Bosch relay connections
Thread Starter
|
Member
Joined: Mar 2001
Posts: 40
Likes: 0
Bosch relay connections
for pins 86 and 85 does it matter which one is grounded and which one has the voltage on it? my impression is that it makes no difference. gonna hook up my illumination this weekend. yay!
Always be prepared 
Senior Member
Joined: Sep 2000
Posts: 1,704
Likes: 0
From: Mpls, MN
I've wired several relays in the past and always used the terminals the instructions stated. Never thought about doing it differently.
I think it actually does matter which posts are used. I'm not sure about the relay you have there but I did open up the Bosch starter relay on my motorcycle when it burned out and there are a number of Capasitors and Resistors in there connected to different posts.
-Adam
I think it actually does matter which posts are used. I'm not sure about the relay you have there but I did open up the Bosch starter relay on my motorcycle when it burned out and there are a number of Capasitors and Resistors in there connected to different posts.
-Adam
Senior Member
Joined: May 2001
Posts: 157
Likes: 0
From: Wentzville, MO
AJRagno,
Shouldn't the wire coming from the switch in the second picture be going to the 86 post since it is the grounding terminal and put the 12v lead on post 85 since it is the switch terminal that uses +voltage to activate the relay. Your pic shows +volts comming out of a switch that is grounded. I think it should be the same as your first pic but just have the switch between post 86 and ground?
I have been wrong once before.
Let me know
Shouldn't the wire coming from the switch in the second picture be going to the 86 post since it is the grounding terminal and put the 12v lead on post 85 since it is the switch terminal that uses +voltage to activate the relay. Your pic shows +volts comming out of a switch that is grounded. I think it should be the same as your first pic but just have the switch between post 86 and ground?
I have been wrong once before.
Let me know
Last edited by phildacf150; Jul 8, 2001 at 11:30 AM.
Trending Topics
Senior Member
Joined: Sep 2000
Posts: 1,704
Likes: 0
From: Mpls, MN
phildacf150,
Sometimes it makes my brain hurt when I try to understand why something is wired a certain way when there are any number of options. I rewire guitars and amplifiers on a regular basis and it makes a major difference in functionality/reliability.
When it comes to a light relay, such as that we are discussing, terminals #85 & #86 [can] be wired either way but there are potential problems if you're not sure what's inside the relay.
Most relays have a DIODE running between terminals #85 & #86 and since a diode's resistance is directional, if the circuit is active too long in the wrong direction then the diode melts and the circuit either cannot be turned on or it cannot be turned off. I suspect that in the lower drawing there is not a diode in the relay. Turning the toggle swith on completes the circuit in both drawings. It just does it in a different way.
When it comes to a relay, at least for auxilary lighting, I have personally only seen the "Power to turn on circuit" used. (Top Illistration)
-Adam
***Sorry I took so long to reply. I've been away since Sunday morning.***
Sometimes it makes my brain hurt when I try to understand why something is wired a certain way when there are any number of options. I rewire guitars and amplifiers on a regular basis and it makes a major difference in functionality/reliability.
When it comes to a light relay, such as that we are discussing, terminals #85 & #86 [can] be wired either way but there are potential problems if you're not sure what's inside the relay.
Most relays have a DIODE running between terminals #85 & #86 and since a diode's resistance is directional, if the circuit is active too long in the wrong direction then the diode melts and the circuit either cannot be turned on or it cannot be turned off. I suspect that in the lower drawing there is not a diode in the relay. Turning the toggle swith on completes the circuit in both drawings. It just does it in a different way.
When it comes to a relay, at least for auxilary lighting, I have personally only seen the "Power to turn on circuit" used. (Top Illistration)
-Adam
***Sorry I took so long to reply. I've been away since Sunday morning.***
Senior Member
Joined: Aug 2000
Posts: 243
Likes: 0
From: Palm Beach County, FL
Gentlemen,
(AjR, I disagree that most of these automotive style relays have diodes INSIDE as you suggest)
These generic automotive style relays are not polarized and can be activated by switching either the positive voltage or ground on either pin 85 or 86. Thus the difference in the two drawings is mostly semantics.
Either way the circuit is completed, the relay coil energizes, draws the contacts together and completes some other external circuit (and opens another if it has the 87a terminal). If they had diodes inside then they would be polarized and require proper hook-up polarity on those two pins to activate (and would be so identified).
FYI: a diode across a relay's coil (85 & 86 in this example) is there to protect digital output circuits (such as with a microcontroller). When a relay coil is de-energized, the collapsing magnetic field can create a large reverse polarity "spike" that can damage the controlling device's output. The diode, called a "clamping diode", shunts that reverse polarity spike to ground thus protecting the controller.
When using these relays in our trucks to control lights or other non-polarized loads, and properly fused, it is nearly impossible to damage them or the load. If wired incorrectly it simply just wont work.
(AjR, I disagree that most of these automotive style relays have diodes INSIDE as you suggest)
These generic automotive style relays are not polarized and can be activated by switching either the positive voltage or ground on either pin 85 or 86. Thus the difference in the two drawings is mostly semantics.
Either way the circuit is completed, the relay coil energizes, draws the contacts together and completes some other external circuit (and opens another if it has the 87a terminal). If they had diodes inside then they would be polarized and require proper hook-up polarity on those two pins to activate (and would be so identified).
FYI: a diode across a relay's coil (85 & 86 in this example) is there to protect digital output circuits (such as with a microcontroller). When a relay coil is de-energized, the collapsing magnetic field can create a large reverse polarity "spike" that can damage the controlling device's output. The diode, called a "clamping diode", shunts that reverse polarity spike to ground thus protecting the controller.
When using these relays in our trucks to control lights or other non-polarized loads, and properly fused, it is nearly impossible to damage them or the load. If wired incorrectly it simply just wont work.
Senior Member
Joined: Sep 2000
Posts: 231
Likes: 0
From: WustaMass, Where we pahk ah cahs!
Go to www.designtech-intl.com Then create a free account. Once you've logged on, go to the "Tech Tips & Information" section, Document #111, Basics of using 30 amp Bosch Style Relays will provide you with all the info you need for installing relays. Good luck, 
ennis
ennis