Battery protection

Maine Sail · Mar 7, 2019

kbata22 said:
I have a High output alternator with an external voltage regulator and two 12v AGM batteries. A few years ago I was motoring for a while, then shut down the engine for a while. When I tried to start the engine I had nothing. I went to look in the battery compartment and the cover was warm. The batteries were fried. The external voltage regulator had failed and the unregulated alternator fried the batteries.
Does anyone know if theres a simple way to protect the batteries in the event that this happens again? Maybe a high voltage audio alarm or something that would automatically disconnect the alternator.

If an external regulator fails it normally just stops working because the field is lost. You can't have run-away voltage without field voltage/current. We've not once seen a Balmar voltage regulator fail in that fashion where field is operational but the voltage runs away. Could it happen? Possibly, but well designed external voltage regulators have protections built in..

Balmar regulators have a high voltage alarm circuit and high voltage limits that can be set. We've never seen or known of a Balmar regulator to fail with run-away voltage. We have seen chargers fail in this manner, and one old Heart Interface / Xantrex that was miswired, but not an external regulator such as a Balmar.

What regulator was this?

Parsons · Mar 7, 2019

I would guess that any modern computerized battery monitor would detect and alarm for high-voltage. The Balmar Smartgauge does, for example - http://www.balmar.net/products/smartgauge-battery-monitor/ I know that when my AC-based smart battery charger is conditioning the battery (over 15 V for a short period) it sets off the Smartgauge alarm.

Maine Sail · Mar 7, 2019

kbata22 said:
It was a Hamilton Ferris Powermax alternator and a Powermax Basic regulator.

That regulator is nothing more than an old fashioned "Ford" external single stage regulator. It does not do float and simply holds voltage at what ever it is preset to. It is really more of an inexpensive "emergency get you home" regulator than one designed for deep cycle marine use.

If you motor for a while eventually the batteries will get full but the single voltage set point regulator just keeps on pumping away at absorption voltage. These old fashioned Ford style regs are available in many different voltage set points, and if it is set too high it can dry out or damage the AGM's when or if you motor long enough.

I would not advise replacing it with the same. A Balmar ARS-5 or MC-614 are true performance regulators that can compliment the PowerMax alternator much better.

You can read about how to properly set up a Balmar regulator below:

Programming a Balmar External Voltage Regulator

DayDreamer41 · Mar 7, 2019

Would not a high field voltage for an extended time with little or no load or worse a shorted load cause harm to the alternator as well? Over temperature resulting in insulation breakdown and eventually short the winding in the alternator.
If you are still leery of charging at the wrong (high)voltage you could install a settable voltage sensing relay
http://www.intervolt.com/product/voltage-sensing-relays/#horizontalTab3
but as @Maine Sail indicated a good voltage regulator will not fail with the field voltage high.

Maine Sail · Mar 7, 2019

DayDreamer41 said:
Would not a high field voltage for an extended time with little or no load or worse a shorted load cause harm to the alternator as well? Over temperature resulting in insulation breakdown and eventually short the winding in the alternator.
If you are still leery of charging at the wrong (high)voltage you could install a settable voltage sensing relay
http://www.intervolt.com/product/voltage-sensing-relays/#horizontalTab3
but as @Maine Sail indicated a good voltage regulator will not fail with the field voltage high.

That would not be a good way way to protect the battery as it would pretty much guarantee the alternator diodes will be blown when the relay open circuits the alt at full field due to the over voltage cut off. We are seeing this exact issue with improperly installed drop-in LiFePO4 batteries due to the internal BMS opening circuiting the battery if voltage or temp goes to high.

Now instead of needing just a regulator you'll also need to rebuild the alternator too..

DayDreamer41 · Mar 7, 2019

@Maine Sail I was not suggesting that it be connected between the battery(s) and the alternator,but rather there is a voltage sensing input and there is an output for an settable alarm. I know better than to isolate a loaded alternator output.

Yes, that makes more sense. Course there are configurable built in voltage alarms on Balmar regulators too.