Observed capacity from Ryobi 40V battery

[meep]

I've been rather suspicious that the ryobi battery (40V, 4AH) which came with the powerhead for my hedge trimmer is not accurately rated. I finally have some clumsy observations.

Yesterday, I used the 40V battery with its digital sine wave inverter (ryobi) to charge a deep cycle battery with a digital, computerized charger. I did this twice. The computerized charger was set to a 5A limit (at 12V) and it captures total mAH delivered into the battery under charge.

[40V batt]->[ryobi sine inverter]->[digital charger]->[12V deep cycle batt]

In both cycles, the charger came up to about 14.9V and began tapering the amperage down to not exceed 15V. So I'll use an average of 14.5V (between 12.5 where it started with the highest current and then 14.9 where it spent a little more time tapering down). This average will throw the calcs off a little, but not so much as to discount my observations.

Charge 1: 4800 mAH at 14.5V = 69.6 WH*
Charge 2: 5400 maH at 14.5V = 78.3WH

*I cut charge 1 a little short, stopping the charger when the inverter started to flash warning, but before the 40V battery actually tapped out. So we'll got with #2.

Assuming that the 40V battery is a 40V battery, and not a 36 (?), it's math looks like this:
78.3WH/40=1.95AH

Ouch.

Maybe it's really a 36 volt cell.

78.3/36=2.175AH

That's still an ouch.

Assuming that there is 10% loss (pretty high) in the inverter, and an additional 10% loss in the charger, for a total of 20% loss, the battery could get a little love here.

1.95/.8=2.43 at 40V
or
2.2/.8=2.75AH at 36V

So, best case, the battery is providing 68% of its rated capacity if it's really a 36V cell, or 60.8% it's rated capacity if it's a 40V.

(note, it's been used probably 10 times now, 2 full discharges and the rest are partial, maybe 50%-75% SOC).

Booooo.

-m

 

[Dave9]

It is a 36V battery, any 20V is really 18V and 40V really 36V and so on.

Inverters aren't always 90% efficient, some inexpensive modified since wave type are closer to 80%.

Where to account for the rest of your losses, some of it could be the drain rate, see if you can measure the current draw from the battery, then find out which cells Ryobi uses in those, and consult that cell manufacturer datasheet for rated capacity at that current.

There's nothing all that special or different about Ryobi's packs vs other manufacturers, in the end it's just a series of cells, probably a parallel series of 18650 to reach 4Ah rating in this case. On the other hand there is some small % chance that the pack has a defect, just as there is that chance with any brand.

I'd do a different test that removes the inefficiencies, like directly measure current with a DC clamp meter running a tool with a brushed motor, or any other fixed value resistive load you rig up. I'd prefer the fixed value and set it to the drain rate that the cell manufacturer datasheet states is the rate per the capacity.

 

[zzyzzx]

I'm adding your story to my long list of reasons to only buy corded items.

 

[wpod]

Electrical components had a manufacturing tolerances.

 

[meep]

It is a 36V battery, any 20V is really 18V and 40V really 36V and so on.

Inverters aren't always 90% efficient, some inexpensive modified since wave type are closer to 80%.

Where to account for the rest of your losses, some of it could be the drain rate, see if you can measure the current draw from the battery, then find out which cells Ryobi uses in those, and consult that cell manufacturer datasheet for rated capacity at that current.

There's nothing all that special or different about Ryobi's packs vs other manufacturers, in the end it's just a series of cells, probably a parallel series of 18650 to reach 4Ah rating in this case. On the other hand there is some small % chance that the pack has a defect, just as there is that chance with any brand.

I'd do a different test that removes the inefficiencies, like directly measure current with a DC clamp meter running a tool with a brushed motor, or any other fixed value resistive load you rig up. I'd prefer the fixed value and set it to the drain rate that the cell manufacturer datasheet states is the rate per the capacity.

Right on all accounts. The drain rate for most of the time should have been between 0.7 and 2 amps on the 40v side, which should be low enough to not incur a lot of waste innthe cells, just as a seat-of-pants measure. But you are certainly correct, a known load with a meter would be more accurate.

 

[Cujet]

I'm not at all surprised to see "optimistic" specifications. They have to be competitive with the higher end products.

I have a EGO blower with it's 56V battery. Despite it's robust specifications, it can only blow leaves for 12-13 minutes. Not nearly enough to clear my small PA yard of fall leaves. The initial performance is good, but like all things electric, it loses some power as the battery drains, and then dies suddenly, without warning. I really enjoy waiting nearly 2 hours for the battery to recharge. As you might expect, it's now been re-tasked with hangar cleaning, instead of yard work.

My 25 year old Echo 210 21cc blower is just as powerful as the EGO, and will run for more 45 minutes on a tank. It will complete the job on less than a tank of fuel.

