DIY solar generator to run power tools: start surge miter saw issue

[VincentBuffalo]

I would like to build a solar generator using a 100ah LifePO4 battery and a 2000w invertor (4000w surge). It's a temporary situation as I am building a house and will ultimately be connected to the grid. The 100ah battery + 2000w inverter should be fine for what I need except that I would love to run my miter saw and circular saw with it.

I measured the surge current on my miter saw at 40amps and continuous at 8 amps. The battery can handle 1200w continuous and 2400w surge so with 4800w surge it won't work. I considered the following options:

--> Upgrade to a 3000w (6000w surge) inverter with 2x100ah batteries in parallel --> easy option but too expensive, I might be better off buying a battery miter saw

--> Use the miter saw with a GS10 Soft Starter (plug in). Not sure if it would work but @$130 it's much cheaper

I am a beginner so any comments would be appreciated, thank you!!

 

[sunshine_eggo]

Surge is VERY misleading on some models. If the inverter is a high-frequency type (it's not heavier than crap), the surge is essentially meaningless as the duration is so crazy short, it's not useful in motor starting.

Bigger inverters also tend to have higher self-consumption consuming more of your capacity just by being on.

3000W @ 12V is going to require some pretty beefy wires.

This piece of heavy iron:

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Has a true 3X surge capacity. It's not particularly efficient, and it has a high self-consumption, BUT it can be ordered in 12, 24 and 48V options. If you look around, you can probably find a 2kW version that would also suffice with its 6kW surge.

100Ah is pretty measly, and as you've discovered, it's current limited. You may not be able to rely on the "surge" rating of the battery either.

Note that your 100Ah battery can only power your miter saw for about 45 minutes before it's discharged to near empty.

 

[VincentBuffalo]

Thanks! Very interesting. The inverter is nice but pretty expensive for my small system. I was considering a $300 giandel 2000w inverter…

Any experience with soft start?

The 45mn run time is ok since the saw really doesn’t run much (few seconds per cut) and I can always add another battery later if needed.

Is there any risk to try to run the miter saw with the 2000w inverter and 100ah battery and see what happens or will I damage the inverter/battery?

Thanks again!

 

[BMcL]

For handling surge and giving you plenty of future expandability, go with a SunGold.
They are heavy-duty and can take 3X the rating in surge.
About $2600 on sale

12000W 48V Split Phase Pure Sine Wave Inverter Charger

Sungoldpower 12000W 48V Split Phase Pure Sine Wave Inverter Charger. Pure Sine Wave Inverter charger is a combination of a 48v 240v inverter, AC charger, and Auto-transfer switch into one complete system.It is packed with unique features and it is one of the most advanced 48 volt inverter for...

sungoldpower.com

 

[tealsmoke57]

I have a 10-inch Hitachi miter saw and a Kobalt 10-inch table saw both with 15-amp motors. While I have not measured the surge current I had purchased the 2000 watt giandel inverter and wasn't paying attention and got the modified wave. It would not power up neither saw. I returned it and got the giandel 2200 pure sine wave and they both run fine with that one.

 

[VincentBuffalo]

I have a 10-inch Hitachi miter saw and a Kobalt 10-inch table saw both with 15-amp motors. While I have not measured the surge current I had purchased the 2000 watt giandel inverter and wasn't paying attention and got the modified wave. It would not power up neither saw. I returned it and got the giandel 2200 pure sine wave and they both run fine with that one.

Thanks a lot, I’ll give it a try!

 

[pollenface]

Is there any risk to try to run the miter saw with the 2000w inverter and 100ah battery and see what happens or will I damage the inverter/battery?

Most likely you will exceed the discharge current rating of the BMS or overload the inverter, won't cause permanent damage but your heart will be in your mouth until normality is restored.

Cordless tools are definitely a great alternative in an off grid scenario provided you have a couple batteries to swap between on the go.

 

[VincentBuffalo]

I am trying to do the same thing as you are, so far I got 2 Ampre Time 100AH batteries and a Zantrex Prowatt SW 2000 Inverter. I will be hooking it all up tomorrow and test this weekend. I also purchased the GS10 Soft Start but it will not be here until monday. If this does not work I will try the giandel inverter.

