How to safely run a flooded and AGM battery together

[Gnarlodious]

I succeeded in safely running an AGM battery up front with a flooded battery in back. This because the diesel engine likes to have the ready power of a flooded battery, especially important at the high elevation of Santa Fe and in winter. This solution uses a $12 electronic board available on eBay: “EAZY 12VDC controller”. The device I used had the eBay title of “12V Voltage Control /Delay Switch /OverVoltage /Under Voltage Protection Module”. It basically overrides the Yandina battery combiner relay when the charging voltage is higher than 13.6 volts. When the charger switches down to AGM float voltage, which is lower than 13.6v, the controller releases control of the Yandina. The system is completely automatic and works well. I made an exhaustive video that explains how to use the EAZY V2.3 Voltage Controller to prevent overcharging a flooded battery while charging an AGM. It disconnects the lead-acid flooded battery when the AGM is charging more than 14 volts:

Link

The video shows why it is necessary, how it operates when overriding the isolator relay, how to program the device for this configuration, and how to wire the device. Programming instructions start about 8 minutes in.

Ideal mode for this device is P-5. Mode P-5 includes mode P-4, which is an overvoltage controller, along with mode P-1, which is a time delay function. The device is set to turn off the Yandina at 14.2 volts or above. The controller releases the Yandina at 13.6v or below, at which time the P-1 delay activates before allowing the Yandina to go into automatic mode. The Yandina relay uses the green wire, which when grounded disables relay action. No power leaves it on automatic. An on-board relay on the controller board is wired so that when it is energized, it grounds the green wire.

This solution can be used on any isolator-combiner relay such as the “Blue Seas” unit. In fact, if I had known about this cheap and highly configurable controller I would have employed a generic relay with a controller on either side.

Green LED glows when the on-board relay is energized.
Default setting is that the relay is OFF when upper limit is exceeded. This means that during normal charging the light is ON, which is a little irritating. To reverse the relay logic, when you first select mode 4, then press ENTER, hold the SET button down for 3 seconds, then release it. This makes the light come ON while the AGM is charging on high voltage. If your charger is under the seat like mine is, this gives you a convenient way to visibly monitor its high voltage output. The voltmeter display can be disabled in mode P-8.

Mode P-5, time delay activation, is necessary because of the smartcharger's behavior (applies to the ProMariner ProSport charger) wherein it momentarily pauses its charging periodically, like maybe every 2 minutes. I presume it does this to measure the quiescent voltage of whatever its charging. Apparently this only happens when recovering from a deep discharge, I have not seen it happen on a shallow charge. If it sees a low voltage it continues charging at maximum current. If it sees a high voltage it stops checking. Mode P-5, as I have set it, inserts a 10 second delay before energizing the on-board relay, thus preventing annoying oscillation. Its possible other AGM chargers would not have this behavior and the simpler P-4 mode would suffice.

Each installation may find custom settings are needed. When recovering from a deep discharge, the auxiliary AGM battery will absorb enough power to drop the maximum 15v charging voltage to an unknown low level. This "lowest anticipated voltage" may vary according to battery brand, other loads on the system, charger characteristics, and ambient temperature. These variables may take an entire year to work out, depending on your camping lifestyle. Meanwhile, you need to monitor the voltage at which the Yandina relay engages, because it could conceivable energize at some low voltage but while the charger is still in ‘recovery’ mode. This could cause the cranking battery to overcharge indefinitely, since the smart charger will never kick down to float mode while it is overcharging a flooded battery. I will update this discussion when I figure out how the system behaves under more extreme circumstances.

This setup has been a real breakthrough for me, I hope it helps someone else.

Addenda:
I had to set the upper voltage to 14.2 volts, 2/10v above the maximum voltage the alternator charges when both batteries are charged. Under that condition, the alternator would exceed the set voltage of 14v, causing a slow oscillation of the Yandina. Problem solved.
_________________
Vanagon ’83 diesel AAZ w/Giles injection, 5spd 4.57R&P+TBD and a '78 diesel Rabbit

[fxr]

Thank you for that - very interesting find, could be very useful. I hope you add any further observations.
_________________
Jim Crowther
1984 1.9l EJ22 Westy Wolfsburg Edition
Vespa GTS 300

[VeeDubDaySpa]

How has this held up over the past year??
_________________
North American Hightop Installer/Distributor
Current stock (3)
Hot Water Systems
_______________________________________
90 Syncro NAHT Vanagon RHINO
86 "Syncro" Van DIAMOND
87 Syncro Hightop WestyCamper ROCKY (for sale soon)
79 bay window OLIVER

[Gnarlodious]

Working real good. When running on alternator, the relay cycles off and on a little more than I’d prefer. Its tricky getting the exact hysteresis set. But its working as expected, and my batteries are healthy!
_________________
Vanagon ’83 diesel AAZ w/Giles injection, 5spd 4.57R&P+TBD and a '78 diesel Rabbit