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Old 07-06-2011, 05:05 AM
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Default Inverter on ct33

I have a 2500 watt inverter in my truck with two deep cycle batteries and two starting batteries with double 00 wiring. The inverter has two 15 amp breakers on it

I tried my ct33 on my inverter today and wanted to post my experiences.

I needed to break a 4x8 sheet down and had no power where I was at.
Every thing was really hot where I was working, I would say about 100 deg in the building where I was working and maybe about 95 in the truck where the inverter was.

I plugged in the ct33 directly to the inverter and turned it on, it had good suction. I set it to auto and set up the guide rail on the plywood.

Then I started to make my cut and nothing happened. I checked the inverter and it said I overloaded it. I turned the ts55 down to 5 and the vac half way down then proceeded to make all the pieces to the width that I needed them. On the last rip cut all the sawdust stayed on the table the last four feet of an 8ft cut.

I thought the bag must be full but when I checked it was empty so I put the vac on manual and I just heard a humm and nothing else happened. I thought I killed my vac so I packed every thing up and went home.

Brought the vac in the house and plugged it in. It worked with full suction. Boy was I relieved.

I had read on here before about the kapex not working with an inverter . But never heard anything about the ct's not working with one.

I don't know what I should go with for backup power on job sites?
Or would a filter work of some kind on the inverter that I already have?

And then would I be able to use my kapex?

Anyone have any ideas?

It looks like I should put some smilies here
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Old 07-06-2011, 06:16 AM
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Default Re: Inverter on ct33

Welcome mishle. I don't recall reading of anyone running the vac/saw on an inverter so thanks for posting your experience here. And welcome to tF.

I don't have any experience with inverters so we'll have to wait for a good answer. Rick?
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Old 07-06-2011, 02:36 PM
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Default Re: Inverter on ct33

I love my Honda generators:

2 Honda eu2000i's with the parallel kit

but I'd be the first to say I haven't tried my Festool stuff out on them. Right now the generators and the Festools are 500+ miles apart. Maybe in the fall..........
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Old 07-06-2011, 03:56 PM
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Default Re: Inverter on ct33

I have a big Coleman 8000w generator that I use my Festools on when I am working on my "Blank Slate" shop building. I never have any issues with it and also ran a rented Bosch "Brute" jack hammer with it for three days last weekend. This is a large generator that I have to haul on a trailer.

I think any smaller generator with at least a 20A circuit breaker would run any Festool without a problem.

And
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Old 07-06-2011, 04:16 PM
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Default Re: Inverter on ct33

If the inverter doesn't have enough inductive filtering on its output, there could be some large current spikes occurring. All of the generators mentioned have their output currents limited somewhat by internal inductance.

Charles
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Old 07-06-2011, 05:03 PM
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Default Re: Inverter on ct33

This sounds like a Rick question to me. Rick?
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Old 07-06-2011, 07:07 PM
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Default Re: Inverter on ct33

A lot of inverters and portable generators don't produce true sine waves, which some electronics require. The best option IMO is a generator rated for 2500+ watts continuous that produces clean sine waves. You can also look for "computer safe" or similar that really means the same thing.
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Old 07-06-2011, 07:21 PM
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Default Re: Inverter on ct33

The type of output from an inverter is going to vary depending on type/quality. Their main goal is to generate a smooth sinusoidal signal, but this is difficult to do with high-power switching transistors. An analogy would be if you had a dimmer for the lights in your home. In order to create a sinusoid, you would need to smoothly turn the dimmer from full-Off to full-On and back to full-Off to create 1/2 a cycle. During those periods where the dimmer is only partially On, the dimmer must dissipate the unneeded energy, and this generates a lot of heat.

Instead, the switches go from full-Off to full-On with nothing in between. It doesn't need to shunt any of the energy for the partial-On conditions so it creates less heat.

I found this simple graphic on the internet. The simplest inverter will create a simple square-wave output, such as shown in the left grid. The desired sinusoid is shown in the right graph. A little closer, is one that has a slight "off time" in the middle.


Some inverters will attempt to simulate the power of a sine wave by using a much higher frequency of pulses and turning them on and off at varying intervals--farther apart for the beginning and closer together near the peaks. This is called Pulse Width Modulation (PWM).


But the problem with any of these outputs is that the EC-TEC controller in the Festool tool is also doing something similar, and controls the amount of power to the motor using a PWM output. This can cause some conflicts between the electronic systems, especially because the EC-TEC switching is expecting a sinusoidal input instead of a series of short pulses.

The type of transistor used with the EC-TEC PWM can only be turned on, but cannot be turned off until the input voltage itself turns off. The picture below is the closest thing I could find for this. The switch turns on "somewhere" in the middle of the AC sine wave, and turns off when the incoming AC sine wave crosses zero.

However, if the incoming power is from a PWM inverter, the waveform crosses zero hundreds of times before the regular AC sine wave normally should have. The result is just a tiny spike of power getting to the motor during each 60 hz cycle.

Last edited by RickChristopherson; 07-06-2011 at 07:23 PM.
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Old 07-06-2011, 10:04 PM
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Default Re: Inverter on ct33

That's really cool, Rick. Thanks so much for posting.

I always wondered what the EC-TEC electronics were doing in my tools - the saw in particular. That must be the "grating" sound you sometimes hear.
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Old 07-06-2011, 11:27 PM
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Default Re: Inverter on ct33

Thanks for all the welcomes.

I found this on amazonamazon a "Sunforce 11260 2500-Watt Pure Sine Wave Inverter"

These have sure come down in price since the last time I looked at them.

The inverter that I have is a modified square wave thats huge compared to the link above.

I think I need one with a 20 amp outlet or a hard wire so I will keep looking. But maybe get the Sunforce for our computers and printers.

So today I went back and used an old shopvac with the ts55 and did not have any problems. Everything ran smooth so I was pretty happy with that.

So at least I got done what I wanted but It sure would have been nice to be able to set up the kapex.
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