What am I over looking?

[s3w47m88]

I cannot power my DeWalt 15a compound miter saw, even when it's the only thing plugged in, or other large (but consumer grade) power tools and I cannot understand why. I have no problems powering other items like LED strip lights with their respective inverters, charging phones, etc...

I have:
- 2 Renogy 100w panels.
- 1 Renogy 30a MPPT solar charge controller.
- 1 GoWise 12v 3000w/6000w Pure Sine Wave Inverter.
- 4 Trojan T-105 wired in Series and Parallel.
- 1 Extension cord about 25 ft. going straight from the inverter.

 

[solarsimon]

What happens?

 

[Colonel.lp]

The startup current of your mitre saw is probably nearing 5000W, about 3ish times rated load, so I'd check if the inverter is cutting out. If so, it can't handle the load. The surge rating is often fractions of a second.

I don't know the go wise brand, but it looks too small to be a low frequency inverter, which has big transformers to allow handling of surges for longer. The high frequency ones can only handle surges for a short time.

I may be wrong about your situation, but with without more info as to what the inverter is saying, that's what I'd guess.

Also, what size are the cables from the battery to the inverter and how long? If not right they can cause a voltage drop, and the inverter will cut out.

 

[s3w47m88]

The inverter beeps and shuts off.

The saw is 15a at 120v that would only be about 1,800w, and the inverter is rate for 3,000 running 6,000 surge.

 

[John Frum]

The inverter beeps and shuts off.

The saw is 15a at 120v that would only be about 1,800w, and the inverter is rate for 3,000 running 6,000 surge.

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[Colonel.lp]

Basically you probably need a low frequency inverter with an surge current of about 8000 or 9000W.

 

[clarkpeacock]

I cannot power my DeWalt 15a compound miter saw, even when it's the only thing plugged in, or other large (but consumer grade) power tools and I cannot understand why. I have no problems powering other items like LED strip lights with their respective inverters, charging phones, etc...

I have:
- 2 Renogy 100w panels.
- 1 Renogy 30a MPPT solar charge controller.
- 1 GoWise 12v 3000w/6000w Pure Sine Wave Inverter.
- 4 Trojan T-105 wired in Series and Parallel.
- 1 Extension cord about 25 ft. going straight from the inverter.

You could use a soft starter - something like this https://www.motioncontroltips.com/when-do-you-need-a-soft-starter-for-an-ac-motor/

RS PRO Soft Starter, Soft Start, 2.2 kW, 230 V ac, 1 Phase | RS

uk.rs-online.com

But it could end up costing more than upgrading the inverter!

 

[Hedges]

Does the saw have a brush-type motor?
If so, try a dimmer switch (with rating at least 1800W!)
Or whatever dimmer switch you can find, and a toggle switch bypassing it after motor is up to speed.
Cleaner solution is to install a variable-speed switch in the saw, or plug in to a foot control - you would squeeze the trigger switch then use the variable speed pedal.

Alternatively, or if an induction motor, find a smaller motor the inverter is able to start. Get it running, then try to start the saw.
Maybe a big, heavy brush-type motor gradually spun up with dimmer, then fully connected to AC.
I haven't tried/measured what this will do, but idea is it supports line voltage by energy stored in rotating mass.

 

[s3w47m88]

Thanks everyone.

I'd rather upgrade my inverter. Eventually I want my system expanded to power a 3,500 sq. ft. house but for now I'm starting with a Tiny House and equivalent size office structure.

So the idea for a soft start are great ideas but not what I'd like to apply in my situation.

Now, I understand LRA and surge power, but unless my math is wrong (amps x volts = max Watts AKA LRA) I shouldn't be anywhere near my surge power limit with a 6,000 watt surge limit.

And none of my devices that are having trouble have a listed specific LRA rating.

So am I using the wrong math equation or am I overlooking something?

As for low frequency inverters, I am understanding they are more efficient? in absorbing surge, such as the starting of a compound miter saw, but at 6,000w surge in high frequency that seems to me to still be substantially more than is necessary. Most low frequency I'm finding are astronomically more expensive for the same surge power. Which suggests to me they don't require the equivalent surge power because they absorb it so much better. Therefore I buy a lower surge power and yes it will be more than a high frequency but not multiple times the cost.

Is that about right?

 

[upnorthandpersonal]

Now, I understand LRA and surge power, but unless my math is wrong (amps x volts = max Watts AKA LRA) I shouldn't be anywhere near my surge power limit with a 6,000 watt surge limit.

As for low frequency inverters, I am understanding they are more efficient? in absorbing surge, such as the starting of a compound miter saw, but at 6,000w surge in high frequency that seems to me to still be substantially more than is necessary.

A low frequency inverter will be able to provide a surge current for a longer period of time (multiple tens of seconds for some) compared to typically fractions of a second for high frequency ones. Now, with things like motors or other inductive devices you will have an inrush current that is possibly 3 to even 10 times that of the nominal running current. In your calculation you assume 15a at 120v that would only be about 1,800w being your LRA - this is not the case, this is your nominal. Your LRA is probably 3 to 5 times this number, for perhaps a second or more, which your inverter can't deliver.