Learn how to size a generator in one of the most common applications.
First the TLDR:
- Two Major Loads – A/C and Heaters
- A/C Draws up to 20A each
- Heaters Draw up to 50A each
- Lights and Electronics are usually negligible
- 20kw Suitable for most trailers in summer
- 50kw suitable for larger trailers in winter
What considerations do I need to make when sizing a trailer?
Sizing a trailer generally pretty straightforward. If you have a small, ground level office for instance, you can get away with a 20kw all year. What makes things tricky is when you have more complex setups and multiple trailers.
- What time of year is it?
- Do you want climate control at all?
- How many heaters are on the trailer?
- How many A/C’s are on the trailer?
What Time of Year is it?
What will the weather be like during your project?
If the project is summer in Chicago, you probably will only be running A/C. If it’s winter in Minnesota you will be blasting a heater.
It might be warm in September, but in two months you’re going to want to use a heater.
Do you want Climate Control at all?
It’s rare, but in some cases climate control just isn’t worth the cost.
In some cases a simple gasoline generator will get the lights for a daily 6AM meeting before everyone hits the jobsite.
How many heaters are on the trailer?
Your biggest load on a trailer is the heater.
In order to keep a heater on you’re going to need 50A at 240 volts.
So let’s image a double wide trailer: You have two heaters, drawing 50A each. That’s 100A total.
A generator with a nameplate of 56kw/70kva produces 45kw/56kva running prime.
Since the generator is a 3 phase generator it will produce 136A.
Generators are designed to run at 80% of capacity so this size would be appropriate.
The next size down would be a 45kw which produces 108A. This will work, but is harmful to the generator over the long term as you’re over 90%.
How many A/C are on the trailer?
The second biggest load is the air conditioner.
A/C can vary but typically draw no more than 17A each.
Let’s take our double wide as an example again.
Two A/C = 17A X 2 = 34A
A 20kw (16kw prime) generator with variable voltages will produce 48A. Giving you a 30% margin.