Topic: What is resistance of CB400F starter relay?

[krksquared]

I'm trying to figure out just how much current the starter switch has to handle. Guess I'm a little lazy tonight & hope someone has already measured one. If not, I'll check it this weekend. I'm thinking that maybe it would be wise to fire the starter switch with a relay instead of direct. I'm going to use relays for my headlight as I found that there is a 2v drop between the battery and the headlight low beam contact and a 2.7v drop at the high beam contact. Not an uncommon problem in low voltage/high current circuits. I once had a Lotus Europa that had a 4v drop to special high power lamps. Easily solved with a relay. Yes, that 2v drop to the low beam makes a substantial difference in lamp brightness.

[Bodi]

First, no idea on the starter relay coil resistance or load current.
I've "fixed" many starter switches that have failed. I believe they all overheated from the headlight current going through the NC contact for shutting the headlight off while starting, corrosion/aging causing contact resistance causing heat causing more corrosion causing higher resistance causing more heat etc... until the plastic switch frame fails.
I either install a new switch (NLA) or put in a SPST momentary button that fits in the original button hole, deleting the headlight off function with just the switch or adding a relay if someone really wants that to still work.
I have never seen any sign of damage to the starter contact in the switch, it does get a bit pitted from the inductive kick of the coil but even after 30 years of starting that's not too bad.
So: I think that for this very low duty switch with apparently conservatively rated contacts, using a relay is not worthwhile. Yes, the headlight dims quite a bit with a 2V drop (P=E²/R) and we want all the light we can get. But as long as the relay pulls in and the starter motor whirs, what does it matter if it's getting a wee bit less than full battery voltage? Adding a relay adds a point of failure and more wiring that dopesn't match the wiring diagram.
If you do want to keep the headlight-off-while-starting function, a form C relay is an excellent idea. Running the headlight power through the start button was not a good idea. If you already have a headlight relay this will complicate the circuit, of course.

[strynboen]

yes the thin vire in the coil magenet cant suck anything then miliamps..have not ohm testet one...but it not a kritical powerlevel vho goes through..any small breaker can do the job..its more vater restistens and korosion vho make problems..not amp flow

[krksquared]

To clarify, my starter switch works fine. What I'm investigating is how much current the starter switch has to handle. If it's a lot (relatively), switching a relay will cut it from amps to milliamps. All this so the no longer available starter button switch will last so much longer. A 12v 15a form A relay costs less than $2.

[robvangulik]

Why would you switch a relay with another relay? You use it only once for every ride, it has worked fine for 40+ years and will probably work fine in 40 more.

[krksquared]

Why? To reduce the energy the starter switch has to deal with. A typical relay I would use would have a 225 ohm coil. At 12v, the current to operate the relay would be 53ma (0.053a). If the starter relay is 8 ohms, current to operate it would be 1.5a. Assuming simple DC conditions (not actually true), the switch will deal with 18 watts direct as opposed to 0.64 watts to a relay. Because the starter magnetic switch is inductive, (probably not much), there will be a back voltage the switch will have to deal with. In my many other endeavors (sports cars, short wave radios), I've had to deal with pitted switch contacts. Often a replacement switch is unobtainium. The pitting is caused by arcing or sparking which is a result of the magnitude of the energy being switched. If the switch in this discussion was easily obtainable, I would have never posted this query. I hope this all makes sense 

[scottly]

IIRC, the coil resistance of the starter solenoid is 3 ohms.

[przjohn]

Are there Starter Switches burning out left and right on these bikes? I just don't see the need for a double control circuit for the starter on these bikes, seems to be fixing a problem that doesn't exisit.

[krksquared]

Precisely. I am thinking about fixing the problem before it exists. How long do you expect a 42 year old push button switch to last? Another 42 years? BTW, I just measured the starter solenoid at 3.28 ohms which will result in around 4a.

[strynboen]

ok,, a lot more amps,, then i thorth

.but still it are aktivated for 5 sekunds..kontaktors in the relæ vil be burned at mutch as in the press buttom...so no safty in that.

