run 120v tools off ebike batteries?

veloman

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Is there any problem with series connecting all my batteries to get around 120v and just plug the tool in? Seems a lot cheaper to just buy corded tools. Will 110v under load work okay?
 
No reason that won't work with AC/DC (universal) motors, but true AC motors won't work on DC current. You'd need an inverter of some kind for that.
 
Ditto to what Chalo said...except that you might need closer to 85VDC to equal 120VAC for total actual energy available. (IIRC in my nearly braindead tired state right now, 0.707 would be about the factor to convert one to the other?)

I know my circular saw and all of my AC-powered drills work fine on DC, as do my plug-in weedeaters, my sewing machine, and my original B&D lawnmower did, but I ahvent' tested that with my slightly newer one.

It would *not* work on my lathe, swamp cooler, box fans, cieling fans, washing machine, another pair of lawnmowers (whcih barely work anyway), or a number of other things.
 
amberwolf said:
Ditto to what Chalo said...except that you might need closer to 85VDC to equal 120VAC for total actual energy available.

I'm pretty sure that the nominal voltage for AC power is RMS voltage, meaning 120VAC = 120VDC. The peaks of the cycle are higher.
 
Chalo said:
I'm pretty sure that the nominal voltage for AC power is RMS voltage, meaning 120VAC = 120VDC. The peaks of the cycle are higher.
You're "pretty sure"? I'll excuse that qualifier if it's an understatement, and you are actually absolutely sure. But if you are crafting your answer to leave room for doubt, then that's a cowardly way to correct someone.

The mains V is commonly described using RMS (root mean square) value of the peak V. The 120 V "line" in America is RMS of the peak, which is √2 x 120 . The peak to peak V is twice that.
 
I'm a machinist. I'm never so sure about technical suppositions that I won't measure something when I need to be certain. :)
 
Okay I'm going to try this on a corded weed trimmer. (Black n Decker Grass Hog, maybe 6-10 years old) What's the risk of damaging the trimmer? And how do I figure out the polarity (if there is a risk of wrong way)?
 
veloman said:
Okay I'm going to try this on a corded weed trimmer. (Black n Decker Grass Hog, maybe 6-10 years old) What's the risk of damaging the trimmer? And how do I figure out the polarity (if there is a risk of wrong way)?

If it's an AC/DC motor, the polarity won't matter and it'll fire right up. If it doesn't run right from the outset, it probably won't regardless how you hook it up.
 
veloman said:
And how do I figure out the polarity (if there is a risk of wrong way)?
AC alternates polarities at the hz rate for your local power supply (in the USA, that's usually 60 times per second).

So there is no wrong polarity. ;)

One exception: Some trimmers have a high and low speed, and the low speed often is created by switchign a diode into the circuit to block half the AC. So if you use DC, and have the trimmer on low, it would only operate on one polarity (but it won't be hurt by the other).
 
https://endless-sphere.com/forums/viewtopic.php?f=7&t=75420
 
Thanks for the info.

I'm picking up a free Grass Hog tonight. I feel better about trying it out on that rather than my wife's trimmer.

Would a lower voltage like 50 or 70v hurt the motor, or just run slower?
 
RMS is just the average of an AC sinusodal signal, 0.707 if I remember correctly.
I've looked into this as well, some motors are induction so DC would not work.
I've read also that sometimes you might blow a switch, so starting lower would be best and then move on up.
Best to buy used cheap tools and try it on them before f'ing up your own tools.
 
I used the grass hog gh600 on 52v tonight for my yard. Works okay for light weeds/grass but more voltage is needed. Even adding 3s more seemed like a significant improvement.

I used my old 13s combo of packs on the mower. Pulls 380watts no grass. That's a good deal less power than 14s did (500w). I will want more power for tall grass though. It's not a battery amp issue. Just that the motors torque is at its limit in thick stuff.

Tomorrow I do my first two lawn cuts for money.

I'm now looking into a cheap electric blower. Using the broom is going to get old quick.
 
Well the 65v battery closed the trigger switch on the trimmer. I have to unplug the battery to shut off. Maybe I can replace it inside with something rated for DC current.

The two lawns I did today were a foot tall, not the 3-6" listed on the order. Hopefully they pay me extra as I asked.
 
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