zener diode help

twhitehousescat

yup that pic was the easiest to read , but not understand

the bike has been rewired , digi dash that used gps , the lamp is the latest euro 4 spec with a modern h4 bulb , 35/35w , the original bulb was a b20b 35/35 w , I have fitted a 1/2 size relay (as shown in this thread) inside the lamp body the relay is triggered by power from light switch and bulb gets direct feed from battery via a fuse - thick wire and then the relay , those bikes are notorious for volt drop , when std , power to ign then to light switch then to dip , i have removed the ign switch and light switch from equation

I want to be able to use h/light when I want , not as per new regs , on all time unswitched , there is a superbright led in sidelight that is on all time (thats good)

I only have small battery 4ah (motobatt - the best) but cranking power is much lower than the modern bike , with light powered by pulse from ecu , those bikes are 9ah

I often leave light on , and in past have struggled to start , with light off every thing is good

35w = 3 amps , thats a lot on a 4ah battery when you are using starter

the engine shown in that pic is BRAND new with factory fitted alternator and genuine (not china) reg/rect , I believe (from memory) about 120 -180w alternator , all bulbs apart from head are led

that

you could just put a pressure switch under the seat, so that when u sit on it the relay will turn on?

decades ago there was some big horrendous electronic circuit that measured micro (nano volts???) volts. you get 2 wires and put one the battery ends the thick + wire, and another on the voltage regulator + side. it would give an output depending which line had the higher micro volts. In your case when starting, the battery side will have a ever so slightly higher voltage, as nothing will yet be generated. When the engine kicks in the voltage regulator starts to work, the regulator will have a sightly higher voltage as the current flows to the battery.

twhitehousescat

that wrote: »

you could just put a pressure switch under the seat, so that when u sit on it the relay will turn on?

I think we are now scratching our brains

that idea is far from what is required , for a start , you SIT on the bike to start it , and every time you go over a speed bump and lift your bum off the seat , you do it in darkness

Heedtheadvice

Well that was a good bit of lateral thinking by polymaff for a really simple solution:
(1) A second rectifier: Unfortunately, as witnessed by twhitehousescat the headlight poser is provided by alt output and non by the battery and suffers when the alt does not give sufficient output. Risk Lights out! Or at least dim.

(2) Schottky low volts drop diodes. Prevents the headlight draining the battery but again gets all it's power from the alternator and therefore suffers at low revs as above.
It seems essential that at tickover the headlight power comes from the battery....for short(ish) periods!



It is a bit disappointing that the thread question is a long way from it's title implication, information is only slowly being produced for posters to offer solutions (it would have helped had it been possible to give lots more up front....but we are more or less there now) and no solution has been accepted!


May I ask what is wrong with my solution? The only thing that now transpires since I posted earlier is where I show output to the light, the OP updated to say that the battery feeds a relay within the headlight housing. No issue with that.....should still work! I am more than happy if someone is critical to show any error or improvements with a view to solving the requirement. Fire away and then let the OP use it!



Or is it just my pointing out the real risks that have upset twhitehousescat into rejecting it? :eek: The risks are more to do with the design requirement than the practicality of making it work/refining it



Get off the fence twhitehousescat, hop along to CPC, buy the bits, build it and refine it if needed!! :j:)

twhitehousescat

https://ibb.co/vjqk1Mh



slightly to complex for my mechanicing skills

twhitehousescat

well an update , been reading the tech book , bit vague bit mentions "ipto 70v at 5000 rpm , is that each wire or not?

what was suggested to me by someone was a "buck converter" , ebay throws those up , but min voltage is 85v https://www.ebay.co.uk/itm/AC-DC-12V-450mA-5W-Power-Supply-Buck-Converter-Step-Down-Module-K/282988785520?epid=2164860856&hash=item41e3722f70:g:f24AAOSwh9FbD5Od

output would not matter as it would just be tripping a relay

so , has anyone seen , like the above that work from say 12v AC to 80 or 90v ac

forgotmyname

Alternator --- diode --- relay or direct to the lamp if the diode is big enough. why make it hard?

Relay can be switch fed so it only comes on when you switch it on or direct so its always on when the alternator is working.

Smart charge relay was an unbranded item listed under RC equipment on ebay some time back. But is a similar to the cheap TEC3M style units only smaller. The TEC2 or TEC3M units only only 40mmx40x20 in a case and you could trim that down a lot and simply heatshrink it to protect it.

This may do the job.... https://www.ebay.co.uk/itm/201682811254
Mine has 2 relays and only one trim pot for the voltage though.

or maybe...https://www.ebay.co.uk/itm/222382863130

twhitehousescat

https://www.ebay.com/itm/DC-Buck-Converter-Step-down-20-70V-to-2-5-58V-Power-Supply-Module-30A-800W-/253234957355

working on AC , not Dc side as battery voltage will fluctuate with lights / indicators etc

forgotmyname

The battery voltage wont vary much at all unless you have a heavy load and no charge or a duff battery.

Got an old 8Ah SLA battery here, fairly discharged @12.3 volts, pulling 4 amps for a peltier element the voltage dropped to 11.7.
Fully charged i would expect the voltage to remain fairly stable and above 12.5 volts. Thats without an alternator adding any additional power.

Your overthinking things or we dont have the full picture. You already have a DC voltage from the regulator and a storage device (the battery) to keep the voltages fairly stable and above 12.5 volts except maybe briefly when the starter is active.

Your worried about the split relay being big but put a link to a 30A buck converter? I have something similar its about 120mmx55mmx50mm.

forgotmyname

This ones 130x55x48 not including the 3D printed fan mount.
20Amp version.

http://forgotmyname.50webs.com/VT661/Volt1.jpg

http://forgotmyname.50webs.com/VT661/Volt2.jpg

http://forgotmyname.50webs.com/VT661/Volt3.jpg


Puzzled why you need one of those though? And isnt that a DC-DC? So you still need a rectifier and what voltage are you setting it to? 12V DC that you already have?

If its just to auto switch on the lights with the engine running its far too complicated, dont a lot of bikes do that anyway?