Battery Chargers, Safety, and a FlyBack Burnup

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Robert Mann

This weekend I got to the boat and found the 30 amp breaker was tripped.  Not thinking too much about it, figured it could have been a surge at the dock or a recovered outage I went about the normal chores.  I loaded the fridge and turned it on, don't leave it on any more while we are gone.  Over the weekend I noticed  the charger was hard over at 30 + amps for a seemingly too long time.  Also the batteries were hot and gassing.  These are 4Ds new last October.  Over an 8 hour period I noticed at times the charger would go into the 10 amp mode and then a float charge, but sooner or later back to 30+ amps.  Still only with the reefer on.  I'm thinking the tripped breaker and this over charging are related.

Batteries are not losing water and seem to be holding the charge well (I ran the reefer on batteries only without the charger switched on) but I'm thinking the charger has an intermittant fault.

Does anyone know how to test the Charles charger to see if the regulator is working?  Or has anyone observed the charge condition when the reefer is running?  Any experience with the Charles charger failing in this fashion.

Stu Jackson


What I would do is spend the time to measure the condition of the system.  Start with disconnecting the charger and ALL loads from the boat and let it sit overnight.  12 hours good, 24 hours even better.

Come back the next day, with the batteries having settled overnight, and record the voltage and the hydrometer readings for each cell.  This will tell you what the condition, and more importantly the REAL state of charge, of the batteries are.

Plug in the charger, and keep track of time AND voltage.  If your charger is a true three stage charger, you should see the voltage rising from most likely the 12.8 or so up to 14.2 or 14.4 volts bulk phase charging for about a half an hour (depending on the condition and state of charge of the battery bank - use your house bank).  The voltage will depend on what kind of batteries you have (wet or gel cell) and what the setting on your charger is (if you have a setting, some of the older Charles chargers didn't have variable settings - see - read it all and the referenced links).

After that time, the charger should drop down to the absorption phase with the voltage remaining constant and the amperage tapering off.

The following describes the charging steps from the Ample Power Primer.

Only by measuring what's going on, at your boat with your instruments, will you know if the charger is malfunctioning.  Understanding the following should give you an idea of what to look for.

You can download the complete Ample Power Primer, a VERY good explanation at (click on Technical Documents)

As far as the breaker tripping, there was a recent thread about wiring and connections, which you should also check, see:  Some of the recommendations may be applicable to your situation with the breaker.


The Bulk Charge Step
When a charge source is first applied to a well discharged battery,
charge current begins to flow, typically at the maximum rate of
the charge source. If a true 40 Amp charger is connected to an 8D
battery which is completely discharged, about 40 Amps of charge
current would flow for some period of time. Because most of the
charge is delivered at the maximum charger rate, the first step of
the charge cycle is called the bulk charge step. NOTE: During the
bulk step, battery voltage will steadily rise.

The Start of the Absorption Step
At the instant battery voltage has risen to the maximum allowable
voltage of the charge source, current through the battery begins
to decline. This simultaneous event of reaching maximum voltage
and the start of current decline marks the beginning of the
absorption step.
For instance, if the 40 Amp charger is set to 14.4 Volts, then when
battery voltage has risen to 14.4 Volts, the charger will now hold
the voltage constant. Current through the battery will begin to
decline. NOTE: The charger, (or alternator), is not limiting the
current at this point. The battery is 'absorbing' all it can at the
voltage setpoint.

The End of the Absorption Step
The absorption step should continue until current through the battery
declines to about 2% of battery capacity in Amp–hours as
mentioned above. Without knowing what the current is through
the battery, you can't know when it's full. Just because that fancy
charger, (or inverter/charger), has kicked out to float is no sign
that the battery is full . . . there is no charger on the market that
measures battery current!
It's a given, then, that you need to measure battery current to know
when the battery is full. With a battery current meter, you can discover
some very interesting details about the charge process. For
instance, you can discover that once the charger voltage limit is
reached, battery current begins to decline. If the current decline is
rapid, either the batteries are nearly full, or they are NO GOOD!
If the current decline is slow, then either the charge source has
more output than the batteries can reasonably absorb, or the batteries
are NO GOOD! Here's where Amp–hour instrumentation
is particularly valuable.
Given enough time at the absorption voltage, charge current will
decline to a steady–state value, that is, a low current that either
stays constant, or declines very little. At the point where charge
current has gone as low as it is going to, then the batteries are truly
full. While 2% of Ah rating is close, good batteries will reach a
steady state current at less than 1% of Ah rating.

The Float Step
Once a battery is full, a lower voltage should be applied that will
maintain the full charge. Depending on the type of battery, (liquid,
gel), and the age of the battery, 13.4 – 13.8 Volts is appropriate
as a float voltage.
Stu Jackson, C34 IA Secretary, #224 1986, "Aquavite"  Cowichan Bay, BC  Maple Bay Marina  SR/FK, M25, Rocna 10 (22#) (NZ model)

"There is no problem so great that it can't be solved."

Robert Mann

Thanks Stu, makes sense, thanks for the links and details.  I have left the boat with the shore power switched off.  The only possible load could be a bilge pump, but the boat is a dry one so no issue.  I will get to the problem in a couple of weekends and check the Charles out,  I do believe in 2002 boats they are true 3 stage chargers, but we can prove that out.

