The Mechanics of Battery Equalization

amelliahona <no_reply@...>

Hi All:

My 50 Amp Dolphin Battery charger (original Amel) suddenly died upon re-commissioning the boat after our hurricane repairs.  Having an electronics background I contacted Dolphin for schematics and a parts list which they promptly provided for this 17 year old product, (wow, I was impressed, and when I have a moment I will post those items in the files section).  As usual the failed parts were two capacitors (that seems to be the most common failure mode for all things electric on our boats).  The exact part number was available and I obtained those and installed them and voila, the beast is alive.  The LED indicators also went at the same time, so I found replacements for those cute little rectangular LEDs, replaced them, and checks show everything is working as prior including the multistage charging etc.  Total cost about $16.00 US and a day's labor at my exorbitant shop rate of $0.00 per hour.  If you actually paid someone to render this repair it would probably be cheaper to buy a new charger.

My chargers don't have an equalization mode so I have been using a DC power supply to equalize pairs (4 pairs) at 31 volts at 5 amps.  This is laborious (2 day) process but forces me to carefully watch the process and monitor temps, water levels, specific gravity etc.  I also isolate each pair from the boat during the process to avoid any damage to any boat items. 

As I considered a new charger (just in case I couldn't fix the Dolphin 50 A), I found that I couldn't find any marine 28 volt DC, 50-60 amp output, input 220-230 volt, 50-60 hertz chargers that have an equalization mode.  Blue Sea makes one but it is a max 40 Amp DC output,  Mastervolt and Victron don't have any with an equalization mode (at least that I could discover in their literature).  So I have two questions for the group:

1.  What charger do you have that has an equalization mode?  

2.  When you do the equalization, how do you isolate the house bank batteries from the boat? (I know that turning off the two large red handles in the quarter-berth companionway turns off most of the power to the boat, but I wasn't certain if there are "sneak, hot battery bus" type circuits that are wired (e.g. inverters, solar panel regulators etc).  The chargers do NOT go thru the large red handled shut off switches.  

Your thoughts and experiences would be most welcome. 


Gary S. Silver

s/v Liahona

Amel SM 2000 #335

Puerto Del Rey Marina - Puerto Rico

Thomas Peacock

Hi Gary,
Our boat came with an original owner requested, LaRochelle installed modification which included a Heart 24v DC/220 v AC inverter/charger. We have been very happy with it. It is no longer made, but Xantrex ( I believe same company, different name) does have a new 24v/220v model with equalization capabilities. Some of the tech specs are beyond me, but you could start there if future brain surgery on your charger is not successful.
We did equalize our flooded cell batteries early on, but have been using AGM also with good results, although our 20 year old charger does not have a charge setting for AGM.

Tom Peacock
Aletes SM 240
St Augustine, Florida

Mark & Debbie Mueller

Hi Gary,

We have Mastervolt chargers and they do have have an equalization mode.  By the discussion in the manual you can dicern that the equalization mode is not intended to be used very often.  Below is an excerpt from from the manual: 

"An equalizing charge can be necessary after very deep
discharges and/or inadequate charges. This has to be
carried out according to the specifications of the
manufacturer of the batteries.
During equalizing the batteries are brought into the gas
state and is it possible that the permitted load voltages are
exceeded. Therefore appropriate measures must be
taken, e.g. disconnect all loads from the battery and
ventilate the room. For these reasons use of the equalizing
mode should only be executed by trained technical
The equalizing mode can only be started when the
Chargemaster is in operation and in Float. This means that
the connection compartment of the Chargemaster must be
opened while connected to the mains and the batteries.
Take adequate measures for protection against short
circuits and electrical shocks.
To start the equalize mode: move DIP switch 4 to the ON
position and back to the OFF position."

Mark Mueller
Brass Ring A54

amelliahona <no_reply@...>

Hi Mark, thanks for that, what Model of Mastervolt charger do you have?


Mark & Debbie Mueller

We have a ChargeMaster 24/30-3 & a ChargeMaster 24/100-3.  The 30 amp charger is the newer of the two.  Mastervolt was introducing a 40 amp version that would charge both the 24 & 12 volt batteries (engine starting and house) but it was not yet available when we had to replace the Xantrex that died and toasted our 12 house batteries.

Mark Mueller
Brass Ring A54