120V dual source--either battery or outlet. More power. + maybe get 112V from 2 56V in series.

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EGO, I challenge you to create 120V battery powered/corded tools. You may know about the GreenWorks 80V Jet blower, you and it inspired me to challenge you to this. 120V battery, but also have the option of using cord to 120V power outlet. How about a stronger jet blower, blower/vac, and backpack blower. How about a backpack for 2 56V packs in series... Or a handheld 120+V blower that is as strong as the strongest backpacks--700-900CFM at 200mph.  I'm talking heavy duty professional stuff for getting the job done fast... EGO Pro 120V or 112V (for 2 or more 56V in series).  
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TheAtomTwister

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Posted 5 years ago

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Blue Angel, Champion

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TAT, interesting idea.  I had contemplated the same a while back.  I have a collection of Makita 18V cordless tools and they have done exactly that - two 18V batteries in series to power 36V tools.

Higher voltage definitely has advantages.  For a given amount of power required, doubling the voltage will halve the current required.  Less current means less heat, smaller gauge wiring, and the potential for higher efficiency.

Having said that, the law of diminishing returns will come into play at some point.  So, for a given amount of power required, at some point it just won't make sense to go with a higher voltage system.  Where that point is I'm not sure, but consider that DeWalt just launched their brand-spanking new line of commercial grade Li-Ion tools and they chose to stick with a 40V platform.  They also did this in a market where much higher voltage platforms are already established.  I would bet they did their homework and figured, for the amount of power their tools would draw, 40V would be enough.

Higher voltage platforms also cost more to produce.

Is 56V better than 40V?  All else equal, yes.  But the advantages are not as great as the voltage difference alone would suggest.  Higher voltage means more cells, and the more cells you have the less stress you put on each individual cell for a given power requirement.

Using 10 4.0V rated cells in series gives you 40V, and 14 cells in series gives you 56V.  If each configuration is made up of 2Ah cells you have a 40V 2Ah pack and a 56V 2Ah pack.  Multiplying the pack voltage by the cell capacity gives you the amount of energy the pack can store in Watt Hours.  In this scenario the 56V pack gives you 112Wh (56 x 2) and the 40V pack gives you 80Wh (40 x 2).  The 56V 2Ah pack has 40% more energy storage and can do 40% more work.  For a given power output each cell is also under 40% less stress, which keeps pack temperatures lower and extends cell life.

Now if we look at a 40V 4Ah pack, things are different.  This pack will use 2 parallel strings of 10 cells in series (2P10S).  For a given power output this pack, even though it has less voltage than the 56V 2Ah pack, will stress its cells less since it's dividing the load over more total cells.  This is a 160Wh pack vs 112Wh, and contains 43% more energy.

Using the DeWalt 40V system as an example, they have a 6Ah battery pack.  This seems VERY impressive on the surface since 6Ah seems high compared to all the other company's 4Ah packs, but it is a 240Wh pack.  Ego's 56V 4Ah pack is 224Wh, almost the equivalent in energy storage as it operates at higher voltage.

Ego's BA2800 56V 5Ah pack, which is the same size and weight as the current 4Ah pack and will be available soon, will be a 280Wh pack.  The BA4200 56V 7.5Ah pack will be 420Wh.

Long story short, higher voltage is better but there is a point of diminishing returns determined by the amount of power required from the tool.  DeWalt and other 40V platforms are likely near that point, and if so Ego is comfortably above it.

In my opinion, the 80V Greenworks tools are positioned that way more as a marketing effort.

Would 112V tools be cool?  Sure they would!  But for the amount of power required to run most yard equipment I'm not sure the costs involved would be justified.
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I think I'm in agreement with you--you are correct across the board.  This is why I almost think that creation of 112V+tools are the job of electrical engineers.  I've just been having problems with finding the right motor for the job.  I wanted to grab a Greenworks blower and use 32 18650 3Ah cells to make a 120V (nominal, 134V max) pack by using their 80V battery as a place to store the cells.  When cells get less expensive, maybe, but until then, 120V+ will just be a little thing for me to work on.  I found 10 18650 4Ah cells for just under $10, so I could theoretically use 32 of 40 of those for $40 to create a simple 120V 4Ah pack.  I just hope that I can find the correct brushless motor for the job.  Hopefully the cells are reliable...   I also found 10 5.8Ah 3.7V cells for $12.44.  I am wondering a bit about the reliability of these cells.  What do you know about UltraFire? (If they work, then I could use 64 to create a 11.6Ah 120V pack, which would have stored in it around 1392Wh on a full charge.  This would be about $100 for cells and housing).  Also, I would increase the voltage and use about the same current for more power. Say for example, increase the power of the blower and make it blow instead of at 92 mph at 125 mph, which would blow 652 CFM.  This would probably require a different motor, however.
(Edited)
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Ultrafire market primarily to the flashlight industry as far as I know. I've seen several technical reviews of their products and, based in those reviews, it seems their cells are quite often over rated.

You also need to be careful when looking at the current draw of the application. The high capacity 18650 cells are fairly low draw devices. The 18650 cells used in power tool batteries are much lower capacity, but can handle extremely high current draw. This is critical in power tool applications.

