Quote Originally Posted by albecool View Post
I wish i had read this post sooner. I switched to Lifepo4 batteries for my Fishpro last year and love them as well. Much better cranking power, light weight and while fishing I can run the bilge pump, and stereo without the annoying low battery warning. What I didn't know about was the voltage regulator, I have been using my OEM with the lithium batteries and I think I fried the Regulator last week. I was getting erratic behavior on my instrument panel and I also have a VHF radio installed on the boat that was giving me Battery High warnings. I checked the charge voltage and is was exceeding 15.3V and was very unstable jumping from 13.5-15.3V, just learned about the Mosfet, and I have ordered one from eBay for $129, it sounds like it should resolve the issue.
What might have occurred (aka the voltage swings) is not foreign to SCR type regs, as they often rely on the connected battery as a “source” of voltage reference. So if the battery goes bad, or the connections are poor, this can indeed happen. So I’d make sure (in addition) that all your connections are sound and that your battery is not defective/damaged.

That said, I’ve add a few more notes below, for the benefit of anyone else considering switching away from lead acid technology.


A quick note on SCR -vs- MOSFET R/Rs…

BLUF: mosfets offers better shunting, less heat, and more precise voltage regulation over its SCR cousin.

Longer version

There are two major types of OEM voltage regulators/rectifiers on the market – ironically made by the same vendor. Both do their job well, but one does it a bit more efficiently, and therefore a “better” choice, especially when using LiFEPO4 technology.

They work fundamentally the same (shunting excess current to cancel voltage excitation within the stator – aka regulate Power output), and they both convert AC to DC. However, there are mainly two functional characteristics (shunting method & voltage regulation), that sets them apart – with the MosFET doing a better job at BOTH :

Characteristic 1 – shunting :

SCR type:
“The” most common type found in vehicles (PWCs, motorcycles, snowmobiles). Cheaper to manufacture as these contain very simple and less components. Silicon Controlled Rectifiers (SCRs) to both current and rectify. The major pitfall with SCR components, is their inability to produce a pure conductive path – aka they are slightly still resistive – and therefore generate heat, lots of heat. Example, when shunting a 500W stator, there can be as much as 50+ watts dissipated, which is why the device has fins. Ever touch a 60W light bulb – hot – yet that’s normal. SCRs also stay in shorted mode until “reset”, meaning they are shunting more than needed. Yet in the end, these regulators are true tried and proven to work well.

FET type:
Looks exactly like an SCR type, but uses more sophisticated circuitry. Field-Effect Transistors (FETs, MosFETs) to conduct the shunting – which is it’s greatest advantage, as mosfets offer a nearly pure conductive path, a mere 5W dissipation – way less heat. Shunting is also “smarter” in-that only the excess sine-wave portion is ever shunted.

Characteristic 2 – voltage reference (regulation) :

SCR type:
Really poor target voltage regulation. In-fact, there are many really old-school SCRs out there that actually require a battery be connected, as these regulators use the battery’s voltage as the voltage reference. So if the battery goes flaky (or the wires), one can see wild regulation voltages. That said, newer SCRs typically have an internal voltage reference, and while better, still not perfect (especially at low RPMs – aka idle). This is why one can see as much as a 1.5 volt swing between idle and on-throttle RPMs. 12.8 – 13.4 is typical. At idle, that 12.8v is not recharging anything! Worse-yet, if you are running LiFEPO4, that 13.4v really isn’t charging much either, due to LiFEPO4’s having a higher operating voltage than lead acid/AGM batteries.

FET type:
The main reason I stated these are better for LiFEPO4 setups, is that mosFET regulators also have vastly more improved (read-in: more stable) internal voltage reference circuitry. A FET will and can typically maintain an higher and more stable (with a fully charged battery attached) 13.8 – 14.1 volts of regulation in any RPM range – including idle!

Contrary to many who claim shunting regulators (SCR or MosFET) “wastes” Power - it’s simply not true. Shunting basically (layman’s terms here), shorts, in a timed sequence, the current from one of the three phases across the other two phases, as to complement the magnetic fields proportionally to the proximity/location of those other two phase windings from the magnetic poles. Basically a temporary “magnetic slips” occurs, as the rotor free-wheels, no drag on the engine in that state. And because 99.9% full-current is flowing, voltage cannot build-up, aka 0 volts = aka no Power is being produce.