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After dealing with some charging system trouble, I believe I have identified the malfunction's cause and an effective remedy for it, one which can be prospectively applied to avoid the problem. I'm publishing this because it should be of general interest to V-Strom (or other bike) owners.

The first symptom was a starting failure -- the engine turning over maybe once and then no more on that battery charge. For those without a voltmeter hooked up, this will often be the initial indication of a problem with the stator, rotating magnets, or the regulator.

I'll condense the days-long, involved diagnosis process which would likely only interest electrical engineers in detail. In short: The regulator seemed to be establishing an equilibrium battery voltage which was much closer to the end of its discharge curve, (voltage versus removed charge or versus time at constant current), than to the curve's well-charged end. The AC input to the regulator was fine; it just would not allow enough power to reach the battery to get it charged. This I deduced from observations of battery voltage under various conditions: just after a start; with 0 or 2 headlights powered; after running over 3K RPM for awhile; after recharge with an external charger; and combinations thereof.

I ordered a Shindengen SH775 regulator as soon as it became apparent that the original (stock) regulator's voltage setpoint had become too low. In preparation for the wiring futzing which will be necessary to install the new regulator, I pulled the old one to look at it, then remounted it so I could ride the bike further between sessions on the battery tender.

The simple act of moving the regulator output connector pins effected a significant increase in equilibrium charging voltage observable at the battery. Seeing that was what finally struck me with insight as to what had really gone wrong. The stock regulator's voltage setpoint, as observed at its own output, upstream of its connection to the DC bus, is fine. Sadly, the cheap, non-noble metal pins in the connector have suffered the gradual increase in contact resistance which motivates people who seriously intend a long-lived connection to use noble metal plating at the contacting surfaces.

The effect of moderate contact resistance increase at the regulator output connector is to drop the (poorly) "regulated" bus voltage by an amount equal to the product of the load current and the sum of both resistances (+13 & return). This resistance increase is a regenerative phenomenon -- as I^2*R loss at the contact goes up, thermally induced motion goes up which increases the rate at which oxide grows into the interface between the contact faces.

When (or if) I design a replacement regulator, it will have either noble metal connector pins for the output or an extra pair of sense pins so that battery voltage can be regulated rather than the pushed-onto-cheap-connector voltage.

The quick cure (or temporary alleviation) of the problem is to clean up the regulator output connector pins and squeeze them closed a little more to improve contact pressure. (Pressure helps resist incursion of oxide between the contacting faces.) The need for this can be deduced from drop in the battery voltage seen after the post-start recharge transient has settled out. There is no need to wait for it to drop low enough to risk the grief attending a starting failure.
 

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The quick cure (or temporary alleviation) of the problem is to clean up the regulator output connector pins and squeeze them closed a little more to improve contact pressure. (Pressure helps resist incursion of oxide between the contacting faces.) The need for this can be deduced from drop in the battery voltage seen after the post-start recharge transient has settled out. There is no need to wait for it to drop low enough to risk the grief attending a starting failure.

or you could prevent oxidization by using a product like DeOxit dielectric grease

when I had my new wire harness installed, I have my dealer carefully coat the pins in every connection with DeOxit conductive grease or non conductive grease depending on the risk of creating a short between pins



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That's one reason why switching regulator/rectifiers carries the additional recommendation to run the DC wires directly to the battery. DeOxit or ACF50 on all connectors helps too. Remember that SH775 also has connectors on its body.
 

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I have a Shindengen SH775 sitting here waiting to be installed by me, so do I have to do anything with those connectors?
 

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Discussion Starter #5
I have a Shindengen SH775 sitting here waiting to be installed by me, so do I have to do anything with those connectors?
Something to forestall oxide formation at the contacting surfaces is an excellent step. Something like DeoxIT.

I plan to bypass connectors on the regulator output entirely, in favor of soldered connections, once I've established that the new regulator is working correctly.

And a permanently connected voltmeter seems like a compelling improvement now. I've gotten weary of charging system failures appearing by surprise.
 
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