Ignition Switch Current Protection

HalcyonDaze

I need some circuit help. I've built a module to start a motorcycle via rfid tags using a bs2 stamp and the parallax RFID receiver, to be powered by the on-board lead cell battery. But my circuit skills are still pretty basic, and before I wire the thing up I want to make sure Im not going to fry anything.

So what steps do I need to take to protect my system from the massive currents involved?

I have a 5v regulator between the stamp and the battery, but should I be thinking fuses or something too considering the instability of a cranking car battery?

For the Start output can I get away with a transistor to get me up to the currents we're talking, or do I need a relay? Will a relay in close proximity cause interference or damage to the RFID antenna?

I also need an input to confirm the Running state of the bike. Do I need anything more than a big resistor to hold the current down, or should I be thinking relays, fuses etc on that end too?

EDIT:
Im not really concerned with security for this. All I need is start it without having to physically touch the bike in any way; the only reason I didn't just go with a mag switch and a big permanent magnet was that I was afraid of other stray magnetic fields flicking it while the thing was already running. And I mentioned the RFID portion of the project because any relays will be basically right up against the antenna and the stamp, and I didn't want the relay coils to damage or interfere with them.

My current design was using the bs2 and switching transistors to power on the bike and send the starter a signal, but those things have a max current rating of 800 mA, so I'm trying to find a small footprint way to safely switch (and isolate) a higher current line to act as the ignition switch. I don't expect the LDO to actually source that signal, just to power the RFID, the bs2, and as little of the transistor/relay branch of the system as possible.

Mike Green

First of all, you probably need to think of the RFID system as a lock on the ignition and you're still going to want to have some kind of heavy duty switch that does the work of turning on the ignition system and another switch or section of the switch (with a momentary contact) that cranks the starter. The RFID and Stamp turn on a high current relay when a valid RFID tag is read and this relay remains on until the Stamp senses that the power is turned off to the ignition switch. This way you don't need to sense the running state of the bike, just whether there's power present at the ignition system input. The ignition switch can be one 3 position switch with an OFF-ON -Momentary ON and DPDT with one pole switching the power to the ignition system and the other pole activating the starter (how much current does that take anyway?) You could also use two separate switches, one a pushbutton switch for the starter and the other a toggle switch for the ignition system.

HalcyonDaze

The idea behind the module is specifically to replace the manual switch with a RFID/microprocessor initiated cycle. The security lock feature of the rfid is a secondary benefit to the the no contact starting requirement. I'm looking to be able to hold the rfid tag near the antenna to power on the bike, then as long as it stays in range to act as the momentary switch for the crank cycle. Then, once the tag leaves range, it acts as a shutoff switch that requires you to hold the tag in range for a minimum of a few seconds to power off the bike. Then is stays on, drawing a negligible (hopefully) amount of power, as it waits for the tag to arrive and start the bike back up. There would be an emergency shutoff button for the bike power, and a switch to power off the antenna for long term storage, but other than that Id like to avoid any manual switches. I was thinking something along the lines of the solid state relay setup on the Digital I/O Board kit I saw in the Parallax catalog.

sam_sam_sam

I would power the Basic Stamp and RFID reader with a switching power supply


http://www.futurlec.com/Mini_Power.shtml

HalcyonDaze

That adds a lot of bulk to the package. Whats the benefit of that over just the 5V LDO regulator?

Peter KG6LSE

it can be done . use the default RFID code and have it set a bit to be on or off .



then as far as the Hardware . Sam has a point ..SMPS is way more eff and Beacause you are rinnung off a Shoe size Lead acid Batt you need to suck every mA you can !


the losses in a LDO is still IMHO to high for a app like yours .

IF I was doing this I would set it up so that You get on the bike and press ( go ) to read the tag . at the same time that Button is ignition that is enabled by the ( OK ) bit set by the reader .
then as soon as the reader looses the card it will stop the bike .

this way the reader is not on till you ask it to . do the chance of a dead batt is MUCH less . then as soon as the bike is running the reader wil be on all the time ..



this is not BS2 code but a idea on how to knda flow the code in a way




First check to see if the bike is runing If so then check the tag . if tag OK then check to see if the bike is running If not then check the ON button. if on button is good then check tag .
if tag is good then GOSUB start bike .If on button is bad then go to the top of the program




this is start .. I may not work as shown but it may help


Peter ..