.but stil ..overkill to build a relæ to pull an other relæ.

.in Europa ve dont have mainlight over the start buttom.so have no problems vith burned aut kontaktors..it are plastic go brittel..and korosion in the soldering/viring..not any amps rating problems

.i have more hella/bosch 30 amp rated relas failing over the years in my car..so to build one  in a bike..vill just make  problens ..komplikating vith one more komponent, vho can fail.
..the one place a relæ is making good sence is to delever the coils full battery power.(and safe the kill kontaktor for the amps).its make full sence..and give a lot of power..a real need to upgrade somthing..and take the risc of faling komponent(..its easy to revire..even on a ride)

[Bodi]

Those starter switches are not close to being overloaded or damaged by the solenoid coil current. In many models the solenoid coil current also goes through either the clutch lever switch or the neutral switch, neither prone to failure due to it.
The start switches that also switch headlight power are likely to overheat and fail though, and adding a relay to take the headlight current - or rewiring so the headlight stays on - is worthwhile. The added (not eliminated?) headlight load doesn't seem to affect starting.
If you want to add a start relay, go for it. But there's no switch problem requiring this.

[TwoTired]

I've taken apart several start button assemblies.  Even those with the headlight interupter showed no sign of contact distortion over the 40 years of use.  This demonstrates that the contacts are rated well beyond what the standard useage needs. I can't say the plastic surround was nearly as durable. But, the contacts still had their original contour. For sure these weren't operated with high watts headlight, though.

I agree, a relay to operate a relay, makes no sound engineering sense.  Even the headlight, if remaining at stock amperage draw, doesn't need a relay, as I found no evidence of contact heat degredation there either.

When I still was employed as an engineer.  I had the occasional task of acceptance qualifying switch components for use in our products.  I recall testing input mains switches from various vendors.  What became apparent was a correlation of contact size and spring pressure that was related to current handling durability.  Switches with small contact mass had far more current related failures than those with larger contact pads.  Given the examination of hundreds of switches, I submit that the Honda starter contacts are rated at about 7 amps repititious duty,  and the larger headlight contacts are rated about 10 amps repetitious duty.  For stock application duty, these ratings are about double what the affected circuits normally carry.

In summary I don't see a need for an engineering change to add more relays to either circuit, unless you are also making other changes in power usage for the affected circuits.
If you have an old starter button switch to disect, inspect for yourself the switch contact condition for signs of stress.  If stress is found, then consider a way to alleviate.  Otherwise, leave a good working design unmolested.

Cheers,

[PeWe]

I added 5 relays on my CB750 K6, but not for the starter.
3 relays for headlight (HI+ LO+ 12V off to Parking bulb in headlight reflector when LO is ON to ensure good light pattern). I did not trust 5A thru the handle bar switches either. (No problem before during the 11 years I have used it without)
1 relay feeding the ignition coils. Relay controlled by ign switch that I needed to give amps relieve, aftermarket ign switch.
1 relay for my dual snail horn that needed thick wires from battery, both 12V and -.

All relays have own thicker wires (2.5mm2) from battery with an own fuse close to battery. Headlight share same hanging fuse.

[Jore]

I have relay to control the starter solenoid on my 400

[krksquared]

Ok, as the OP on this topic, I feel a need to respond. I hope no one got the impression I was recommending a relay be used to activate the starter solenoid. I was investigating if it might be worthwhile by trying to find out how much current the little switch had to control. That’s why I asked for info on its resistance so I could calculate the current.

As for fixing a problem that doesn’t exist, I was trying to determine if there is a potential for the problem to exist. These switches are probably not burning out left and right but my thinking was to stay ahead of the possible problem.

No, the contacts in the solenoid will not be “burned” as much as in the little button. The solenoid has much larger contacts to handle starter motor current. The little push button switch only has to handle the solenoid coil current. Two different circuits.

