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12V accessory port adapters and 'fast charging' - an overview

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Someone here said that you can't fast charge a mobile phone from the 12V accessory port on the dashboard via a USB adapter, and that you have to run a wire directly from the battery to do this. I found this statement somewhat odd.

In this post I attempt to deconstruct this statement and investigate its accuracy.

TLDR: the statement is both incorrect and correct. It's complicated, just like the USB standard.

The Yamaha Tracer and Niken (and many other motorcycles) offer a 12V accessory port. This used to be called the 'cigarette lighter plug'. It is a switched circuit that is fused to 2 amps (2A) at 12 volts (12V). This indicates a maximum power output of 24 watts (24W), when you apply Ohm's law:



Power (watts) = Voltage (volts) * Current (amps)

'Switched circuit' refers to how it's linked to the bike's ignition. It's off when the bike is off, and on when the bike is on.

USB power
This gets very complicated very quickly - but at its most basic level, USB power is delivered at 5 volts and a maximum of 0.5A with the old USB 2.0 standard. This means a maximum of 2.5W. Back during this stone age, any USB port that delivered more than 2.5W was potentially labelled as 'fast charge', but was generally anything 5W and above.

Then came various fast charge standards. Qualcomm's 'Quick Charge' from 3.0 upwards was specced at 18W, whilst USB PD is currently(!) up to a staggering maximum of 100W (and soon to be 240W) delivery at 20V. USB PD 'range 1' is up to 15W, and 'range 2' is up to 27W.

Then you have wireless 'Qi' charging. Qi 'BPP' delivers up to 5W, whilst Qi 'EPP' is up to 15W.

12V USB adapters
All 12V USB adapters convert the bike's 12V power delivery to at least 5V for USB devices. This means that (theoretically for a 100% efficient adapter) that 12V/1A will be converted into 5V/2.4A USB output. They are literally DC-DC transformer circuits. In theory, the Tracer/Niken's 12V/2A DC fused circuit can deliver up to 5V/4.8A DC to a USB device through a 100% efficient adapter before the bike-side fuse blows.

USB device maximum power draw
Here is a table of indicated maximum power draw for charging/powering various electronic devices via USB.
iPod Classic: 4W
iPhone 6: 5W
Nokia 2.3: 5W
Pixel 1: 10W
Pixel 6: 13-22W
iPhone 12: 15W
Galaxy A30: 15W
GoPro Hero 7: 10-15W
iPad Air 4: 20W
Galaxy S21, S22: 25W

As you can see, all except the Samsung Galaxy S21 and S22 can theoretically charge at their maximum power draw without blowing the bike's fuse. However, you can still safely charge the S21 and S22 if you limit the USB output to below 24W total.

Sample 12V-to-USB adapters
Here is my 12V chode collection.


Left to right:
Belkin 5V/1A (5W)
TomTom 5V/1.2A (6W)
Comsol 5V/2.1A single port (10.5W)
Mumuso 5V/2.4A dual port (12W)
Mumuso 5V/2.4A dual port (12W)

I can't tell if the Mumuso adapters split the 12W between 2 ports (i.e. 5V/1.2A), or whether it can deliver max 12W to a solitary port. Regardless, I have used all 5 chodes to sufficiently power a mobile phone at maximum screen brightness and keep my iPhones at 100% charge.

Looking at Amazon: I have seen adapters that claim to deliver 18W to 24W via a single USB port, which should also be fine for the bike. I'd be hesitant to run anything higher than 18W personally, when there's no real benefit for most devices.

The following 2 examples could potentially blow your 2A fuse if you are trying to charge a Galaxy S22. Check out their claimed maximum power outputs.



One can definitely 'fast charge' above 5W from the switched 12V accessory port on the dashboard without going all the way with rewiring a new harness - but there are definite limits to what type of adapter and device you choose. There are also other good reasons for fabricating a separate circuit harness such as weatherproofing, port location, port type, and application (such as SAE plugs with higher rated in-line fuses for heated clothing and battery chargers, and full 100W USB-PD for running a laptop).

Edited by KellyL
Minor corrections
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Whoa, what a fantastic write up!  Thanks for that

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2015 FJ-09 / touring bags / oil plug mod / Evotech rad guard / SW Motech bash plate / VStream touring windshield / Seat Concepts:  Sport Touring / Vcyclenut ABS rings (speedo correction) / Cosmo RAM mount

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Posted (edited)

Another thing worth mentioning: it's unlikely that any 12V USB adapter is anywhere near 100% efficient in conversion. It's next to impossible finding efficiency ratings for these cheap-ass things. So it's worth adding a fudge factor before choosing one based on its claimed power output.


Let's assume that a 'Quick Charge 3.0' adapter with a max USB output of 18W (9V/2A) has 80% efficiency. That would mean that at max output, it could draw 22.5W (12V/1.875A) from the bike's charging circuit (18 / 0.8 = 22.5). This is approaching the current at which the 2A fuse will blow. The majority of the time it will be perfectly safe though, if using it to power a 15W device like an iPhone 12 (5V/3A).

I would therefore be very cautious with running a '24W USB output' adapter in combination with a 24W or more device (like a Galaxy S22) as I'd then be running at the ragged edge.