camarokenny67

first most automotive/bike starters can pull up to 250 amps so relays are a must with redundant fuses however the signal wire to the starter is all thats required to start the bike/car and its just a 5 volt refrence signal less then a few amps (i would say about 10 max,but it depends on the vehicle ). for the relay rfid power source etc second in my opinion i would leave the rfid to wear it only controls powers the ignition system . i know they dont have a range of more then a foot or so for most ,or so i undestand. on most of the cars i work on the rfid chip just has to be in the car somewhere ,even the trunk lol and then you can utilize the push button start .added benifit is if u fall off or get jacked the bike wont stay running with out you so it would replace just the key and the only thing after that if u wanted more security would be a servo to lock the steering when u move far enough away from the bike

i hope i helped

sam_sam_sam

The reason I said to use a switching power supply is that I have a Gate Opener that uses a RFID reader with a 5 volt regulator and had to use a heat sink on the regulator and it get very warm

HalcyonDaze

camarokenny67 wrote: »

first most automotive/bike starters can pull up to 250 amps so relays are a must with redundant fuses however the signal wire to the starter is all thats required to start the bike/car and its just a 5 volt refrence signal less then a few amps (i would say about 10 max,but it depends on the vehicle ). for the relay rfid power source etc second in my opinion i would leave the rfid to wear it only controls powers the ignition system . i know they dont have a range of more then a foot or so for most ,or so i undestand. on most of the cars i work on the rfid chip just has to be in the car somewhere ,even the trunk lol and then you can utilize the push button start .added benifit is if u fall off or get jacked the bike wont stay running with out you so it would replace just the key and the only thing after that if u wanted more security would be a servo to lock the steering when u move far enough away from the bike

i hope i helped

Im not really concerned with security for this. All I need is start it without having to physically touch the bike in any way; the only reason I didn't just go with a mag switch and a big permanent magnet was that I was afraid of other stray magnetic fields flicking it while the thing was already running. And I mentioned the RFID portion of the project because any relays will be basically right up against the antenna and the stamp, and I didn't want the relay coils to damage or interfere with them.

My current design was using the bs2 and switching transistors to power on the bike and send the starter a signal, but those things have a max current rating of 800 mA, so I'm trying to find a small footprint way to safely switch (and isolate) a higher current line to act as the ignition switch. I don't expect the LDO to actually source that signal, just to power the RFID, the bs2, and as little of the transistor/relay branch of the system as possible.

sam_sam_sam wrote: »

The reason I said to use a switching power supply is that I have a Gate Opener that uses a RFID reader with a 5 volt regulator and had to use a heat sink on the regulator and it get very warm

Interesting. Ive been using them for a while and never actually had to use the heat sink features yet. What current was it running? Was it actuating a lock, or a full swing arm motor?

Peter KG6LSE

I use a BOE and a RFID and serial display with my BS2 as a dorm lock and stuff . the Onboard TO-220 reg gets rather hot too.


Here is a pressing issue . Your batt in a bike is around 17 Ah or less . That Batt is not going to last well with 100+ mA loads of the reader and the stamp ....... you may run in to starting issues in the cold if you did not use ( charge ) the bike in a week .
.
So you may need a switch to enable the whole RFID system . so that its not doing a constant drain . a seat switch my do the job in a simple hidden way .

use a 555 as a pulse strecher . so that if you hit a bump it will not kill the bike , ill say a 2 second delay for now.

Use Logic input MOSFETs to drive the relays . IR has a TON of them and are way better suited for this kind of work .

Peter ..





is not goig to be happy with a 200mA or so load . what is a Bike batt 17 AH . its not much and after a few days It wil be dead enough where it may not start the bike .

vaclav_sal

HalcyonDaze wrote: »

So what steps do I need to take to protect my system from the massive currents involved?

A comment from Peanut gallery.
Ever heard about "Bendix"? Unless bikes use different technology - the starter (Bendix) is connected to battery via a relay that carries the actuall starting current around 100 or more Amperes.

This relay is activated with much less current, but still not directly driveable by processor output.
Also the mechanics of the starter prevents the starter to engage the flywheel when the motor is running,
ableit with some unplesant noises! So if accidental "bumping" of the starter is a concern - introducing some reasonable delay in activation ( similar to button debounce ) would do the trick.