Greetings all from Oregon, where we kiss where the sun don't shine.

'Easy Bake' the '81 black panel E 150 I have was set up with a dual battery system over a decade ago by me using an isolator I got from EBay, circuit breaker mounted above 2nd battery and 6 gauge wiring.

Since about 8 months ago when I occasionally startup and drive this rig I notice the voltmeter is bottomed for a few seconds and the ammeter is showing charge (10-12 amps) more than normal. I hear the new belts squeal and then after 5 or 10 seconds all is well. The alternator I replaced a few years back with a high amp output Ford unit from Autozone.

I've run smart chargers on both batteries when I'm out and about in my other rig and this seems to take care of the problem for a few days. The secondary battery seems to be the culprit as it's the older of the two but I'm only driving audio and 11 meter radio gear with it, and it is key switched.

After changing belts, checking connections for oxidation, verifying battery (distilled) water levels I'm reaching my wits end. Perhaps the isolator is to blame, or the alternator? I don't know.

Here's a few pics of my battery system;


The primary battery


Primary battery with caps removed


The secondary battery


The isolator


The circuit breaker

 

Batteries do get old and start getting weak. That battery sounds like it's sitting and discharging, and then is demanding a lot of current after the engine starts. Do you have another battery laying around that you could swap in?

 

I'd recommend two things. First, as Dave pointed out, batteries do age and eventually self discharge and place a load on the charging system. Pull the battery and take it down to your local auto store and have them test it. Have them do a test using a real conductance tester like a Midtronics, not just a toaster style tester. That will tell you the real condition of the battery.

The second recommendation is to do away with the isolator and replace it with an automatic battery combiner (ACR). The diode style isolator has approximately 1 volt drop across the terminals so your battery is perceptually undercharged which isn't good for its longevity. ACRs are made by a variety of companies but the ones I'm most familiar with are the Blue Sea units such as the https://www.bluesea.com/products/761...12_24V_DC_120A. They also make a 500 amp unit if you have a high amperage alternator installed.

 

Never seen one of those before. Sort of a "smart relay".

 

My normal use for them is in customer's boats to simplify charging. It helps to keep them from brain farting and discharging all their batteries because they forgot to change the battery switch after shutting down the engine. They also have a start interrupt lead which can be wired into the solenoid energizing lead which causes the ACR to open so that starting current doesn't get passed through the ACR to the other battery.

 

Hmmm not familiar with the term ACR, but in my other rig I run a SPG 32 (not to be confused with SPG ((Special Patrol Group)) of Vivians pet hamster of "The Young Ones" fame) that resembles a starter relay.



I wonder if this is one of those critters. On the other hand, since I'm short of time and money my practice has been when I swap out the primary battery,I test the electrlitics and bring it to full charge I've moved 'em to the secondary position. Again, it's not under heavy load, like driving an electric winch or something. Further I'm not a motormouth on the radio despite the tuned radio and 250w brick I have attached to the seat nor is there any large or constant current draw of the radio (11 meter or double amped audio gear). So I can't imagine why the system is flagging like this. Perhaps when I get money up I'll buy a new battery, but times are tight as I just paid my quarterlies.

 

An Automatic Combiner Relay (ACR) is like a smart battery switch. If it sees charge level voltage on either terminal is closes. Once battery voltage drops below 12.6 volts it opens. There is a little smarts in there to keep it from chattering and stuff like that, but otherwise they're really simple stuff.

 

How about that? and I thought that's just what the isolators accomplished. Be it known though that this system in place has worked well for over a decade and it's only been of late that this issue has surfaced which leads me to believe that this is due to some sort of breakdown rather than design flaw.

 

The problem with normal isolators is that they use diodes to accomplish the task. Depending in the quality of the components there is anywhere from a 0.7 to 1.2 volt drop across the isolator. This leads to a perpetual undercharging of the batteries, as well as slower recharge time for house battery. Yes, it works, but then again non-synchro transmissions also work. ACRs are just a more efficient better quality means of solving the same problem.

 

The diode isolators do fail.
The one you have doesn't look like a schottky diode isolator so will, as mentioned, create excessive voltage drop which will eventually kill your batteries. This can be corrected by using an alternator with an adjustable voltage regulator and upping the charging voltage.
Schottky diode isolators don't cause as much volt drop, about 0.5v.

IIRC ACR's would handle combining different types of batteries and are definitely cheaper than Schottky isolators.

 

Neither diode isolated, Schottky or otherwise, nor ACRs should be used to connect battery banks of dissimilar battery chemistry. That said, the differences between lead acid and most AGM batteries are little enough that they can be treated the same with some caveats. The biggest exception is that of the bulk charge acceptance rate, and that generally applies to deep cycle batteries, not starting batteries.

Rereading the First post I noticed that both batteries are starting batteries. The OP would be better off using a deep cycle type battery for the secondary battery. They are designed to be more deeply discharged and the withstand the discharge/charge cycle better. Get the secondary battery tested. I think you'll find it's time for replacement. Then replace it with a quality true deep cycle battery. Don't use a dual purpose.

 

Yes, I read up on the difference between the deep cycle and the starting automotive batteries a long time ago. The jist I got if anyone wants a short explanation;

Starting battery is for short duration very high discharge rates. The plates inside these batteries are delicate honeycomb structures that expose more lead surface area to the acid. This gives the capability of very high output for the high current draw of the starter. The problem I read is deep discharging and re-charging can damage this delicate plate structure.

The deep cycle battery is built different inside. Very thick heavy duty plates. They can withstand deep discharges and re-charges without damage. But they cannot supply the very heavy amperage a starter needs in the same small package. They do not have the same plate exposure per square inch like a starting battery.

 

Thanks guys for your concise information. After getting the hold down hardware and cabling clear from the data plate I see it's 10 years old slightly exceeding service life.