I ended up buying the 24V all in one solar charger PIP2724 (

), I bought it on ebay directly for Taiwan, with shipping it was significantly cheaper than watts247.

I used two 100ah batteries in series and tried with my miter saw, table saw and shop vac. It performed really well. Cables are not heating even when I run power tools for a long time, I added a 120a breaker on the batteries to be safe. I will also connect it to my RV. Overall a great system.

 

[trj]

I was looking at this thread and have a couple of questions.

1. I want to know about how induction surge is handled and covered (by battery or inverter or both) on start up. Is power required covered by the battery or is covered by the capacitors or other equipment within the inverter?

Example; I have a 1HP compressor that runs with a continuous load of the following (120v x 9.8a = 1176w). The induction or startup readings are, (120v x 21.3a = 2556w), so the difference between startup and run is 1380w. So during induction, does the inverter handle the difference to handle the amps/watts within its equipment or capacitors? Does the battery need to only cover the watts needed for run time (at ~1200w) and not induction, or does the battery also have to have enough power to cover the induction load as well (the 2556w)?

2. I saw the Dewalt 1800b powerpack/inverter works with 4 batteries @18v each and is capable of supporting a running load of 1800 watts. So if I understand correctly, the math must work out to be (72v x 25a = 1800w). Are 18v batteries able to support loads up to ~20amps to ~30 amps?

With the power of these power tool batteries (40v, 60v) and the ability to bank them, it would seem that the manufactures are missing a huge market here in not making these a bit more powerful, it looks like Makita has a 1200 backpack and another product, and Dewalt has the one mentioned above. I was looked at the Dewalt to see if I could use it to run a compressor mentioned above (I have the batteries for the Dewalt), but not sure if it can handle the induction surge, if not, I may look at upgrading to some new batteries.

Any thoughts or insights are appreciated.

Thanks
trj

 

[VincentBuffalo]

I am not an electrician so I cannot say what exactly happens with the surge but when I built my 24v system (my last post) the batteries had a surge load rating (2xrunning load =200ah @ 24v = 4800w) and the inverter was also rated to handle 2x the running load of 2.7kw so I wanted to make sure that I was within this range with all my power tools so I measured the surge and was always below 4800w. In practice I built a deck using my compressor, miter saw and circular saw and it worked perfectly. I also ran a microwave and tea kettle in my rv and had plenty of power for a 2 days trip. Total cost was around $1200 for the 24v system and I think that a 12v system wouldn’t be able to handle it. I am also surprised that tool makers are not coming with a comparable system.

 

[trj]

@VincentBuffalo Thanks for the reply. I appreciate your original post, system, and reply and information. That looks like a great setup and I like that controller too, and I like the idea of doing something similar, but with lighter weight batteries.

If possible, I want to see if I could keep weight down to keep it portable, which is why I was considering banking 4 smaller tool batteries, a similar idea to the Dewalt 1800B system (same idea, but upsizing the batteries from 18v to 60v), but I'm unsure what the max amps an either an 18v or 60v battery can handle (4 batteries @ 60v x ~20a = 4800w just like you did) without frying them out upon induction surge.

The idea was I could build this and use it to power tools (hot swapping batteries for short periods as needed) yet use it for some other loads.

Thanks!
trj

 

[VincentBuffalo]

@VincentBuffalo Thanks for the reply. I appreciate your original post, system, and reply and information. That looks like a great setup and I like that controller too, and I like the idea of doing something similar, but with lighter weight batteries.

If possible, I want to see if I could keep weight down to keep it portable, which is why I was considering banking 4 smaller tool batteries, a similar idea to the Dewalt 1800B system (same idea, but upsizing the batteries from 18v to 60v), but I'm unsure what the max amps an either an 18v or 60v battery can handle (4 batteries @ 60v x ~20a = 4800w just like you did) without frying them out upon induction surge.

The idea was I could build this and use it to power tools (hot swapping batteries for short periods as needed) yet use it for some other loads.

Thanks!
trj

Good idea, I’d love to see pictures if you end up building it. I carry mine in a large tote so it’s kind of portable but I agree, it’s on the heavier side! Good luck

 

[12VoltInstalls]

got the giandel 2200 pure sine wave and they both run fine with that one.

Some giandel models claim a soft-start feature built in. My 1200W does.

