VSR's and Solar

[LadyInBed]

When the engine is fired up, how would a VSR react to seeing both battery banks showing 12.8 volts or more from a substantial solar bank
or doesn't it matter as the alternator will attempt to push out current at about 14 volts?

 

[VicS]

When the engine is fired up, how would a VSR react to seeing both battery banks showing 12.8 volts or more from a substantial solar bank
or doesn't it matter as the alternator will attempt to push out current at about 14 volts?

It will almost certainly not react to 12.8 volts
A bidirectional VSR will close when it sees a voltage of more than its specified closing volts at either of its terminals. Perhaps around 13.3 or more. It will open again when the volts falls below the specified opening figure at both inputs. Perhaps around 12.6 volts
A unidirectional VSR only senses the volts on one terminal. Usually the one to which the alternator a priority battery will be connected but it could be wired to sense the battery to wich the solar cahrger is connected

See the Tech data for your VSR for the exact voltages

 

[BabaYaga]

There will be some charge to put back into the starter battery (because of the cranking), but almost at once the voltage will be at the level where the VSR closes. The system voltage will then soon reach the alternator regulator's set point (14,4 V or so). At this point the regulator will begin to cut back on current in order for the voltage to not overshoot 14,4V. Within a few minutes the current will be close to zero, if there are no loads on the system.

 

[Jamie Dundee]

I've got solar to the house battery and a VSR, the VSR allows excess power to the engine battery when the engine is off. With the engine running excess power from the alternator goes into the house battery and the solar controller shuts down the feed from the solar panel.

 

[RupertW]

For some reason I’ve never investigated our alternator tops at 13.3v - which is made getting solar last year more urgent (and then a better alternator if that wasn’t sufficient). The domestic batteries have the MPPT connected and are almost always higher than 13.3 when we start the engine so in that case it works quite well, bringing the engine battery up to 13.3v which is good for its longevity (14 years and going) whilst the domestic batteries keep on going up.

 

[ithet]

I have been meaning to post myself on this issue. One of the things I like about a VSR normally is that the domestic circuit is isolated from the starter until after engine start thus isolating the electronics from any start spike. With the solar providing voltage and holding the VSR shut pre-start I would seem to have lost this protection (Cyrix dual circuit VSR). Would I be better with a single circuit VSR? Does it even matter - the same condition must arise when starting with the mains charger connected?

 

[PaulRainbow]

Vic is correct at 12.8v nothing will happen. I have the Victron figures handy, so let's use those.

<13v nothing happens, but once closed it will stay closed until the voltage drops below 12.8v

So if the solar controller is charging and the above conditions are met, the relay will be closed. Staring the engine may draw some current from the domestic bank, but as the batteries are likely charged this doesn't normally cause any voltage drops that affect electronics etc.

If the voltage is below the above figures the relay will be open. The relay will do nothing as the engine is started, but once the alternator charges it will close shortly thereafter, the time delay depends on the output voltage of the alternator.

Exact voltage set point will vary between different makes of relay, but the principal remains the same.