RELAYS - Latch V Momentary types

ElecricRatch · Feb 10, 2014

Hi all.

Wondering if you guys can help me.

I'm creating a very simple motorcycle loom and have run into one area where I'm not 100% clear on what to do.

I have a remote triggered relay board which can trigger / switch 4 things.

The board is continuos feed, 12V and 20amp per output.

I have a starter relay for the bike which is clear - the relay will crank the starter as long as the remote relay supplies it - whilst my finger is holding down the remote fob.

However - before I start the bike I must move the bike to 'Ignition' and here is the tricky part.

The bike demands 60amp to supply all loads. So I need to use another relay to do this but I need it to behave like a switch - 1 tap ON - 1 more tap OFF.

I understand this is called a LATCH relay - but I cannot find any latch relays over 25amp.

Any ideas?

tazz · Feb 10, 2014

used a low current latching relay, to feed a high current normal relay.......the latching relay will hold the high current relay on.

ElecricRatch · Feb 10, 2014

Thanks for your reply Taz.

Could the remote relay not do this same job? Thereby negating the low current relay?

ElecricRatch · Feb 10, 2014

Thanks for fast reply.

Could I not use the remote relay to hold the high current relay on? It can deliver 20amps switching current. Though to hold the 60 amp relay on would require less than 1 amp?

Menas I coud do without the intermediate latching relay.

tazz · Feb 10, 2014

the remote relay would need to latch....if it does then fine....relay coils only tend to draw milliamps.
Does sound a bit of a dangerous set up tho....consider the steering lock coming on while driving...!!

ElecricRatch · Feb 10, 2014

Why would the steering lock come on?

1) There is no steering lock.
2) Its a custom - keyless ignition. The top yoke is devoid of any key or switch.

The remote relay is more like a 'switch' rather than a relay. You turn it off or on.
Its operated by bluetooth - the plan is to turn on ignition and the starter motor from my phone - viai a simple app I'm making.

TSRB430- 4 Channel Bluetooth Smartphone Controlled 30A Relay Board with Enclosure

Darkwood · Feb 10, 2014

Im not sure what your trying to do would be street legal .... good luck on getting it insured when you have designed the Electric starting system unless you can provide certification that you meet the relevant standards for safety and design.

I think the initial relay you were looking for is a change-over relay but check its what your after by reading up on it.

tazz · Feb 10, 2014

Ok from information, you posted can see the idea, if you only using 2 relay ie one for starting and on for ignition, could suggest you lock one of the other relays to ignition ie one turns ingition on and locks itself, the other relay the unlocks the ignition relay, so basically the ignition relay is self latching

ElecricRatch · Feb 10, 2014

@Darkwood
its nothing more than a remote start system. Pretty basic and quite common. I'm just using a phone instead of a fob. All the bike requires is an MOT and it is legal - not sure why you deem my loom or circuits as unsafe when I haven't mentioned any detail other than the plans for ignition and start. It will be superior to manufacturer looms in every way with a digital fuse controller and premium components everywhere along with properly fused, terminated, insulated and routed wiring.

I've seen work from 'certified' electricians that would make you wince.

@Tazz
The starter relay is run from a microprocessor controlled fuse controller - which only powers up when the ignition relay is latched to then flow the 60amps it needs. So it cannot start until ignition is on - as normal.

There are of course hidden manual kill and start switches wired in parallel just in case.

tazz · Feb 10, 2014

Do have a good knowledge of electronics, as a pcb designer. limited on micros , but do understand i/o level of micros, with limited C / hex programming.......your have 4 relay outputs, so we can self latch a relay, and release by a second, very basic.....or if you wish, we can use cmos logic to latch an output.

ElecricRatch · Feb 10, 2014

The output of the remote relay is 'continuous' which I take to mean delivers constant current. So it will hold ignition relay ON a make it latched until I switch it off and so it up latches ignition relay.

The starter is a bit more tricky. A starter relay doesn't want constant current - just current whilst the start button is down because for my bike it's upto 80amps. I will have to program app to do timed starter trigger of 3 seconds max or better yet execute 'tactile' current - only when button is held down.

Otherwise the remote relay will fire the starter relay constantly even when engine is running - not good obviously.

ElecricRatch · Feb 10, 2014

tazz said:
Do have a good knowledge of electronics, as a pcb designer. limited on micros , but do understand i/o level of micros, with limited C / hex programming.......your have 4 relay outputs, so we can self latch a relay, and release by a second, very basic.....or if you wish, we can use cmos logic to latch an output.

By the way - the board is not programmable and I think what you describe us not possible via the app controls which are very basic.

Darkwood · Feb 10, 2014

ElecricRatch said:
@Darkwood
its nothing more than a remote start system. Pretty basic and quite common. I'm just using a phone instead of a fob. All the bike requires is an MOT and it is legal - not sure why you deem my loom or circuits as unsafe when I haven't mentioned any detail other than the plans for ignition and start. It will be superior to manufacturer looms in every way with a digital fuse controller and premium components everywhere along with properly fused, terminated, insulated and routed wiring.

I didn't deem them unsafe just an heads up that if you alter anything from its original design you may need to declare it when insuring the bike, it may well pass its MOT but all insurers have clauses and just be careful you read them thoroughly failure to do so may mean you don't get payed out regardless off reason for claim. I insure my van and car and im always asked if ive added to or adapted my vehicles in any way ... if i have i let them know and they decide if its irrelevant or not and may increase or decrease the quote you get.