Solar and VSR relays

[Camavenah]

Hi this is my first post I’m interested in vehicle solar installation,
My solar set up is as follows was wondering if all sounds ok???
During sunlight

voltage at leisure battery showing 13.3v
140A Durite VSR closed (LED illuminated)
voltage at starter battery showing 13.3v
Now obviously the 2 batteries will show same voltage as when relay closed they are connected in parallel. So this now makes sense.
I mistakenly thought that the VSR would only sense voltage from one direction but it appears that it senses from either the in or out (SB or LB)
There fore if the solar is above 13.3 v (which it is in direct sunlight) then the VSR will remain closed. My only question would then be is there any issues that when I start van that current will be drawn, if only momentarily from both batteries? Also do anybody know of a VSR relay which only senses voltage from one direction??
I’ve also attached a pic of my set up. Cheers for the reply

[ajriding]

I see that your needs are different. I notice most people close and lock the truck when camping, but everyone is different...

The solar charge controller will sense exactly what the battery needs, and do this several times per second, in order to deliver the perfect amount of voltage to the battery to optimize charging. It will work with a bank of different batteries, but the controller is now sensing what the bank needs, not what the individual battery needs, so having different controllers would mean that each battery gets its own attention and specific charge rate, not just a general charge. This is a minute detail for the traveler who just does a few trips, but for a full-timer or part-timer would be much more significant.

I am personally weary of using any power from the starting battery to power the coach, even if it disconnects at 13 volts. A starting battery cannot cycle (charge and depleated a little over and over) as many times as a marine battery, and a marine not as many as a deep cycle, so keeping the starting battery only for starting the motor will extend its life. Again, it will work, and for infrequent camping trips will not really matter so much.

I understand using your trucks accessories as part of the camping experience, even the radio...
On my first motorhome (could work for a trailer or TC also) I actually pulled DC power from the coach battery for a few things: the radio and the captains drivers seat ran off the coach battery. The radio did because I could use the door speakers and hear them in the camper just fine and wanted to save the starting battery (phantom power still came off the vehicle). The captain's chair because it was just easier to pull the power from the coach battery, which was behind the chair area, than pulling off the vehicle (the alternator always charged coach batteries when driving, so it was really the same as pulling from the vehicle here).

Good luck on your adventures.

[KD4UPL]

I will respectfully disagree with the last poster. I don't think it's strange at all. In fact, I have basically the same set up on my truck and TC. When parked at a camp ground frequent opening of the truck doors triggers the dome lights. Do does using the truck's radio or in my case ham radios that were wired to the truck. I liked the fact that my camper converter or solar panels were keeping my starting batteries topped off.
The camper can't drain the starting battery as you fear. When the voltage gets below around 13 volts the voltage sensing relay disconnects the batteries.
My starting batteries and RV batteries were both flooded lead acid, same chemistry. While technically not an ideal combination to charge in parallel the charging requirements are basically the same. I had no problems in many years.

[ajriding]

This is a strange set-up.
No, there is no problem for the starter to be attached to both batteries if both are good. If the coach battery (leisure) is low, then that could possibly pull enough amps out of the starting battery to not start the motor (just depends on a few factors).

Curious, why do you need to put solar on the starting battery? Is it stored for long periods of time? If not stored, then the starting batt really does not need solar. If stored, then it is better for the batteries to each have its own charge controller. You are charging a starting battery and a marine battery, two different types, from one source. The chargers are smart, but there will be confusion from mixing batts.

A 20 watt solar panel is plenty to keep starting battery topped off for storage, and a $19 controller will do the job.

The relay is to disconnect the batteries when the alternator is not charging, this keeps one from draining the other battery, so you can start motor even when the coach batt has been run dead. Usually the relay has a switch connected to the ignition so when the starter is turning the relay disconnects the two batteries from each other. You notice your radio turns off when you crank the motor, the same will happen on the relay, it will turn off (disconnect the two batteries).

I would discourage charging both batteries from one solar source.
I would install a switch to manually turn on/off your relay from the vehicle alternator to the coach battery. With solar you might not need the alternator very often. The alternator is not as good of a charger than the smart solar controller, though the alternator does has the sheer power in amps to do the job quick, so if batts are dead, do a couple hrs charge to get them near full, then let the solar take over for the final few percentages (I dont know how you would know when to do this though).

With more info I might can have more advice if this is of interest

[ndrorder]

Not a problem drawing current from both batteries during startup. The starter will only draw the amperage it needs from the path of least resistance which is typically the starter battery. Many rvs have a switch to close the vsr so the leisure battery can help starter battery if needed.

There are different systems to perform the task of the vsr. They use a non-sensing isolation relay controlled by either a bidirectional isolator relay delay (bird) or an isolator relay delay (ird) that sense voltage from both or single direction, respectively.