Bad experience with Powerstream "Smart" relay for battery isolation

[John Demarrais]

Getting my 1988 Toyota Minicruiser ready for a trip.  The OEM rectifier-based isolator was bad.   I removed it and wired in a low-draw, 150 amp relay along with some #2 copper cable that runs from the front to the back.  My other RV has a relay for isolation but is wired to the ignition circuit.  So when the IGN is "on" -the cranking battery and house battery are hooked together in parallel. When the key is "off" they are isolated.  Works well enough but . . . I don't like all batteries charging at once when I first start.   

So - I got a so-called "Smart" relay-controller from Powerstream.  Several companies sell them.  Main idea is - they sense the voltage of the cranking battery and keep it isolated from the "house" until it gets fully charged first.  Once it gets to 13.5 volts - it closes the relay and starts charging the "house" battery.  Sounds great in theory?    I have the same setup on my Chinook and it works great BUT it's a different brand (Cole Hersee).  I chose Powerstream this time mainly because they will sell you just the control module if wanted. Since I already had a relay - that was my choice. 

Here's the problem.  I installed it last week. I later discovered that once I start the engine -and it closes the relay - it won't turn the relay back off when I turn the engine off. I assumed I had a defective unit -but I was wrong.  Just has bad engineering (in my opinion).  I called the company to verify. Seems that unlike the other "Smart relays" on the market . . Powerstream set their's to shut off at 12.6 volts.  That makes NO sense to me at all.  The tech guy I spoke with seemed to agree with me.   Note that a fully charged battery at rest is 12.7 volts.  That means this "Smart relay" will not turn off the relay until that batteries get run down a bit.  Mine was on for 4 days and still had not shut off.   Keep in mind that once the relay is engaged - both batteries, front and back are tied together.  So there are two fully charged batteries that must be run down a bit before they become isolated. Somewhere around a 95% charge before it shuts down. Like I said . . . mine was on for 4 days straight until I got disgusted and disconnected it.

[Lakota Wolf]

Thats some great info John. I think I had the same problem you just explained. I had the isolator on Ole Red (diesel) and the isolator will let both batteries draw at same time and NOT kick off till below voltage level.

I have sinse changed mine to a marine apllication battery isolator and seems to work flawlessly.

I used the old shade tree mechanic technique and had a volt meter on each battery and had engine running and watched both meters after I started the truck. Showed one battery charging, the other not (but showing full charge), then vice versa after shutting off truck and leaving lights on etc to draw down the batteries,the restarting. (taking into concideration the voltage regulator in Alternator was doing its job). I was monitoring the output voltage to each battery off the isolator and it switched flawlessly.

I have an isolator off my solar panels going to 4 batteries, I still havent figured out how that works, but all batteries seem to be same voltage.

[John "T" Nordhoff]

NOPE doesn't make a lot of sense to me, but I'm more into Electrical then Electronics gadgets...

Being a long time avid RV user I would NOT like the engine battery to remain connected to the house batteries once the engine was stopped and the alternator no longer charging. On my time delay isolation relay system the instant the engine is stopped the relay opens. I don't like the idea of the engine battery still in use until such time its voltage drops.

My RV uses a simple timer. The house battery bank sits there isolated via a normally open relay. When the RV starts (which initially drops engine battery voltage a bit) the relay remains open UNTIL THE PASSAGE OF A TIME DELAY only after which it latches in and connects the engine battery to the house battery bank so the alternator charges all batteries while driving. It gives all the alternators output to the engine battery alone for a short time to replenish it a bit prior to the engine and house batteries all being connected together.

There is one thing worth mentioning. The house battery bank consists of True 6 Volt Deep Cycle Flooded Lead Acid batteries in series/parallel, while the engine cranking battery is a regular truck/automotive lead acid starting battery. After a period of driving the battery voltage (Engine in parallel with house) stabilizes in the 13.9 to 14.2 or so volt range. However and even if you were to drive 6 hours with all the batteries at 14+ volts. IF YOU GET TO AN RV PARK AND TURN ON THE XANTREX TRUECHARGE2 SMART CHARGER it reacts almost like the deep cycle bank is somewhat discharged???? i.e. it ramps way up to near a max charge level for a time before it settles in and then maintains the lower float voltage of around 13.1 to 13.2 volts. Its like the alternator wasn't actually pumping much charge to the house battery bank even though it was connected to the alternator for 6 hours and a voltmeter on the house bank showed it from 13.9 to 14+.

Sounds like a fairly easy time delay relay fix unless you choose to just leave it as is??

John T

[John Demarrais]

Getting ready for a trip. I stuck a disconnect switch on it for now.  Note I've got another RV with a different brand "smart" isolator that works fine.  That one is sold by Surepower and is set to shut off at 12.8 volts.   The reason why I chose Powerstream this time is this. I already have a bunch of new, high amp, low draw, continous-rated relays I got wholesale for $10 each.  Powerstream is the only place I know of that will sell just the control module instead of an entire assembly.  Costs around $25 so I gave it a try. Would be great if set at 12.8 or 12.9 volts instead of 12.6.  My relay was for 4 full days -drawing 9/10ths of an amp for 96 hours. After that 4 days my battery voltage was still 12.72 volts.  I may of started the rig a few times while working on it so there might of been some recharge. Still - it makes no sense to me at all.  When engaged - all the batteries are tied together and it will not disconnect until they are 5% discharged! 

I can see how a time would work nice.  On my diesel RV - I've had a simple setup for years with a relay energized by the IGN circuit. Not perfect though.   Take this situation . ; ;   Do a cold start in the morning.  Glow plugs draw 80 amps for 14 seconds. Then the starter draws 300 amps for 5-10 seconds. That alone is a bit of a recharged demand.  Now -if the rear "house" batteries are worn down - that is a HUGE demand for that alternator.  I've got a disconnect switch on the dash and if I remember - I turn off the rear charge until the engine runs a bit.

 For $25 I thought this module would be a nice feature.  Now I think not.   The module that Cole Hersee and Surepower use - looks much better since they shut off at 12.8 volts instead of 12.6.  The module I got from Powerstream is made by Manson. I attached some specs.