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Alternator Voltage Regulation For LiFePO4

A good voltage regulator is critical for an LFP bank. It is my belief that no better regulator currently exists for LFP than the Balmar MC-614. This regulator allows every conceivable parameter to be adjusted from; voltage, to alt temp compensation, bulk, absorption and float duration, thresholds for transitions from bulk to absorption or absorption to float, the ability limit the field current and do "current limiting" of your alternator etc. etc. on and on. Of critical importance in LFP it also uses a dedicated voltage sense wire that does nothing but sense voltage, this wire carries no current on it, so you get an accurate reflection of battery terminal voltage, provided you wire it correctly.


#1 User Defined Charging Parameters: Adjustable bulk, absorption and float voltages allow you to tailor the regulator to suit LFP banks. Float can be set low enough so that it essentially turns the regulator off when the bank is "full".

NOTE: In order to get the voltage settings low enough for LFP banks one must work backwards in the custom programing menu by starting with float first, then absorption then bulk. If you want BULK at 13.9V you need to lower/adjust ABSORPTION to 13.8V first. This is because BULK can't be lower than ABSORB. There needs to be a minimum of 0.1V between "stages". I use: BULK = 13.9V, ABSORB = 13.8V FLOAT/OFF = 13.2V

#2 Dedicated Voltage Sense Lead: This feature is not to be underestimated on an LFP bank. ACCURATE voltage sensing is of critical importance. The MC-614 v-sense wire does nothing but sense voltage. On the ARS-5, the next step down, this wire both power the regulator and senses voltage. This can create inaccurate voltage sensing due to the additional current carried on the v-sense wire to power the regulator.

NOTE: In order for the v-sense "circuit" to work correctly, and accurately, you must wire the regulator negative lead directly to the negative post of the battery bank which you are measuring.

#3 Current Limiting: Remember when I said there is no alternator on the planet that can run at full bore for 3+ hours into an LFP load in boats engine bay..? Well this is where you fix this and help save and extend the life of your alternator. Balmar calls this BELT MANAGER it was formerly called AMP MANAGER, which I still feel is a better term, but it works for both belts and saving the life of your alternator. Current limiting allows you to essentially derate the output of your alternator by limiting the maximum field potential to the alternator. The field wire from the regulator is what drives the alternator. Simple stuff. By limiting the capability of the field wire you in turn limit how much current the alternator can drive. This is a simple adjustment in the settings menu and should be made when the alternator has been run up to temp.

Every alternator will be slightly different but usually Belt Manager level 3 or 4 is a good place to start. I generally suggest buying an alternator that is larger than where you want the expected hot rated output to be and then dialing it back in Belt Manager..

As an example I run a 160A Mark Grasser DC Solutions alternator on our boat and she is current limited to 120A. She will drive at 120A all day long and never break 220F. This is exactly what I want to see. I do this by limiting its max potential using Belt Manager. This keeps the alternator from melting itself down and prolongs its useful life.. It also gives you a known value for charge current that won't vary due to temp limiting or heat...

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Chris 30-Jan-2017 02:51
This is a great article and I am inspired to try a 100 or 160 amp hour house battery bank. I already have a balmar ARS-5 on the boat so despite the benefits of the dedicated voltage sensing of the 614, would like to at least try the ARS-5 first to see it does not over change the LifePo4 batteries when set to bulk of 14.1 (the lowest it will go) and float to 13.2. I also have a small 80 AH AGM starter battery on a separate battery bank. You mentioned in your article that you also had a back up lead acid battery. My Balmar charges both banks when the engine runs and they automatically separate when the charge current is not present ( via a Blue Seas Si-ACR voltage sensing relay). My question is, can i combine a lead acid starting battery into a engine charging system without running the risk of over charging? The start battery will likely take very little current as it will always be close to full. Do i need a separate regulator or alternator for the start battery? How do you mange to charge your second battery in your boat? Thanks in advance for any thoughts on this topic.
Toby 05-Sep-2015 08:10
Thanks for all this info it sounds like you sure know your stuff. I "dropped in " these same 400ah bank into our cruising yacht we live on permanently 3 years ago and they seem as good as the day I put them in. We run a fridge/freezer and all the rest of the gear and when on passage autopilot ect. We have 420watt of solar and just use a standard PWM regulator set to gel, absorption to 14.1v floating at 13.7 and standard 130amp alternator sometimes we have had to motor for days on end with batteries at 14.4v. I have no BMS and don't see the need when only have 4 in series, have isolated and checked each individual cell many times and all the same.
I think you can make this system very technical and I'm thinking that may come with many problems down the line and may be hard for the average sailor to work out when your in remote places far from getting spare parts and all the electronic gadgetry. We have kept it very simple and monitor voltage constantly and touch wood it has been fine. Just saying;)
Time will tell but I truly think if you don't over charge them and drain the hell out of them they should last for many more years. Thanks again for all your info.
Toby, sv Sj Sunflower