As for the solenoid coil current going thru the clutch lever switch or the neutral switch, that’s a non issue because those switches are either closed or open when attempting to start. Open - no current, no spark, no start. Closed - current, no spark, start. The only part that sees any stress is the little start button.

Twotired (I love that name) you make good points. As a retired engineer (I’m still a working one), I think you get where I’m coming from with this analysis. Hey, at least I didn’t propose going with an IGBT. Got some big ones. How about an SKM300GB? Heck, with that I wouldn’t even need the solenoid. For now, I’m leaving this part of the bike stock as I don’t think 4a is much of an issue.

PeWe, you are relay my kinda guy And Jore, you did it. Why?

Thanks everyone for your thoughts!

[PeWe]

The starter motor on a CB750 is specified 600W. 600W/12V=50A   CB400 maybe not much less.
I have replaced it with a stronger one from a CB900 DOHC that has 800W motor, 800W/12V=66,67A.

The starter is not used that long but wire to starter must be rather thick to deliver that amount of Amperes. Good ground connection needed too so the minus cable from battery must be connected to a good location for both engine and frame.

[krksquared]

Maybe this will help some folks. What I don't understand is how the Starter Switch works. As drawn, it doesn't make sense to me. It needs to direct power to ST2. Is it a SPDT with ST1 the pole? If so, depressing the switch would put regulated power to ST2. Also, HL would get disconnected and the headlight would go out. On my bike, the headlight stays on.

[strynboen]

us modells only......
edit ..yes ve have a ekstra  off/pos/light-kontakt posision in Europa.(.and parking light posision in the main key)..but not a stering Lock..in the main key

[Bodi]

Krksquared yes it is a spst switch connected as you describe. I only see NA models and don't know what other markets did. Do you have a headlight on/off switch? We don't. That type might not have the headlight through the start switch.

[robvangulik]

us modells only......
edit ..yes ve have a ekstra  off/pos/light-kontakt posision in Europa.(.and parking light posision in the main key)..but not a stering Lock..in the main key

And i for one am very happy with that, wouldn't have it the USA way

[Jore]

I'm running one because I redid the wiring on my bike, and the original push button for the starter had burned out or something before I got the bike, so the PO replaced it with a mini push button that wasn't able to handle the current going through it so after say 3-4 cranks it would burn and the little spring would come flying out, so I installed a relay to prevent that.

[PeWe]

us modells only......
edit ..yes ve have a ekstra  off/pos/light-kontakt posision in Europa.(.and parking light posision in the main key)..but not a stering Lock..in the main key

And i for one am very happy with that, wouldn't have it the USA way

This work fine. Possible to upgrade a US bike with! OFF-Parking -Light on
https://www.ebay.co.uk/itm/Honda-CB-500-k2-750-four-k6-f1-Handlebar-Switch-Right-NEW-SWITCH-RIGHT-SIDE-NEW-/291753832001?_trksid=p2349526.m2548.l4275

Hi-Lo on left side as usual. (Honda K6 left has Hi flash when pushing horn knob sideways.)

[TwoTired]

The starter motor on a CB750 is specified 600W. 600W/12V=50A   CB400 maybe not much less.
I have replaced it with a stronger one from a CB900 DOHC that has 800W motor, 800W/12V=66,67A.

The starter is not used that long but wire to starter must be rather thick to deliver that amount of Amperes. Good ground connection needed too so the minus cable from battery must be connected to a good location for both engine and frame.

Be aware those motor ratings are not for continuous duty.  Isn't there something like a 30 second duty period?  Further, the circuit must handle motor stalled current loads, which is 280A, according to the 750 Honda Shop manual.  That includes the solenoid contactor.

But, this is off topic from a CB400F starter relay exciter winding...

[strynboen]

yes think peak amp is far heiger..specily if the volt falls to ..just say 10 volt..or kold frost make the oil thik..is the amp rating vith a engaged motor load..or free spining??..the DIN standarts use to be fuld load and SAE free spinning..if it is a bit like like hp/kw messurung...just to go more off topic