 

[thastinger]

37V most likely. Full charge of an 18650 LiFePo4 cell is 3.7VDC. Assuming they build the pack in a 10S configuration. There is no technical reason they couldn't do 11S though, they just usually stick to even number configurations when constructing batteries from cells.

 

[Ursatdx]

Jersey wants to ban gas blowers.
My RedMax 8500 is a gas eating monster.
I have an acre with many, many Oaks.
Guess I'll fire up the Genny to power the electric.

 

[Dave9]

37V most likely. Full charge of an 18650 LiFePo4 cell is 3.7VDC.

No consumer grade tool I'm aware of, uses LiFePO4... but if they did, the nominal voltage of those is 3.2V and nominal voltage is how packs "used" to be rated, similar to how it all started with NiCd powered tools, where the nominal voltage of NiCd cells is 1.2V so there were 15 in series for an 18V NiCd tool battery. Well, even that is skipping the lower-than-18V cordless tools before the 18V era but they were also calculated based on # of nominal 1.2V cells.

With the newer generation/screwy rating system, a 10S2P "so called" 40V/4Ah battery pack of Li-Ion would have a full charge voltage near 42V (4.2V/cell), but still a nominal (average) voltage of 36V.

 

[UncleDave]

The battery blowers just aren't there like trimmers and hedgers are.

Sure they are fine for a porch or garage - but an acre + they aren't getting it done.

Put in an order for the makita 75CC backpack unit - Im fixing this problem once and for all - in before the ban.

 

[Owen Lucas]

Jersey wants to ban gas blowers.
My RedMax 8500 is a gas eating monster.
I have an acre with many, many Oaks.
Guess I'll fire up the Genny to power the electric.

Would this be in the burbs only for noise reasons or are they worried about pollution? When will this madness stop?! /s

 

[Ursatdx]

Murphy just does what California does.

They should ban his teeth.

California Enacts Ban on Gas-Powered Lawn Mowers, Leaf Blowers

Hate those gas-powered leaf blowers? N.J. may be banning them.

The first measure, S4273, would prohibit the sale of gas-powered leaf blowers within a year of the bill becoming law and ban their use entirely after four years. Introduced by Sen. Bob Smith, D-Middlesex, chair of the Senate Environment and Energy Committee, the bill would levy fines of up to $1,000 for each offense.

 

[Rand]

The battery blowers just aren't there like trimmers and hedgers are.

Sure they are fine for a porch or garage - but an acre + they aren't getting it done.

Put in an order for the makita 75CC backpack unit - Im fixing this problem once and for all - in before the ban.

4stroke motor let us know how you like it.

I really like my echo.. Also be interested to know where they measure the cfm and mph at.

many are cheaty and measure it in the housing.. others measure it at the end of pipe
I dont care as long as they list where its measured at.

Only thing about my echo is the elbow is not very flexible and its LOUD.
but 1071@212mph moves the leaves.. there is no pileup where you struggle with wet leaves.. they just move.

 

[meep]

The battery blowers just aren't there like trimmers and hedgers are.

Sure they are fine for a porch or garage - but an acre + they aren't getting it done.

Put in an order for the makita 75CC backpack unit - Im fixing this problem once and for all - in before the ban.

I have the makita. It’s powered by a honda and it has grunt. It’s well built, and I prefer 4 cycle tools. it took me a while to get used to the makita - the CG is like a foot behind you, so it won’t stay flat to your back regardless how you adjust the straps, and until getting used to it, it’s rather awkward/uncomfortable. It might be better if some malleable aluminum was extended below the frame to press against the butt and not try to roll off your back so much.

my prior toro backpack 4 stroke was far more comfortable. But it (a) fell apart (b) required trimming the nozzle back to get a better flow/pressure balance and (c) wasn’t as powerful.

 

[UncleDave]

I have the makita. It’s powered by a honda and it has grunt. It’s well built, and I prefer 4 cycle tools. it took me a while to get used to the makita - the CG is like a foot behind you, so it won’t stay flat to your back regardless how you adjust the straps, and until getting used to it, it’s rather awkward/uncomfortable. It might be better if some malleable aluminum was extended below the frame to press against the butt and not try to roll off your back so much.

my prior toro backpack 4 stroke was far more comfortable. But it (a) fell apart (b) required trimming the nozzle back to get a better flow/pressure balance and (c) wasn’t as powerful.

Good and bad to know.

I totally appreciate all feed back thanks!

 

[Dave9]

4stroke motor let us know how you like it.

I really like my echo.. Also be interested to know where they measure the cfm and mph at.

many are cheaty and measure it in the housing.. others measure it at the end of pipe
I dont care as long as they list where its measured at.

I agree they need some standardization but wouldn't call it cheating. Measured in the housing you would have a higher CFM number without a concentrator nozzle but lower airspeed. Most important thing is that they list both and in the case of cordless battery powered, how long it can do that at full throttle. Instead they tell you the max performance with a full battery pack, though this matters less with a brushless blower than brushed.

