Peter, thanks for such a prompt, detailed input. I need to add immediately that I was using kva and watts interchangeably.........

1) "For Watt demand you Multiply Amps By Volts. But you must have the right voltage."  Yes I did the following: 25 A charger X 17.7volts (I'm going on the back panel here..) = 442.6 W.   So, perhaps 480 watts including 10% efficiency gain. In theory, the 1kva Yamaha generator should have no difficulty covering it. However, the guy I wanted to buy the charger from said that, from (his) memory, the unit drew 900Watts. He said the way I had worked out watt rating was wrong. Hence my questions. Is the 900 watts a continuous draw, do u think? How does one get the 900w figure????

"[3]Aaaah, now we have a diificult one.  Do you sleep inthe trailer ? Yes

"Is the charger just going to be plugged into an outlet & connected to the batterries?"  Yes, in every instance, the charger will be connected to the AC from the generator and connected to the batteries via Anderson plug for the sole purpose of charging the AGMs..............Nothing else will be plugged into anything else at this time. How do I get the 15 amp outlet with its bigger earth slot on the genny reduced to accept a 10 amp plug from the Ctek??!! Or any other 10 amp plug, come to that (TV , laptop charger etc.)!!

Tiyul wrote:

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Hi, good people. I have a couple of questions maybe somebody could help me with.

1) I want to run a 25 amp Ctek smartcharger to charge total 220Ah AGMs.

What is wattage draw for charger? For a 40 amp charger?? Could somebody have a go at writing out the calculation as well??!!!!

2) will a 1kVa Yamaha/Honda genny run the 25 amper, or is it cutting it a bit fine?

3) I am also considering a 2kva generator. Apparently, and I have no RV experience, they have 15 amp AC outlets. I pull a 7x5 trailer where I have my batteries etc., so no fancy motorhome etc..

My silly question is: because the generator has a 15 amp AC outlet, I need to plug in a 15A lead: how do I then attach a common or garden 10 amp charger plug or even a power board to this set-up?? The solution may be blindingly obvious to most of you, but I would appreciate any and all help!! Thanks

OK, that was 3 questions; now u understand why I have these issues with simple math....

Here is an el cheapo which looks about right specs wise. Any opinions/experience??

http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&item=161114542976&ssPageName=ADME:B:WNA:AU:3160

 

 

-- Edited by Tiyul on Wednesday 2nd of October 2013 11:29:08 AM

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 HI Tiyul

For Watt demand you Multiply Amps By Volts

But you must have the right voltage In the case of  it is not the battery voltage for a 12V charger it would be more like 17V

40A x 17V =680W

Now the input wiil be a liitle higher possibly around 5<10% depending on efficiency

680 +68=748W

[2]Now that is tricky  generator ratings need to be understood

They can often be advertised with TWO ratings

[a] The MAX short term [SURGE] rating {Watts} for how long ? it MAY be from a minute or two <to 30 mins

The "CONTINIOUS RATED power That is the power it can safely deliver indefinately without burning out

I

Now the problem with KVA rating is that it is not the same as WATTS

It is Volts by Amps by POWER FACTOR

Power factor can vary over a wide range  but typicaly between 50% up to 100%

100% is only obtainable with purely RESISTIVE loads [fridge heater s, incandescent lights]

Fluorecent light, motors , power converters etc all have less than 100% PF

Having said all the above a ONE KVA continious rated generator should be just OK for a 40 A charger 

[3]Aaaah, now we have a diificult one

Do you sleep inthe trailer ?

Is  the charger just going to be plugged into an outlet & connected to the batterries?

NO 240V FIXED wiring?  

But straight up front,,the use of  multiple  outlet power boards IS NOT APPROVED UNDER AUST STANDARDS IN THAT SITUATION.

I'll leave those who may have used the one in the link to comment

But just rember the outside appearance means nothing

It is the QUALTY inside that counts

PeterQ

HI Tiy

RE "However, the guy I wanted to buy the charger from said that, from (his) memory, the unit drew 900Watts. He said the way I had worked out watt rating was wrong. Hence my questions. Is the 900 watts a continuous draw, do u think? How does one get the 900w figure???? "

He is probably getting cofused with KVA

Depending on design the unit supplying 25A @ 17.7V  could have a PF [power factor] of 80%

That would make it's KVA demang on the souce[generator]25 x17.5 x 100/80=0 .553KVA

One other point with KVA & KWatts

The KVA rating is always a higher figure than the KW for the same unit.

If you are soley using the generator to supply the charger or Only plugging an extension lead from the MAINS directinto the charger you have no problems

As PeterD has pointed out there is no problem pluging a 10A plug into a 15 A socket ,Quite acceptable ,BUT the reverse is not acceptable

PeterQ