Snowblower use with 7.5Ah and 2.5Ah battery

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I bought the snowblower that comes with 2 5Ah batteries and the 2.5Ah string trimmer. Am considering purchasing the 7.5Ah backpack blower. The snowblower recommends using 5Ah or greater. But I'm wondering what if I buy the backpack blower and pair the 2.5Ah and 7.5Ah batteries together if I run out of juice with the 5Ah snowblower. What do you think?
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snowguy

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Posted 3 years ago

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Blue Angel, Champion

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As far as I know, the snowblower uses both batteries in parallel so they should function roughly the same as the pair of 5Ah batteries.

I'm basing this statement from what Workshop Addict reviewers said when testing the blower: that there's a very small performance hit when using a single 7.5Ah battery vs two 5Ah batteries. If that's the case, adding the 2.5 will likely bridge the gap. My $.02 anyway. :-)
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Blue Angel, Champion

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I should add that Ego recommends using two batteries 4Ah or larger for maximum performance, but that's probably to keep people from expecting too much when using two 2Ah batteries. Once again, my thoughts, not Ego's. :-)
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snowguy

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Thanks Blue Angel! 
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Blue Angel, Champion

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Any time!
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(a)Typical Engineer

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I read through the manual but it does not address the case of using two batteries of different size (it essentially says 2x 4.0AH or greater).  I would be a little concerned with using a 2.5 and 7.5, because depending on how they are wired in parallel, you could end up charging the 2.5 from the 7.5. 

Here are a few thoughts on how that could happen: First the 2.5 is a 1P and the 7.5 is a 3P (three parallel strings of 14S [cells in series]).  If you were to straight wire those in parallel, you'd essentially make a 4P (four parallel strings of 14S), and so far so good. But, by having two batteries, which each have their own BMS (battery management system), we'd have to hear from Ego on how they've engineered it to work.  But they won't be giving away those trade secrets.

Another way they could have engineered it is if the blower has circuitry that prevents a larger or less discharged battery from charging a smaller or more discharged battery.

The safest way to operate the blower would be to have two of the same sized batteries, with the same charge level.  Granted, that over time even two of the same sized batteries will end up a different effective remaining capacity levels, so these concerns might all be a moot point.

Would be great if Ego could officially address the different size battery scenarios in the manual (the current working is not quite explicit enough).
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Blue Angel, Champion

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I think Ego has probably done all the hard work for us on this one.

If I had to guess, the controller would have two inputs and would treat the batteries separately until a load was applied, at which point the voltage drop under load would be equal between the two packs.
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snowguy

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Thanks (a)TypicalEngineer and Blue Angel. 
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Jacob

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Ok so after investigation on how it uses 2 batteries together i have the answer. Its obveyous if your using the snow blower and one battery is dead and the other isn't. Its quite intelligent actually.

It does have a selector between the 2. So only one battery is being used at any time.

The battery light on the snow blower will switch red then green indicating that it is switching power sources

Intelligence as mentioned before.

The blower pulls from the more dead battery when load is not sensed. Basically idling. Why is this smart? Because someone smarter than myself came up with it.

Then as load increases it switches to the other battery. Then balances between the 2 batteries.

Because of this. Using a 7.5 ah and a 2 ah battery will not give you the results you want. It will kill that 2 ah battery very very very very fast. It actually turned red almost immediately.
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Jacob

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Thats cool. But its true :)
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DJDDay

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According to your observation?  Or do you have more detailed info regarding its specs?  :)
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Jacob

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Ugh. Its clearly visible if you would just try it. I Dont have time to keep discussing it dj sorry. Try it with a dead battety and a full one. The light goes from green to red. Back to green / red when you hit a load. Back to red when no load.
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DJDDay

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You misunderstand - I know exactly what you're talking about.  I'm just trying to understand how you would draw that conclusion just because of what you're seeing.  And yes, I see it too on mine, but again... Did you read somewhere that it switches (quickly) between batteries all of the time?  Did an Ego rep tell you this?
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Jacob

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Nope i dont get any inside information :(. Wish i did
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Jennifer VandeWater, Community Manager

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Both batteries should discharge at the same time, regardless of the amperage. The unit is designed to draw power from both batteries at the same time and discharge them at the same rate. Obviously, there will be times when using a 2.0Ah and 7.5Ah that the 2.0Ah will drain first but that's why we suggest using 4.0Ah or higher for optimal performance. Hope this helps explain the functionality.

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