Outer Limits 4x4 Board

i want something around 15 amps to charge a agm battery? any suggestion and ruff price. i looked at ctek one and they are $400

tazzashort wrote:i want something around 15 amps to charge a agm battery? any suggestion and ruff price. i looked at ctek one and they are $400

they are good tho...

Anything that will do 15Amps isn't going to be cheap. Have a look in Supercheap as they sell some decent chargers- I've got a 10Amp one that can be used as a variable power supply as well.

http://www.projecta.com.au/catalogue/cid/6/asset_id/32/

i got this from bursons for $250 from memory. does 6/12/24 at high current, also has a jump start function

There's only one thing with the above charger:

* The term "20A" as opposed to "12,000mA" is an Amps RMS rating used as an industry reference and not the actual DC output.

It 's a bit like I've only ever seen 7 Amps indicated on the current output of my "10 Amp" charger! Buyer beware!

ebay bargins can be had on the c teks i waited for a while and found one and am more than happy with it

murcod wrote:There's only one thing with the above charger:

* The term "20A" as opposed to "12,000mA" is an Amps RMS rating used as an industry reference and not the actual DC output.

It 's a bit like I've only ever seen 7 Amps indicated on the current output of my "10 Amp" charger! Buyer beware!

Can anybody explain Projecta's comment? Are they trying to say that 20A RMS is really only 12A DC? Or is the 20A figure a peak figure, and 12A is the RMS figure?

Either way, it's a DC output - if it was any good, there wouldn't be a difference between RMS and DC.

Hi tazzashort, here’s another option.

This is a Jaycar product.

http://www.jaycar.com.au/productView.as ... BCATID=295

-Scott- wrote:

murcod wrote:There's only one thing with the above charger:

* The term "20A" as opposed to "12,000mA" is an Amps RMS rating used as an industry reference and not the actual DC output.

It 's a bit like I've only ever seen 7 Amps indicated on the current output of my "10 Amp" charger! Buyer beware!

Can anybody explain Projecta's comment? Are they trying to say that 20A RMS is really only 12A DC? Or is the 20A figure a peak figure, and 12A is the RMS figure?

Either way, it's a DC output - if it was any good, there wouldn't be a difference between RMS and DC.

Straining the brain a bit.... but from my training IIRC RMS is Voltage Peak x .707

But I agree, it's verging on false advertising. You pay for a "20 Amp" charger then you expect it will supply a sustainable 20 Amps to a dead flat battery.

i was thinking the same, RMS only applies to an AC waveform. anyway i think it is a good charger nonetheless. (is that one word?)

ausoops wrote:i was thinking the same, RMS only applies to an AC waveform. anyway i think it is a good charger nonetheless. (is that one word?)

thats correct, you can only take an rms of an ac wave form, and since the power going into a battery isnt alternating i dont understand how you can have an rms value of the current, it should be a flat wave at what ever its charging. Therefore what they are really saying, is that if it arcs between the contacts it can produce 20A then most likly blow something, but in the real world its more like 7 or 12A with a load attached

You can have an RMS of any cyclic waveform. I doubt very much these are pure dc waveforms being pumped out, but close enough to be negligible.

From what I can gather looking at some of their other products specs it seems the 20 amp figure is prior to rectification (ie directly after the transformer), while the 12000mA is the rectified output (ie smoothed output) which probably also takes into account losses due to the rectifier circuit (diodes, caps etc).

Basically I would assume the internal workings of the charger look something like:

240v input, xAmps AC -> transformer -> xVolts, 20amps AC -> rectifier circuit -> 12V, 12A DC.

Or I may be wrong and am thinking more voltage losses. I haven't touched on power electronics for a while.

-Scott- wrote:

murcod wrote:There's only one thing with the above charger:

* The term "20A" as opposed to "12,000mA" is an Amps RMS rating used as an industry reference and not the actual DC output.

It 's a bit like I've only ever seen 7 Amps indicated on the current output of my "10 Amp" charger! Buyer beware!

Can anybody explain Projecta's comment? Are they trying to say that 20A RMS is really only 12A DC? Or is the 20A figure a peak figure, and 12A is the RMS figure?

Either way, it's a DC output - if it was any good, there wouldn't be a difference between RMS and DC.

I may have an answer for these "ratings".

I've been chasing quotes for a few UPS systems at work, and have been struggling to make sense out of some of the offers - capacity ratings and output figures don't add up.

While discussing the issue with one of the companies, the rep explained that power converter companies, particularly SE Asian manufacturers, typically work with a "power factor" of 0.6. This means that, when they convert power to voltage & current (or vice-versa) they throw in a "fiddle factor" of 0.6.

So, my theory: The above power supply, with a 12A DC output, is rated by somebody at (say) 144W - that's 12V x 12A. Then some non-technical person decides that 144W is 240VA (using a 0.6 power factor - for a DC output!) Some other genius (perhaps even the same one?) then takes that 240VA, divides by 12V and they come up with 20A.

See, it's simple really! How stupid are we for not understanding that?

murcod wrote:

-Scott- wrote:

murcod wrote:There's only one thing with the above charger:

* The term "20A" as opposed to "12,000mA" is an Amps RMS rating used as an industry reference and not the actual DC output.

It 's a bit like I've only ever seen 7 Amps indicated on the current output of my "10 Amp" charger! Buyer beware!

Can anybody explain Projecta's comment? Are they trying to say that 20A RMS is really only 12A DC? Or is the 20A figure a peak figure, and 12A is the RMS figure?

Either way, it's a DC output - if it was any good, there wouldn't be a difference between RMS and DC.

Straining the brain a bit.... but from my training IIRC RMS is Voltage Peak x .707

But I agree, it's verging on false advertising. You pay for a "20 Amp" charger then you expect it will supply a sustainable 20 Amps to a dead flat battery.

Correct, for sine waves. It is supplying 20 amps PEAK (measured before the bridge rectifier) to the battery but 12 amps RMS accounting for losses through diodes (and consequent voltage losses) etc.