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2019 Focus Jam2 6.8 Plus Review
- Thread starter Rob Rides EMTB
- Start date
nickB
Active member
Nice review. I was going to buy a Jam2 (2018) but to get the reach I liked I would need an Extra Large and, as mentioned, that high top tube just felt a bit...high!
I also didn't really like the Derailleur style mode shifters.
Once I tried the large Levo it just felt more comfortable.
For some reason Focus are not selling Ebikes in the USA in 2019!
I also didn't really like the Derailleur style mode shifters.
Once I tried the large Levo it just felt more comfortable.
For some reason Focus are not selling Ebikes in the USA in 2019!
steve_sordy
Wedding Crasher
Interesting comment, anyone know why?
edit: I mean why they are not selling in the USA, not why it is interesting!
Nice review, but being an engineer I feel compelled to point out few false statement in EMTB Tech section:
"
"A 378Wh battery doesn’t just have less capacity than the 500Wh version, it’s also less capable at delivering current. "
Battery capacity (in Wh) has no impact on current delivery capabilities whatsoever. The current is drawn from battery and depends on the electrical load (impedance). If there is no load (open circuit, infinite impedance) there is zero current. If there is a short circuit, the current is theoretically infinite. In real life the high current surge will thermally destroy whatever caused the short circuit (any fuse is based on this principle). Any size load in between these two extremes will draw the current in accordance with The First Ohm Law. The only difference between these two batteries is the amount of time the current can be drawn for. Both of them are equally capable at delivering current given the equal load.
"An ebike battery consists of several 3.6V battery cells. By putting 10 cells in series we get 36V. But 10 cells in series is not any better at delivering current than a single cell."
Cells need to wired in parallell to be able to deliver enough current."
Considering a single cell is 3.6V and whole battery requirement is to operate at 36V, the 10 single cells must be connected in series. Cells don't need to be wired in parallel to be able to deliver enough current, they are wired in parallel because current drawn from each cell in 4 parallel cell combo is one quarter of total current , therefore that parallel cell combo will have (theoretically) 4 times the capacity (Wh) compared to single cell.
It maybe as clear as mud for some, but it may help someone not to make a decision to ditch Focus because that someone may have read a misleading "technical" explanation that it has a battery that is inferior to any other batteries, will deliver less power etc. This battery is perfectly OK, it is smaller and lighter, but it will not make the same distance as 500Wh one with the same motor, rider and ride profile. That's it.
"
"A 378Wh battery doesn’t just have less capacity than the 500Wh version, it’s also less capable at delivering current. "
Battery capacity (in Wh) has no impact on current delivery capabilities whatsoever. The current is drawn from battery and depends on the electrical load (impedance). If there is no load (open circuit, infinite impedance) there is zero current. If there is a short circuit, the current is theoretically infinite. In real life the high current surge will thermally destroy whatever caused the short circuit (any fuse is based on this principle). Any size load in between these two extremes will draw the current in accordance with The First Ohm Law. The only difference between these two batteries is the amount of time the current can be drawn for. Both of them are equally capable at delivering current given the equal load.
"An ebike battery consists of several 3.6V battery cells. By putting 10 cells in series we get 36V. But 10 cells in series is not any better at delivering current than a single cell."
Cells need to wired in parallell to be able to deliver enough current."
Considering a single cell is 3.6V and whole battery requirement is to operate at 36V, the 10 single cells must be connected in series. Cells don't need to be wired in parallel to be able to deliver enough current, they are wired in parallel because current drawn from each cell in 4 parallel cell combo is one quarter of total current , therefore that parallel cell combo will have (theoretically) 4 times the capacity (Wh) compared to single cell.
It maybe as clear as mud for some, but it may help someone not to make a decision to ditch Focus because that someone may have read a misleading "technical" explanation that it has a battery that is inferior to any other batteries, will deliver less power etc. This battery is perfectly OK, it is smaller and lighter, but it will not make the same distance as 500Wh one with the same motor, rider and ride profile. That's it.
Yeah, 10 cells must be wired in series to acheive 36V. So if you want to alter the size of a battery, you can add or remove 10 and 10 cells.
Wiring cells in parallell will increase the current rating. It's difficult to decide how technical I should go while still making it easy to understand. I could have been clearer about the 378Wh vs 500Wh. I'm talking about the Focus battery vs the Shimano/Bosch batteries. A 40 cell battery will be better at delivering current than a 30 cell battery when both are using the same cells. Let's assume they're both using 2C cells. The 10.4Ah Focus battery can deliver 20.8A. The 14Ah Shimano battery can deliver 28A. The point of that text was that even though current rating is lower, the battery is still "powerful" enough to do the job.
Not any huge errors as far as I can see, but I might be misunderstanding what you're saying?