Edited by KellyL
Corrections again
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49 minutes ago, peteinpa said:

I'm going to add that if you charge your phone with the bike off you'll come back to a charged phone (maybe) and a dead bike.

Its a switched outlet.  If the key is off, the outlet has no power.

***2015 Candy Red FJ-09***

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5 hours ago, peteinpa said:

I'm saying if you wire directly.

Interesting point. The Tracer battery is rated at 8.6Ah capacity, which is about 103Wh at 12V. About 50% is useable (51.5Wh). An iPhone battery is around 11Wh, and an iPad battery around 29Wh.

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Good write up, and that "someone here" was me, I wasn't intending to get into a debate about the merit 12V adapters and power standards. But you seem to be calling me out and I don't mind owning a mistake if I made one with something that I said since I seem to have offended you enough to create a separate post; I will throw the thread up here for other people to read and see for themselves:

I said the 2A fuse was weak and that my tire inflator blew it. I did not say that charging my phone blew it. My solution was a separate adapter to connect to an SAE pigtail that I put a 15A fuse in. It's a specific use case separate from charging a phone.

The AUX socket slow charged my OnePlus 7 Pro and currently slow charges my S21 (as you pointed out it should). I was presenting an actual real-life use case that I experienced where the 2A fuse wasn't enough, and maybe the OP had the same; they later then said that it didn't matter. Sharing my experience wasn't wrong, it's literally what I went through.

Now onto brass tacks: If you take an issue with my statement "and slow charges most devices" I still stand by it, I'm 0/2 with my phones. And it's a bit misleading for you posting a list of older electronics, mid-range devices and Apple (who has historically used their own "standards" rather than follow Qualcomm's QC) products to prove your point, when a list of android flagship phones from 2019+ would look very different. You even use Qualcomm's Quick Charge 3.0 in your post as an example; that was released in 2015 man, we're on QC 5.0 now.

Even with your example of the S21 and S22, 25W is the not the fastest speed those devices can charge at. Both of those phones can charge at 45W if the adapter supports it. Apple can call 18W "fast" charging all it wants but that's slow by today's standards, and in my opinion it is disingenuous for you to use that in your example. It's like the FCC considering broadband in the USA to be 25Mbps/down and 3Mbps/up; no one sane would consider that proper broadband speeds.

Next: Qualcomm's Quick Charge 3.0 from 2015 can support a max power draw of up to 36W, and in 2016 came QC 4.0 going up to 100W; of course it is up to the connector to regulate the current as you have stated in your post. You'll recall that in the previous link for the S21 specs that Samsung has 15W, 25W, and 45W charging modes depending on the adapter. And this brings me to the point I was trying to make saying "and slow charge most devices" regarding plugging a 12V adapter into our AUX port: at the end of the day if it's only able to push 24W in 2022 when flagship Android phones have 2x or faster charging speed capabilities then it's "slow" charging and I will die on that hill.

Really this is all a long-winded way of saying that I consider anything less than 30W to be "slow" charging in 2022. I expect people to have phones that support that; especially since my warp charger adapter for my OnePlus 7 could theoretically support 30W through 5Vx6A but it defaulted back to 5Vx2A in the AUX socket back in 2019. Maybe it's a mistake for me to assume that and I'm sorry if that offended you personally. But if "fast" charging for you is anything above 5W like you state in your conclusion then more power to you... pun intended.

But none of this matters because I was previously just trying to share an experience I had with the AUX port not being up to the task for what I was trying to plug into it 🤪. Honestly a $14,899 machine that went through a total revision in 2021 should not have the same 24W 12v 2A AUX port that came with the original model in 2015.

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This post is an expansion of an interesting topic that emerged from another thread, and one that hasn’t been covered in detail previously. I acknowledge that as an introduction. It’s also a courtesy so as not to hijack someone else’s thread.

How this academic exercise is interpreted is beyond my control. The only “calling out” seems to be done by yourself. And in that thread you recommended a 12W USB output cable to petshark as a fast charge solution, which can also be achieved via the switched accessory port - and by your reply here is no longer fast charge.

Nevertheless your reply here is full of good information too and this is appreciated. It’s unfortunate that you’ve chosen to interpret it as a “die on a hill” ego battle. I guess that’s forums. 🤷

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  • 3 weeks later...

You're welcome!

Perhaps a discussion for another thread, at another time... but one needs to take care when choosing to wire high-draw powered accessories into the bike. I haven't been able to find exact figures on the FJ09/MT09 stator, but general guidelines state around 300W (+/- 25%) at 5000rpm 3-phase AC prior to rectification for a light-mid street bike. Basic electrical functions could draw anywhere between 150-200W. Heck, turning on your heated grips to full will use 30W (10% of output). (I know on my old Z900 that Kawasaki didn't offer heated grips, because the stock stator was too small to support them.) And as petinpa mentioned, it's not difficult to drain the battery by watching a Netflix movie or two with a phone connected to the bike.

I know there's a lot of chat over at advrider on calculating accessory allowances. I'd be keen to hear more Tracer-specific info from the good people here.

Edit: and just to put this in context, Electrosport quotes 400W output and 300W running draw for a stock FJR1300, leaving only 100W for accessories. And a BMW R1200GS puts out over 700W from an alternator… 🤯

Edited by KellyL
Electrosport reference
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