I'm among those very displeased at cordless blower performance, but really I mean battery prices since I wouldn't mind a battery that weighs a couple lbs more. It just takes a lot of battery to move enough air to get much done.

I get about 10 minutes runtime with one that's equivalent to a handheld 2 stroke's performance (and that's from NEW, not after the battery ages/degrades), and a bigger battery to get a mere 20 minutes when new, costs about $250. End result is I just mow/mulch more which is just as loud, but possibly pollutes less from not being a 2 cycle, and definitely adds less to landfills by not throwing away perfectly good leaf mulch. Soil is high clay here, I'll take all the leaf mulch I can get.

 

[Dave9]

Right on all accounts. The drain rate for most of the time should have been between 0.7 and 2 amps on the 40v side, which should be low enough to not incur a lot of waste innthe cells, just as a seat-of-pants measure. But you are certainly correct, a known load with a meter would be more accurate.

We seem to still have some disagreements about the losses.

First, it's a 36V nominal pack, that is the average voltage before cell manufacturer recommended cutoff voltage limit. Did Ryobi follow that? I do not know but you can run it down to that limit where the BMS circuit disconnects/shuts-down, then measure for the lowest voltage cell in the pack to see what the cutoff voltage was. It's entirely possible you simply have a single bad cell in the pack and the BMS shuts down early due to it but regardless, I don't know where you are getting this "between 0.7 and 2 amps".

If you had 36V (average) into an 80% efficient inverter to get to 110V, then let's say an 85% efficient charger to get 78.3WH output to a battery, the math I'm doing is:

78.3WH/.85 = 92WH into the charger.

If inverter is 80% efficient that's 92WH/.8 = 115WH into the inverter.

If battery is 36V nominal, that's 115WH/36V = 3.2A

It still seems short of expectations since the cells should be more than capable of a 3.2A drain rate without substantial capacity derating, for any cell reasonably chosen for a tool battery at least, but not as low as the drain rate you listed which seems impossible, or did I do the math wrong?

I've reverting back to the idea that you need a fixed load, to measure input current, output current, and voltage at both ends simultaneously. For one thing it is fairly unlikely (impossible) that the charger managed to maintain a steady 5400 mAh at 14.5V the whole time, that it had to either vary the current or the voltage to keep the other value regulated, as the battery charge voltage continued to rise. That variation may not be significant if the battery was not deep discharged, but it is yet another few % one way or the other... it all adds up.

 

[meep]

this will help - no I’m not being thoroughly scientific and don’t intend to, just passing a rough order magnitude. The charger displayed a total of 5400mah delivered during the full duration of the cycle. it’s a counter…. Starts at 0000 and goes up. so I know that the charger saw a total of 5400 mah passed. I rough-ordered the average voltage to get an average figure - since it pushed 5A full tilt when the voltage started at 12.5, then as the voltage reached 14.9 then starts reducing the current to keep it at 14.9, until it finally reaches 14.99 at a low low current and turns off. In this case, the “40”v cell was depleted before it reached an endpoint.

so yeah, I’m not shooting for perfect numbers, that’s not my point or intention. My point is to throw one data point out on the web, that others will surely build upon. It is a better data point than say, “I don’t think it’s full capacity cuz my buddy’s does better…” or something purely subjective like that.

 

[repairman54]

Murphy just does what California does.

They should ban his teeth.

California Enacts Ban on Gas-Powered Lawn Mowers, Leaf Blowers

Hate those gas-powered leaf blowers? N.J. may be banning them.

The first measure, S4273, would prohibit the sale of gas-powered leaf blowers within a year of the bill becoming law and ban their use entirely after four years. Introduced by Sen. Bob Smith, D-Middlesex, chair of the Senate Environment and Energy Committee, the bill would levy fines of up to $1,000 for each offense.

I guess we'll have to make Sussex County a 2-stroke sanctuary county then so we can blow leaves and cut firewood. We have the votes here.

 

[thastinger]

No consumer grade tool I'm aware of, uses LiFePO4... but if they did, the nominal voltage of those is 3.2V and nominal voltage is how packs "used" to be rated, similar to how it all started with NiCd powered tools, where the nominal voltage of NiCd cells is 1.2V so there were 15 in series for an 18V NiCd tool battery. Well, even that is skipping the lower-than-18V cordless tools before the 18V era but they were also calculated based on # of nominal 1.2V cells.

With the newer generation/screwy rating system, a 10S2P "so called" 40V/4Ah battery pack of Li-Ion would have a full charge voltage near 42V (4.2V/cell), but still a nominal (average) voltage of 36V.

Sure they do. You can get the old A123 made 26650 LiFePo4 cells from the old large 18V Dewalt batteries. 18650 cells are everywhere, like in Tesla power walls. The newer flat style black and decker/dewalt etc batteries are made from flat cells but it is all LiFePo4 chemistry.