with a rating of 45W. I would assume it was the OUPUT rating and if box was 12Vdc output then yes little under 4 amps outpuT. MOST converters I have seen were rated based on AMPS (exp 45A) out. With under 4amps achievable with a simple output diode bridge.

[Bob Landry]

Thanks, I thought that's what it was. it just didn't seem like 4A was enough to power all of the overhead lights and controls for the appliances.

[Festus2]

Bob-
How did you determine that the converter had a rating of 45W? I'm with you, I don't see how, if its output is 3.75 Amps at 12 volts could possibly power all the lights plus other "stuff". Each one of those incandescent lights probably draws about 2amps ...

So you can see that 45watts won't get you very far. Surely, the converter puts out far more amps than 3.75. At this rate, it would take forever to even charge your batteries. If the converter's output is 3.75 amps, I don't see how any of the items that use 12v could possibly run.... lights, fridge, furnace fan, water pump,........

Something is amiss in the 45 watt converter rating.....??? I checked my WFCO manual and can't find any information there about its wattage rating.

[Bob Landry]

You'll get no argument out of me on that one. It seems a little light to me also. I'll call Monday and see if I can get some clarification. The main thing I want to know is how much AC current it's drawing and my EMS will tell me that. I'll just turn on everything I can and what ever it draws, I'll call max..

[Bob Landry]

Duh!!! <Slapping forehead> It's a 45 Amp converter, not 45 watts. I think I've got too many projects going on.. The input power is 780 watts, so at 115V, that would be a little under 7A.

[PARAPTOR]

When question came up I assumed Bob was working on some project Because of amperage capacity I assumed he was not referring to his rigs main converter His main converter has to be much larger than 4 amps

[Festus2]

Bob-
If the converter is rated at 45 amps which makes much more sense and you have 110v input, doesn't that work out to a maximum wattage output of 4950 ? (watts = amps x volts). I guess this would be its AC rating but not sure how relates to its DC output.
Perhaps someone with electrical expertise can figure this out for me and explain it in simple terms will chime in.

I realize the converter has two "sides" to it - one for AC and another for DC. How do you figure out the amp output for the DC side?

Please, no theories or speculating. Thanks.

[Bob Landry]

From the 45A converter specs on WFCO's website. Mine is the 8900 Series, 45A Converter.

[PARAPTOR]

Festus2,

Would be same as you stated in your post

Max Converter output is 12V X 45 Amps 540 Watts


If you notice, these converter are feed off 115VAC breaker rated at either 15 or 20 AMP .

Not sure how the reverse polarity fuse is sized

[Festus2]

According to my WFCO owner's manual, there are two DC branches/circuits within the converter: one designed for a maximum of 20 amps (fused) and the other designed for a max of 30 amp (fused)

There are also two 110V AC circuits: the main one rated at 30A (breakers) and a branch circuit rated at 20A max (breakers)

There is no mention of the wattage in the manual but it is apparently available on the website.

I am still at a loss as to how many amps the converter produces on its 12V DC side. Does the 7.5 amp mean that each separate DC circuit produces 7.5 amps? Surely, it can't be the total of all the various circuits. Even 7.5 amps seems a bit on the low side for a single circuit.

Still waiting to hear from someone with electrical expertise who can shed some light on this.

[Bob Landry]

Festus,

The website listed the DC output for a 45A converter at 45amps at 12VDC. That's just the DC side. Keep in mind that the AC portion of the converter is nothing more than an AC distribution panel with a breaker feeding the converter and also the other AC loads in the trailer. It doesn't appear that the AC portion of the unit has any bearing on figuring the DC output of it.

[Festus2]

Bob -
Well that makes much more sense and I'm guessing that's why they call it a 45A converter! Now I can see how it is possible to have the lights on, run the pump or flush the toilet and turn the furnace on. I guess I was too hung up the wattage produced when it really doesn't matter that much -- it's the amps that count.