 

[trj]

Bumping this to see if anyone has an answer.

I want to know about how induction surge is handled and covered (by battery or inverter or both) on start up. Is power required covered by the battery or is covered by the capacitors or other equipment within the inverter? Does a battery have to be powerful enough to be able to cover the surge watts or will the inverter take care of it?

 

[12VoltInstalls]

or is covered by the capacitors or other equipment within the inverter?

One thing I wondered about and actually learned was true on this site is that electronic/capacitor inverters - even decent quality inverters- basically only deliver milliseconds of ‘surge’ capacity. Transformer (coil) low frequency inverters actually output over their ratings for a short time like 30 seconds or 2 minutes.

Basically the high frequency inverters (inexpensive ones) have no effective surge as it’s essentially a capacitor dump is my understanding.

Smarter people than me will have the science and terminology correct.

All I know is the inexpensive Giandel 1200W ramps up slowly when I turn on my shop vac instead of merely faulting out the inverter or stalling the shop vac. Giandel was a good pick on the low priced shelf

 

[trj]

@12VoltInstalls Thank you very much for the reply and I appreciate that information, very helpful. So it sounds to me that when sourcing a battery and inverter for a project, the battery must have enough capacity to cover continuous wattage requirements and the inverter needs to be capable to cover the surge wattage requirements. That is great info you provided on the transformer (coil) low frequency inverters on how they cover the surge for a longer duration, I will definitely include that in my search. Thank you for your help!

 

[12VoltInstalls]

have a 1HP compressor that runs with a continuous load of the following (120v x 9.8a = 1176w). The induction or startup readings are, (120v x 21.3a = 2556w), so the difference between startup and run is 1380w

Thank you for your help

No problem but I think I got confused with OP for a bit.

In your situation with a 1HP compressor a low frequency inverter is best. A good high frequency inverter can work but forget its surge rating as it means nothing in practical terms.
In overall answer, per Wh tool batteries are not cost effective to gang for big loads imho. With sufficient solar and even lead acid batteries as a buffer (LiFePo a better choice at that level) you can run your saws and compressor but maybe not all at once.

Are you trying to do solar for location purposes? To be “green?” To save money?
You won’t probably save money with solar; the green component is debatable and or subjective. If no grid available for a thousand miles then ok. But you need more than tool paks. Sometimes the “more expensive way” ‘costs’ less and is way less of a pain in the knickers.

 

[trj]

@12VoltInstalls I understand what you are saying.

Are you trying to do solar for location purposes? To be “green?” To save money?

For this purpose, I want to learn what was possible practically and theoretically running a 1HP 120V compressor off the truck using a small and portable system, and what could be done (from small size on up) with the equipment I have. I already have and carry on the truck the Ryobi and Dewalt batteries. I know that I could get a 12v compressor, but I see most of them are limited with the tools you can use, so for this consideration I was going with the 120v compressor to see what it could support in a sprint type of job.

I was curious about what was possible using higher voltage batteries (18v, 20v, 40v) and if they are capable of when banked together instead of creating a new system and hauling 2 larger batteries around (though this seems the route I may go).

There are products such as the Ryobi 40V 1800w/3000 Peak (which uses 40v 5ah batteries and costs ~$700 wow!) and the Dewalt DCB1800B 1800w continuous/3600w Peak (which uses 20v batteries @~$450 - $530 whoa!)) are possible, but, in some ways, each has limitations. The Dewalt does more with less in terms of offering a better peak surge with 600 more watts than the Ryobi, and the Ryobi offers the pure sine wave which the Dewalt does not. I do think the Dewalt is outdated, and I don't see it in big-box stores now so they may be dropping it or updating it to compete with Ryobi.

I don't think either of them offer built-in DC charging which seems lame.

 

[efficientPV]

I had a cute little ONAN 400W gas generator which was light and portable. With my miter saw it would kill the generator. I used a buck transformer to lower the voltage about 24V and boost the current. I had to bump the saw initially to start and after that it would run fine. Something that might be considered.

 

[trj]

@efficientPV Thanks. I've never used a buck transformer and I'm not familiar with it's application, if I lower the voltage, can lower voltage input affect the motor the motor, in a bad way? I just started to look at some youtube videos on this with your suggestions. Thank you much!