Wiring cells in parallell will increase the current rating. It's difficult to decide how technical I should go while still making it easy to understand. I could have been clearer about the 378Wh vs 500Wh. I'm talking about the Focus battery vs the Shimano/Bosch batteries. A 40 cell battery will be better at delivering current than a 30 cell battery when both are using the same cells. Let's assume they're both using 2C cells. The 10.4Ah Focus battery can deliver 20.8A. The 14Ah Shimano battery can deliver 28A. The point of that text was that even though current rating is lower, the battery is still "powerful" enough to do the job.
Not any huge errors as far as I can see, but I might be misunderstanding what you're saying?
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highpeakrider
E*POWAH Master
“If you’re riding in the winter and are experiencing temperatures below 0°C, you will need to store the bike indoors. If the battery gets cold enough it cannot be recharged. “
Focus simply state the battery has a two year warranty, technically nowhere do they state the bike has to be kept indoors if below 0 degrees, mine isn’t it’s stored in the garage.
Where do Focus make this a technical requirement?
Focus simply state the battery has a two year warranty, technically nowhere do they state the bike has to be kept indoors if below 0 degrees, mine isn’t it’s stored in the garage.
Where do Focus make this a technical requirement?
Many battery users are unaware that consumer-grade lithium-ion batteries cannot be charged below 0°C (32°F).
If you're not riding during the winter, and therefore not recharging it, storing it outside usually isn't a problem. Also it's an advantage if the battery temperature is about +20°C when you start riding.
If you're not riding during the winter, and therefore not recharging it, storing it outside usually isn't a problem. Also it's an advantage if the battery temperature is about +20°C when you start riding.
All Mountain Coaching
E*POWAH Elite
Nice little review. I agree with your comments about needing use less "muscle" to maneuver the bike around. It is definitely on of the more/most nimble emtbs of the current crop.
The non-removable battery is a deal breaker for most though.
The non-removable battery is a deal breaker for most though.
@knut7 In all respect, this statement is not correct:
"The 10.4Ah Focus battery can deliver 20.8A. The 14Ah Shimano battery can deliver 28A. "
The 10.4Ah Focus battery can deliver any amps you want it to deliver. It will happily deliver 28A (and more) if you load the battery more. What 10.4Ah value means it can deliver 10.4 amps at nominal voltage (36V) for 1 hour. After 1 hour it is completely discharged. But it also can deliver 104 amps for six minutes before it will be empty. Shimano at 104 amps draw will last a little longer maybe 8 minutes. Both of them will be quite hot - there's ~3.6 kW of energy in such electrical circuit to be dissipated somewhere.
The actual time in real life will be less due to battery chemistry, but there's no need to complicate it (ref. Peukert's Law).
Both batteries are equally capable of delivering current, they have different energy capacity, so the part after comma of the statement in original review: A 378Wh battery doesn’t just have less capacity than the 500Wh version, it’s also less capable at delivering current. is not true.
"The 10.4Ah Focus battery can deliver 20.8A. The 14Ah Shimano battery can deliver 28A. "
The 10.4Ah Focus battery can deliver any amps you want it to deliver. It will happily deliver 28A (and more) if you load the battery more. What 10.4Ah value means it can deliver 10.4 amps at nominal voltage (36V) for 1 hour. After 1 hour it is completely discharged. But it also can deliver 104 amps for six minutes before it will be empty. Shimano at 104 amps draw will last a little longer maybe 8 minutes. Both of them will be quite hot - there's ~3.6 kW of energy in such electrical circuit to be dissipated somewhere.
The actual time in real life will be less due to battery chemistry, but there's no need to complicate it (ref. Peukert's Law).
Both batteries are equally capable of delivering current, they have different energy capacity, so the part after comma of the statement in original review: A 378Wh battery doesn’t just have less capacity than the 500Wh version, it’s also less capable at delivering current. is not true.
The first statement you are quoting is based on this
"The C rating of a battery (or cell) is used to indicate the continuous current draw (amps) the cell will support. By multiplying the C rating times the cell capacity in milliamperehours (mAh), the continuous current in milliamperes (mA) of a cell is easily calculated. Example - For a 2000 mAh battery with a 15C rating, the continuous current that may be drawn out of the battery is 2000 mAh x 15 = 30000 mA, or 30 Amps (A)." Battery C Rating
Translating that to a 10.4Ah, 2C battery: 10.4Ah * 2 = 20.8A. The continous current that may be drawn is 20.8A. For a 14Ah, 2C battery, the continous current that may be drawn is 28A.
You say a 378Wh can deliver 104A for 6 minutes. Are you saying there is no limit to how fast current can be drawn from these li-ion cells? I think the 3500mAh 18650 cells used today are capable of more than 2C btw.
