I go by the Amp's fuse rating.

Most (or all) amps are provided with Slow Blow type fuse (those are indicated by letter 'T' [Time] associated with its current and voltage rating) .

Why 'Slow blow' ? As I mentioned above amps take higher current at cold start (that is when you swict on the amp ) as well as during delivering complex music sections, while normal steady state current is much lower.

If a fuse is fitted in accordance with the steady state current , it will blow during start up and dynamic deliveries, while fuse rated as per the In rush current won't protect the amp when it operates at steady state current (most of the time. )

Slow blow fuse can take a momentary excess current load than its rated current this helps to tide over in rush current demand , hence the fuse won't blow while under normal conditions if the amp tries to draw excessive current over a longer period the fuse blows and protect the amp.

Slow blow fuse can withstand 2-3 times normal rating that is printed on the fuse. So take this steady state current fuse rating and mutiply by 3 to arrive at worst case current drawn by the amp. Then multiply it by 230 to get KVA rating. Then multiply it by 1.2 to comensate for power factor, assuming that amp's input transformer is having 0.8 lagging pf. This will give you a correct estimate of actual KVA requirements , agian multiply it by 1.3 to have some safty buffer. Now you know what KVA stab to order!

Here I am considering only Amp, if you have any other current hungry equipments also to be powered then add respective VA requirements.

My amp takes 0.8 A under steady state and probably 3 A worst case, I have provided a 3 KVA Krykard servo voltage stabilizer which can supply around 13 Amp.

Hope this helps.

SUhas

Suhas:

We are both talking about the same thing. You can calculate the load from either amperage or from wattage, but both will arrive at the same volt amps. This is assuming that the load factor is the same.

As you mentioned, you can also calculate the load by multiplying the amperage with the voltage - either 110 or 230. Assuming the load factor is the same, you will arrive at the same results. In other words, amp*v/LF and W/LF will be the same.

Couple of things about your calculations:

1. If I am not wrong, a fuse will be rated

**not** at steady state, but to withstand max load. In addition, the system at full load will be only 75 to 80% of the fuses's rated capacity. If this is not done, you will be changing the fuse everyday. Thus. the fuse itself has a good buffer. In addition, if it is a slow blow fuse, it is further capable of withstanding (as you said) 2 to 3 times it normal rated capacity during a in-rush.

2. In-rush and the need for a slow blow fuse is usually meant for lighting elements and motors where there is an inertia that has to be compensated for.

3. In a solid state electronics such as amp, the initial load when you switch on the system is only the quantum of energy needed to fill the capacitor and the time taken to do that. This quantum of energy should not strain the system beyond 150% of its normal load, and the time taken should be less than 10 seconds.

Though there is no harm, I do believe you are being overly cautious in calculating the load for the stabiliser. Actually providing for just the right capacity at the stabiliser end may be more prudent, as the stabiliser will trip or shut down in the event of a overload, thus protecting the expensive audio equipment.

Other than the fact that, in addition to the load factor, you are adding for a buffer at the fuse level, we are both talking about the same thing.