Until about three years ago, all power tool batteries used 1500 mAh cells (1.5Ah) because those were the only high draw cells available. Then the 2000 mAh high draw cells hit the market and the power tool companies started using those to make 2Ah and 4Ah packs in place of their existing 1.5Ah and 3Ah packs. Then a little over a year ago, high draw 2500 mAh cells hit the market and the 5Ah packs were born. Bosch has announced plans to release a 6Ah 18V pack as soon as the high draw 3000 mAh packs are available for mass production.

So we're still waiting on high draw 3Ah cells, but low draw 18650 cells that exceed 3000 mAh have been around for a long time. Low draw cells are fine for use in low draw devices, but power tools wouldn't perform well with them (too much voltage drop under load) and the cells wouldn't last very long under those high draw conditions.

Now if the pack is large enough (high enough capacity) relative to the power required, the per cell load can be reduced to a safe level. But that would take a lot of cells.

Ego's new 7.5Ah packs will use 3 strings of 14 cells (3P14S), so for a given power output that pack will place 1/3 the draw per cell compared to the 2Ah (or new 2.5Ah) pack which uses 1 string of 14 cells. Same voltage, 1/3 the cells, 1/3 the capacity.

Building packs yourself, you also have to consider pack maintenance. The cells need to stay balanced, so a home built pack will require some TLC to maintain proper performance over time. Also, you need to be VERY careful playing around with high voltage! If you are not experienced or certified to work with high voltage DC packs you should consider the consequences before putting yourself in danger.

Food for thought. When I worked at GM's Engineering Center in Oshawa, the techs who were working on high voltage systems all had to have lengthy specific training on safety and lockout procedures, especially with prototype equipment that was in various states of development. I am not well educated in the differences, but I've been told DC voltage can be extremely hazardous compared to AC.

Building high voltage systems needs to be approached with caution.
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Once again, correct on all counts.  I have thought about the current that would be drawn from cells and I had thought about checking cells individually.  I also did think about dividing current amongst strings of cells, and yes, it does seem like sort of a hefty job.  I'm going to guess that the EGO blower draws 20 amps on turbo?  

If that is the case, then I can in theory create a high voltage pack that would have little current drawn or a multi-string pack if you will (as you stated--many strings in parallel).  I would of course need the proper resistors and the proper insulating equipment and material for such a high voltage system... I would like to learn a bit about these high draw cells that you speak of.  

I had thought about creating a battery box that one would load cells into and then remove cells from to recharge individually.  This would be an inconvenience for most, and is thus not really a marketing idea, but it is nonetheless food for thought.  I do note that if Li-ion cells are too far discharged, they will denature, and this is why batteries need proper maintenance, or at least those that do not evenly discharge do.  

It looks like you have found a happy medium to work with.  I do still keep out there the idea of coupling 56V packs for use with larger motors like for a backpack--use in parallel for extra current or in series for extra voltage.  It seems like the first might be easier because of the risk of overly discharging a battery when using in series... though you guys have the tool shut down when the voltage gets too low, so you already have accounted for that.  It looks to me like I would be up for making a backpack battery that uses many strings of cells... maybe a total of 200 cells, 10 strings of 20 for 74volts nominally and 2 amps per string.  From my experience with using a laser that draws about 2 amps from one of these cells, I know that this would work for a 58Ah 74V pack, and the total cell cost would be about $225.  A 1.4 ohm resistor would make it compatible for 56V, or just use 140 cells.  The only concern that I have with that idea is longevity... the cells would be in parallel, so the voltage of the strings should stay roughly the same... I could put in thermal sensors to make the thing register a heating cell.  I could also make it so cells that go bad can be easily replaced... just fun food for thought... :)

Maybe you can learn more about these cells that I found on eBay.  They are 4.5Ah 26650 cells built for 90 amp discharge current.  I'm not sure that that would be of much use... IMREN makes some 3Ah high drain cells designed for 35A max draw... you may already know about this or something like it, hence "as soon as they're available for mass production".
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Just to be clear, I don't work for Ego, I'm just a geek who hangs out in their forum. :-). Anything I say is only my view, not that of Ego.

The blower will draw about 600W on turbo, about the same as the mower's peak power. On a 14 cell pack nearing the lower end of its charge level that's about 14A, give or take.

Here's a quick read on some popular cells, as well as some good info regarding cell C ratings. This is an e-cigarette page but the info is still valid:

http://www.tasteyourjuice.com/wordpre...
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I think I'm just wanting to see a handheld blower that is as strong as a big backpack blower and that doesn't come with the downsides of backpacks.
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Blue Angel, Champion

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I think most would agree! We'll get there someday... :-)
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I'm curious. Do you know what the maximum current tolerance of ICRs is?  I imagine that it might vary a bit...  their C rating.
(Edited)
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I think you'll find that cells differ greatly in their performance, even within categories. Your best bet is to see if you can find a data sheet for the cells you're interested in using. If you're real lucky you'll find independent tests, though the results of independent tests may be questionable if done by hobbyists with non calibrated equipment and/or questionable processes.
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TK

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Well stated by both parties......Thanks..
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I don't think the circuitry that is built into EGO's packs would allow this.  They actually pair with the equipment they are attached too.  The pack knows if it is a mower, a trimmer, a blower.  I bet messing with them in any other way than intended could pose great risk of frying the circuitry and the battery. 

Cool idea though.