Voltage surges

[tris]

Afternoon All
Some of you may know that I've left the MG fold (F800GT BMW) but I have a question that someone here may be able to answer.

My new bike has a Canbus system that controls everything,  including the factory fitted DIN connector which has a 5A limit.
I have a small tyre compressor that I'd like to carry, and when bench tested happily runs at 3.5A
However, at startup it surges to 10.5A which will cause a trip.
How can I reduce the start-up surge to something more Canbus friendly?
Cheers
Tris

[guzziart]

SAE connector directly off the battery (w/15a fuse) and pump, plug-in when needed.

Yeah, I can't think of any way to lessen inrush current to your device upon start up.

Art

[Stretch]

What Art said.....

[tris]

So, aI've found a solution

I need a Negative Temperature Coefficient (NTC) Thermistor

When cold it's resistance is high reducing the current flow but as the compressor runs over a short time the Thermistor warms up and the resistance drops
They're designed to manage an excess inrush current

See 3/4 way through this
https://www.electronics-tutorials.ws/io/thermistors.html

As a Mechanical Engineer I just need to work out which one I need!!!

[Wayne Orwig]

So, aI've found a solution

I need a Negative Temperature Coefficient (NTC) Thermistor

When cold it's resistance is high reducing the current flow but as the compressor runs over a short time the Thermistor warms up and the resistance drops
They're designed to manage an excess inrush current

See 3/4 way through this
https://www.electronics-tutorials.ws/io/thermistors.html

As a Mechanical Engineer I just need to work out which one I need!!!

Which means the compressor motor may be stalled by the low startup voltage, and never start spinning. Maybe.
Which means that if it does operate, the thermistor must, by design, remain VERY hot to keep the thermistor voltage drop low. So there will be a significant voltage drop to the compressor when operating, just to keep the thermistor smoking hot. Plus you need a box for it that can handle all of that heat.

Have you checked the current draw of the compressor under full load (an inflated tire)?

It is so easy to put a SAE connector on the battery, to charge the battery, or run a compressor.

[kingoffleece]

Exactly.  Don't over complicate it.

[ridingron]

SAE connector directly off the battery (w/15a fuse) and pump, plug-in when needed.

Yeah, I can't think of any way to lessen inrush current to your device upon start up.

Art

Quick, cheap and easy. A very Guzzi solution. 

[moto]

...
Have you checked cthe current draw of the compressor under full load (an inflated tire)?

It is so easy to put a SAE connector on the battery, to charge the battery, or run a compressor.

I don't think CANbus was meant to charge batteries or run compressors. If you decide to go the way that everybody's recommending, I have a tip or two. Get a 3 foot 14 gauge connector. I played with voltage drop software on the internet and decided that would be enough for my compressor. Also, watch out for the polarity of the cable you buy. Many of them are intended for solar panels and have the polarity reversed. Sorry if this is obvious to you already.

[Kiwi_Roy]

As others have pointed out Canbus is not intended to power this type of a load, if you are not careful it will be destroyed/
A DC motor will always draw a high current at startup when full Voltage is applied then as it gets up to speed the motor generates a Voltage in reverse (Back EMF) so the current drops back.

[tris]

Thanks everyone,  it seems that a change of direction is needed!!!
I'll sort something out wired directly to the battery.

As an aside what is this DIN socket supposed to be for?

[twowings]

https://www.hexezcan.com/

https://moto-mate.com/technologies/made-easy-motorcycle-can-bus-controllers/

https://denalielectronics.com/pages/denali-cansmart-canbus-controller

[moto]

Thanks everyone,  it seems that a change of direction is needed!!!
I'll sort something out wired directly to the battery.

As an aside what is this DIN socket supposed to be for?

That socket might be for electrically heated clothing.

But, backing away from my previous position, it might also be for tire pumps. The canbus can certainly switch on a high amperage circuit when it wants to, and then it is probably set up to monitor the voltage or current to make sure things are OK. It could well allow for a startup surge of voltage or current, depending on how it's programmed. The 5 amp rating would be for a continuous load.

I think the best bet is to ask somebody who knows about your BMW. Maybe the dealer knows whether you can put your tire inflator on there, or maybe there is a knowledgeable online forum of BMW owners that would have that particular answer.

[John Croucher]

Buy a co2 tire inflation kit. No electric problems.

[tazio]

Buy a co2 tire inflation kit. No electric problems.

Yes, they saved my bacon in the middle of W.Virginia trip, a long way from home
And, if your bike doesn't have one, a cheap TPMS can give you a heads up before you hit the next tight curve.
Ask me how I know..

[kingoffleece]

https://www.motorcyclegear.com/parts/aaron's_garage/handy/lexin/p5_tire_pump.html

I carry this now.

[kingoffleece]

Got it in a small case with everything else that's needed.  Goes with me whatever I'm driving or riding.

[Kiwi_Roy]

I have a small portable compressor, I threw away the plastic case it came in, shortened the hose and just touch the two wires direct onto the battery terminals, it doesn't care which way it runs.