[Bob Landry]

One thing has my curiosity. The converter also serves as a battery charger so is the 45A(my converter) all inclusive or is the battery charging part a separate function in addition to a 45A output? There are 30A fuses to protect against reversing the battery connections. If the battery is turned off, does the converter still produce the full 45A?

[JRTJH]

Bob,

You're right. The input is 120 VAC 30 amps to the main breaker. There are "up to" 5 branch AC circuits. One of those is rated at 15amps and feeds the converter. Others feed the HWH and A/C, etc....

The converter "INPUT" is 120VAC and it consumes (at max power) 780 watts. That is 6.5 amps (of 120 AC). to produce the DC power.

The 12 VDC is really a "nominal 13.6 VDC" rated at a maximum of 45 amps which is 612 watts of DC power.

That is divided into 11 DC circuits, each fused with a 15 Amp DC fuse. (those can be changed to higher or lower amperage if the wiring connected to each DC circuit is upgraded or downgraded) ** the maximum is 20 Amps at each circuit**.

The battery charge circuit is a 3 level charging circuit, Boost= 14.4VDC, Absorption=13.6VDC and Float= 13.2VDC. Somewhere I read that the maximum charge amperage is 40 amps, but I can't find that reference now...

There are two "reverse polarity protection fuses" rated at 30 amps. They do not protect any output circuitry, but only serve to protect the 12VDC input from the battery against reverse polarity. They are not connected to the 12 VDC output side of the converter.

Hope this helps more than it confuses......

[PARAPTOR]

Sorry about delay internet hung up

Festus2.
Sorry but I have no idea what you are looking at?? two DC outputs , two 115 VAC circuits ?
OK (know you want to hear from someone else, But)
HERE, I will put it another way
Converter converts AC to DC
My Converter is powered from a 120VAC Breaker (AC side)
According to the manual Converter has two output terminals only (+ and - ) (DC OUTPUT SIDE)
Since we are going to be playing with AC and DC power for this calc will VA
For calculation purpose lets use 12VDC output at 45 AMPS (540 watts)
input AC Voltage is 120VAC
Assuming we had a converter that was 100% efficient...
Input 120 VAC current would be 4.5 AMPS
More realistic 80% efficiency would give you 5.63 AMP

Therefore for this calc Converter 80% efficient would put out 12VDC at 45 AMPS and require an 120 VAC input of 5.63 AMPS

That is how you look at power on the input and output sides

My converter actual Nominal output is 13.7 VDC
Now this singe 12VDC output feeds a distribution block (maybe that is what you were referring to???)

Hope you get your answer from the one you are asking to respond


Just my 2 cents

[Festus2]

Originally Posted by PARAPTOR

Festus2.
Sorry but I have no idea what you are looking at?? two DC outputs , two 115 VAC circuits ?
OK (know you want to hear from someone else, But)

Converter converts AC to DC

Hope you get your answer from the one you are asking to respond

Just my 2 cents

Yes, I am well aware that the converter "converts" AC to DC. In the manual, it makes reference to two output DC circuits - circuits 1-9 and circuits 10-11. I know the function of each of those two circuits. That is what I was referring to when I spoke about 2 DC circuits.

If I understand the manual correctly, there are also two 120V AC branches : one main one rated at 30 A , the other rated at 20A.

I think with the input from you, Bob and John I now have a better understanding of the "inner workings of the converter". I don't fully understand it and I really don't feel any burning desire to. At this moment, I am suffering from "information overload".

Poking around electrical panels armed with a "little bit of understanding" is, in my opinion, a dangerous thing to do. I don't pretend to have enough knowledge or experience to either give advice or do my own diagnostic troubleshooting should the converter require repair or servicing. I'll get someone who knows what they doing and confine my electrical expertise to changing my lights to LED's. I've already done this without harming myself or others.

Again, thanks for your input and I am not looking for anyone to further enlighten me -- I have seen the light - dimly mind you, but it is there somewhere.