Dual car batteries, VSRs

RetiredUSNChief

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I've thought a long time about installing a second battery in my car, and over the years with more and more personal electronic devices entering our lives this thought has kept percolating in the back of my mind.

Anybody here have any experience with this, say, with leisure battery systems on RVs, boats, etc?

There are several methods, but the best option for what I want is through the use of a Voltage Sensing Relay (VSR).

They're simple enough. But I've never worked with VSRs for this and am not familiar with which are considered to be quality products.

Right now, Tmax has my attention, specifically their 47-3800 system for around $130, give or take.
 
I did it 22 years ago in a competition car stereo system. I had a manual marine grade battery switch in the car to isolate the "stereo" batteries from the under-hood battery and the alternator. An automatic relay would have been great to have, but manual switches are less likely to fail.
 
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I installed the tmax in my truck with a 2nd battery about 4 years ago. It was fairly straight forward and has function perfectly when my main starter battery has died. No complaints.

This is the basic setup I used to run aux lights.
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I have this bookmarked if I want to do solar panels one day.
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We had dual batts in our passage making vessel, and in the commercial vessels I worked on. After you get 'em hooked up and isolated, you have to consider whether you can charge them properly. If it's a deep cycle lead acid battery, you need to replace your automotive voltage regulator with one capable of three stage charging. (Most automotive alternators have the voltage regulator built in, which is a pain when you add deep cycle batts... gotta find one without a voltage regulator.) Also, an 80A alternator or something similar is a good idea, so that you can charge 'em up at the rate the first stage requires. Also, if you want to charge the batteries without cranking up the engine, you need a charger that plugs into shore power, like golf carts. Keep it in yer garage, and all is fully charged when you crank up in the morning.
 
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I would REALLY like a DC-DC charger, like Redarc makes. Those are SWEET setups for deep cycle batteries.

But I'd be looking at $800, give or take. And that doesn't figure in the cost of a deep cycle battery, either.

I loves me some gizmos, so it's easy to start racking up hundreds more on this.

Honestly, I'll probably end up with something like the Tmax and a standard car battery for the secondary battery, and set up something to warn me when I get down to about 10.6 Volts on it.

It's my car... not a camper or work truck. Most usage would be for phone and laptop charging, which a standard car battery would handle easily.

A deep cycle battery and DC-DC charger would just be a dream setup.

If I DID ever do my dream setup... maybe I'll dig out my old Texas Star 667 linear amp that I burned up so many batteries and alternators with back in the day!
 
Cr*p! Redarc has the DC-DC charger I wad looking at last night for about tree-fiddy... now it's got me thinking about spending more money than I really should again!

I'd like to get their BCDC1225D.
 
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Back in the mid 1980’s I added two batteries to my 1977 GMC Jimmy so as to power a winch. What I learned is that it’s best if all batteries are the same age and type, else one may not charge properly.

I added this type of battery isolator to keep them charged, and a manual rocker switch feeding an RV type solenoid so that I could jump the main vehicle battery off of my secondary bank if desired.

https://www.amazon.com/Cole-Hersee-...words=Battery+Isolator&qid=1584879721&sr=8-10

The only things powered by the secondary battery bank was the winch and some off-road lights. My logic was that if I ran the batteries all the way down using the winch and lights, I still wanted to be able to start the truck and drive it.

I still have this vehicle. It’s had several replacement batteries since then, and one replacement isolator, but otherwise the system is working fine.
 
They make smart splitters, now, which is what makes the Redarc DC-DC charger so attractive. I can run a deep cycle secondary battery and it'll properly charge it with no problem.

I think a Tmax with a standard car battery secondary will do me right, though. I'll consider something more grandiose on my next vehicle.
 
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