I agree with some of what you're saying. By trying to keep things short, some of it is unprecise.
"The C rating of a battery (or cell) is used to indicate the continuous current draw (amps) the cell will support. By multiplying the C rating times the cell capacity in milliamperehours (mAh), the continuous current in milliamperes (mA) of a cell is easily calculated. Example - For a 2000 mAh battery with a 15C rating, the continuous current that may be drawn out of the battery is 2000 mAh x 15 = 30000 mA, or 30 Amps (A)." Battery C Rating
Translating that to a 10.4Ah, 2C battery: 10.4Ah * 2 = 20.8A. The continous current that may be drawn is 20.8A. For a 14Ah, 2C battery, the continous current that may be drawn is 28A.
You say a 378Wh can deliver 104A for 6 minutes. Are you saying there is no limit to how fast current can be drawn from these li-ion cells? I think the 3500mAh 18650 cells used today are capable of more than 2C btw.
I agree with some of what you're saying. By trying to keep things short, some of it is unprecise.
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Macone
E*POWAH Master
its been interesting watching this debate but I don't really see the relevance of the scientific "Maximums" being quoted. in essence, these same batteries can be used to power some of the bigger 1000w motors available or power the 250w motors de-restricted. This would leave me to believe that the software currently being used to power our 250w motors (nominal) is more than capable of drawing the same current and voltage from the 500wh battery or the 378wh battery to allow for the 250w nominal plus the necessary peaks for "Boost" mode e.t.c. as these should not reach maximum potential difference(voltage) or current flow from either battery until they are nearly run flat. obviously on the bigger motors or de-restricted, things would change considerably. This would also apply to some of the new 700wh batteries that are beginning to appear from for example Specialized. these bikes still run the same 250w nominal motor and run at the same power due to software.
It seems this discussion stopped. Just to make things clear. What I'm saying in the "EMTB Tech" section is correct.
Sure, in theory you can pull 100A from a 10Ah battery in 6 minutes, or 5A for 2 hours. But there are other factors to consider. The ebike batteries I'm talking about here are li-ion cells, they have a voltage of 3,6V and mostly a capacity of 3500mAh (3,5Ah), they can deliver up to 10A current continously. The C-rating is somewhere around 2-2.8 (10A/3,5Ah=2,85). Most likely the BMS won't let us pull 10A from the cell, to get more charge cycles from it.
The focus 378Wh battery has 3 cells in parallell and should be able to output more than 20A. That should be enough for a motor pulling 600W, it requires about 17A. (600W=36V*I -> I=16.7A). But what happens when the state of charge is low? (600W=33V*I) The battery needs to deliver 18.2A. And what happens when it's cold outside? The current discharge capacity decreases due to increased internal resistance in the cells.
That's the whole point of the EMTB Tech in this article. Are we getting to a point where the motor draws more than the smaller battery with lower current output can deliver? And the answer according to Focus is "No". I had a few rides in -7*C and had no trouble, so it seems Focus is right.
Sure, in theory you can pull 100A from a 10Ah battery in 6 minutes, or 5A for 2 hours. But there are other factors to consider. The ebike batteries I'm talking about here are li-ion cells, they have a voltage of 3,6V and mostly a capacity of 3500mAh (3,5Ah), they can deliver up to 10A current continously. The C-rating is somewhere around 2-2.8 (10A/3,5Ah=2,85). Most likely the BMS won't let us pull 10A from the cell, to get more charge cycles from it.
The focus 378Wh battery has 3 cells in parallell and should be able to output more than 20A. That should be enough for a motor pulling 600W, it requires about 17A. (600W=36V*I -> I=16.7A). But what happens when the state of charge is low? (600W=33V*I) The battery needs to deliver 18.2A. And what happens when it's cold outside? The current discharge capacity decreases due to increased internal resistance in the cells.
That's the whole point of the EMTB Tech in this article. Are we getting to a point where the motor draws more than the smaller battery with lower current output can deliver? And the answer according to Focus is "No". I had a few rides in -7*C and had no trouble, so it seems Focus is right.
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steve_sordy
Wedding Crasher
That is comforting to know. My Focus is yet to be delivered. During my search for the right emtb for me, this sort of stuff was not a factor, at all!
The basic design is now in its third year, so any material issues would be public knowledge by now. We've spoken to many Focus dealers over the past six months and no one has even mentioned anything to do with the batteries, other than to point out that they are bespoke to the design. The best of them (Cycle-Elec in Saintes) had nothing but good things to say about Focus, despite being a multi-brand dealer (and no, we weren't there to buy a bike!), hence why we keep buying them!
steve_sordy
Wedding Crasher
Phew, all good news!
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