The circuit loss is due to the relatively large current [Amps] drawn by the solenoid coil. You will be feeding this coil thru the closed relay. Your IG switch circuit will only see the small current the relay coil draws [fractional Amps]. Thus the relay coil will see full OCV [>12] until the starter kicks and pulls the whole system down a V or so. So no problem with activating or holding Voltage.
Youve introduced lots of confusing factors without saying anything wrong. ... The succinct point is that you dont lose voltage thru contacts and wiring that is not carrying current. And the current to the relay coil is very low.It is not exactly clear to me what you are trying to express...but when you say there is "no problem with activating or holding Voltage." I can tell you that this portion of your statement is denied both by electrical theory and practical experience of members here at TBN.
Specifically, a relay coil that is activated through a series string of contacts, whatever those contacts may be, will have a voltage impressed across its operating coil that is equal to the value of the voltage applied to the circuit, MINUS the voltage drop across each contact that is in the series string. This is fact not fiction.
Historically, in the archives here over the past ten years or so, there have been multiple posts regarding the starter motor solenoid just clicking and NOT pulling in enough physically to engage the starter motor. The reported final cure has been to install a relay that will pick up at lower voltage than the factory equipment, to be activated by the circuit that originally was hooked to the starter solenoid terminal. This is the one in the JD kit. (but as I think you may be saying, different relays that pull lower current may also work) Then contacts from this new relay were inserted directly between the battery terminal on the starter, and the starter solenoid terminal. This way full battery voltage was applied to the starter solenoid terminal when the ignition switch was turned to the start position( provided that all permissive contacts in the safety circuit were closed).
The relatively large current that you refer to I assume is that required by the starter motor solenoid. This high current is what causes relatively large voltage drop to develop across contacts in the safety circuit that have deteriorated somewhat over time. The new relay requires less current that the starter solenoid for proper operation. Therefore there is relatively less voltage drop lost across contacts in the safety circuit, and a greater percentage of applied voltage is felt across the relay coil. Any 12 VDC relay that draws less current than the starter motor solenoid may work. Having a coil rated at 12 VDC that will operate at 7.2 VDC gives an even greater margin or error to the benefit of proper operation. Of course the power circuit, between the battery terminal of the starter motor and the starter motor solenoid, in both cases will have only ONE contact in use.
It is that simple. Any relay that operates at 12 may work; one that works between 7 and 12 volts can only be better in the long run.
Spyderlk, I am not sure if you are saying that any 12 volt relay would work for this modification; there certainly is a chance this could be the case, at least in some instances. A new small relay would likely draw less current than the starter motor solenoid does. Less current through the safety circuit would result in less voltage drop across the problem contacts.
However, a relay coil that both draws less current AND activates at a voltage significantly less than the 12 VDC battery voltage will always be superior in this application, especially since contacts that have increased there resistance over time will likely continue to worsen.
This post is an attempt to ensure that the reasoning behind this proven fix is reviewed (if anyone cares to). I installed the JD relay in my BX2200 yesterday and it works perfectly. No more "Click, click, click....start!" I am expecting this to be the case even as the safety circuit contacts worsen.
If I had a suitable standard 12 VDC relay on hand to use in this application I probably would have tried that first. Why not, the price would be right and it might be enough to do the job. But since I did not I decided to maximize my odds over the long run, and buy a relay that offered greater potential long term benefit...
It is not exactly clear to me what you are trying to express...but when you say there is "no problem with activating or holding Voltage." I can tell you that this portion of your statement is denied both by electrical theory and practical experience of members here at TBN.
Specifically, a relay coil that is activated through a series string of contacts, whatever those contacts may be, will have a voltage impressed across its operating coil that is equal to the value of the voltage applied to the circuit, MINUS the voltage drop across each contact that is in the series string. This is fact not fiction.
Historically, in the archives here over the past ten years or so, there have been multiple posts regarding the starter motor solenoid just clicking and NOT pulling in enough physically to engage the starter motor. The reported final cure has been to install a relay that will pick up at lower voltage than the factory equipment, to be activated by the circuit that originally was hooked to the starter solenoid terminal. This is the one in the JD kit. (but as I think you may be saying, different relays that pull lower current may also work) Then contacts from this new relay were inserted directly between the battery terminal on the starter, and the starter solenoid terminal. This way full battery voltage was applied to the starter solenoid terminal when the ignition switch was turned to the start position( provided that all permissive contacts in the safety circuit were closed).
The relatively large current that you refer to I assume is that required by the starter motor solenoid. This high current is what causes relatively large voltage drop to develop across contacts in the safety circuit that have deteriorated somewhat over time. The new relay requires less current that the starter solenoid for proper operation. Therefore there is relatively less voltage drop lost across contacts in the safety circuit, and a greater percentage of applied voltage is felt across the relay coil. Any 12 VDC relay that draws less current than the starter motor solenoid may work. Having a coil rated at 12 VDC that will operate at 7.2 VDC gives an even greater margin or error to the benefit of proper operation. Of course the power circuit, between the battery terminal of the starter motor and the starter motor solenoid, in both cases will have only ONE contact in use.
It is that simple. Any relay that operates at 12 may work; one that works between 7 and 12 volts can only be better in the long run.
Spyderlk, I am not sure if you are saying that any 12 volt relay would work for this modification; there certainly is a chance this could be the case, at least in some instances. A new small relay would likely draw less current than the starter motor solenoid does. Less current through the safety circuit would result in less voltage drop across the problem contacts.
However, a relay coil that both draws less current AND activates at a voltage significantly less than the 12 VDC battery voltage will always be superior in this application, especially since contacts that have increased there resistance over time will likely continue to worsen.
This post is an attempt to ensure that the reasoning behind this proven fix is reviewed (if anyone cares to). I installed the JD relay in my BX2200 yesterday and it works perfectly. No more "Click, click, click....start!" I am expecting this to be the case even as the safety circuit contacts worsen.
If I had a suitable standard 12 VDC relay on hand to use in this application I probably would have tried that first. Why not, the price would be right and it might be enough to do the job. But since I did not I decided to maximize my odds over the long run, and buy a relay that offered greater potential long term benefit...
SPYDERLK said:
I have highlighted and emphasized the part of my true quote that likens the relay activation circuit to a near "zero" current case. That established it follows thru orderly thought that such [high activation impedance] relay capable of pulling in at well below 12V has no added value in this case. Its OK that it can ... and could be critical in a different circuit situation - just not of any real benefit here.