Which power transformer is best for which construction machine? Compare kVA ratings in this 110V transformer guide. 

kVA = (V x L)/1000/0.8

Using the above formula can help determine which size transformer you require. 

Where V is the input voltage of the machine, L is the current load in amperes and then divide by 1000. The last step is to divide again by 0.8 which represents typical power factor of a load. Note this formula is for 110V/115V machines only. 

Below are examples for some machines sold at Red Band UK:

ProductFormulaRecommended Continuous TransformerRecommended Intermittent Transformer
CM42115V x 26A/1000/0.8 = 3.7375kVA5kVAN/A
TS350/400115V x 14A/1000/0.8 = 2.0125kVA3kVA5kVA
PRIME 100/120115V x 16A/1000/0.8 = 2.300kVA3kVA5kVA
ELITE 80/80s115V x 16A/1000/0.8 = 2.300kVA3kVA5kVA
VIP2125115V x 12A/1000/0.8 = 1.725kVA2.5kVA5kVA
CM35115V x 22A/1000/0.8 = 3.1625kVA5kVAN/A
K4000110V x 20A/1000/0.8 = 2.75kVA3kVA5kVA
K4000 CnB110V x 20A/1000/0.8 = 2.75kVA3kVA5kVA
CM501115V x 30A/1000/0.8 = 4.3125kVA10kVAN/A
BSD45115V x 28A/1000/0.8 = 4.025kVA10kVAN/A

The above formula will give you the absolute minimum kVA rated transformer required, meaning the transformer required needs to be higher than the result of the formula.
When using an intermittently rated transformer ensure the continuous rating of the transformer is not lower than the absolute minimum.

IMPORTANT: There are two main types of transformer available, Intermittent and Continuous. It is vital that the two are not confused. As the name suggests, an intermittent transformer will deliver the specified amount of power on a limited/intermittent basis, whereas a continuous transformer, the specified amount on a continuous basis.

It is also important to remember that running multiple tools simultaneously out of different transformer ports will affect/lower the available power each port has respectively by the power rating of the tool it is running.

Intermittent or Continuous rated Transformer?

Transformers for the most part are supplied with either a domestic 3-pin (13Amp) plug or a yellow 3-pin (16 or 32Amp) Commando plug fitted. Transformers with a domestic 3-pin plug will be intermittently rated, meaning that their continuous rating will be lower (usually about half of its stated intermittent rating).

The rating of a transformer and whether it is intermittent or continuous rated can be found on the labelling/sticker applied to a transformer. Transformers which are rated to be 5kVA continuous or more will not operate correctly off a domestic supply (plug socket) unless they are hard wired directly into the supply.

Machine won’t start? Tripping out or stopping?

There could be a few determining factors as to why your machine is not working, tripping or stopping.

  • Thermal Overload – Most machines and transformers will have a thermal overload built into them. A thermal overload is designed to essentially protect the motor and electrics from overheating/damage as a result of too much current being drawn for extended periods of time.
  • Extension leads – Machines can be used with extension but keep them to a minimum. Excessive extensions will lead to a volt drop. This in turn will increase current demand the equipment will use which can lead to continued tripping and overheating.
  • Stepdown adaptors – Adaptors must not be used. The machines are designed to be used specifically with the plug supplied and should never be changed.
  • Ageing transformer – Transformers degrade over time. Try your machine on a different transformer if experiencing any issues to rule this out as a possible issue.