Robert Mann

The final part of my battery charger story.
Chased all circuits, checked all connections, watched the battery terminal voltages as they charged and finally arrived at the conclusion that the regulator in the Charles 30A charger had developed a fault.  Replaced the unit with Truecharge 40+.  The notes in the project section of this website are spot on. For a MkII one has to notch the 2X2 that supports the trash can shelf and it fits as near perfect as possible.  The trash can shelf requires a 0.5" spacer but thats only plywood.

All connections made without lengthening wires.  Turned it on an all works just fine, batteries bulk charge to approx 14v and then float out at approx 13v, (haven't checked t he terminal voltages for exact numbers but watched the panel gauge.  Just from initial observation all charging activities take place before the gassing point of the batteries as one would hope.


I had a Charles 30 with a 5 year warranty kept sending it back for free repairs...... :cry4` :cry4` :cry4`
:sleepy: :sleepy: :sleepy:Then finnaly I woke up one day and bought a Truecharge 20 haven't had any problems since :clap :clap :clap

John Langford

Propitious exchange in view of the fact that my ProMariner Flyback 20 began to deliver acrid plastic smoke as we sat around in the saloon on Saturday night. Thank the deity that we didn't go to the movies and leave the charger on or it would have been a much sadder story. The 1999 PM charger had worked fine until Saturday but catching fire as a closing act is not amusing.

I have just purchased a Xantrex Truecharge 20 for the very reasonable price of (C)$289 and look forward to installing it tomorrow.

If you still have a PM Flyback 20 you should give serious thought to turning it off before leaving the boat.
Ranger Tug, 29S

Stu Jackson

Thank you, John, for that input.  We have been discussing chargers for about the last three centuries and have been responding to FlyBack issues for even longer.  John Nixon recently noted in reply #5 on this thread:

I'll try it again:

If you have a Flyback Pro Mariner battery charger, GET RID OF IT, for your own sake.

And, once again, don't say we didn't WARN you.

For those of you who have been reading this message board for many years, there is simply NO excuse for keeping a piece of equipment on your boat that could cause a FIRE.

Rant over...but, please, understand, many of these issues we have been noting are for your safety.  We, along with other Catalina Associations, were the ONLY place to obtain information about the dangers of the late-1980's wiring harness issues (see:, and the C36 Association was in the forefront of warnings about the freshwater pumps on M35 engines.

We do care, but we can't make you do anything.
Stu Jackson, C34 IA Secretary, #224 1986, "Aquavite"  Cowichan Bay, BC  Maple Bay Marina  SR/FK, M25, Rocna 10 (22#) (NZ model)

"There is no problem so great that it can't be solved."


Well, I intended to post a response on this subject a few nights ago, but it was too late for me to make complete sentences.... Try again tonight.

Back to Robert's original posting on this subject, I must point out 2 very important elements: (1) he returned to the boat and found the CB to the battery charger blown; (2) after reactivating the CB and getting the charger working again, he discovered some time later that relatively new batteries were hot and gassing with the charger spending time with it's ammeter "pegged out" at maximum output. Let me pontificate a little on those 2 points.

With regard to point (1), a properly ( mostly.... ) designed battery charger that is working correctly will generally not overload an appropriately rated circuit breaker or fuse. This is because the maximum output current and/or power is electronically limited by one of several means, and the input power consumption is mostly related to the maximum output power. The two possible exceptions to this, depending on the design of the charger, are generally input voltage significantly too high or too low. While this is possible, it is rare in current chargers. The more probable cause for overloading the input AC circuit breaker is a failed charger that has lost its maximum power output limit capability. This generally means that the output stage of the charger has shorted or otherwise failed in such a way that the output voltage of the charger becomes much higher than normal, resulting in a very significant increase in output power which is then reflected back to the input circuit as a much larger than normal input current. The input circuit breaker is there primarily to prevent serious damage from occurring due to a failure in the battery charger. Word To The Wise #1: If the battery charger circuit breaker has blown, be very suspicious about the condition of the charger.

With regard to item (2), properly charged batteries may get warm to the touch after hard charging, but should never get hot. In the case of two 4D batteries on a 30 amp charger, the batteries should never even become noticeably warm during the normal charging process. The exceptions here are: battery is extremely low on water ( flooded batteries only ); battery has a shorted cell; batteries are being exposed to significant over-charging, and generally at excessive voltage ( i.e. - charger has failed in the worst possible way ). By the way, a failed charger producing excessive output voltage can produce not only low water, but also shorted cells in typical flooded cell batteries. Not only that, if allowed to continue for an extended period of time, significant over-charging can also produce an explosion in flooded cell batteries. Word To The Wise #2: If the batteries are hot from what should be normal charging, you have a problem that will only get worse the longer you allow it to continue. A failed charger is the usual culprit.

If you have or suspect a failed charger, a good voltmeter ( preferably a digital one ) is all you need to troubleshoot the charger. Any sustained voltage output from the charger in the normal charging mode in excess of about 14.8 volts means you probably have a problem. Any sustained output voltage in excess of about 15.5 volts means you do have a problem. Don't try to use the typical analog voltmeter found with the engine gauges as a point of reference: they are only slightly better than an "idiot light" as they are notoriously inaccurate.

If you have a hot battery that is gassing, but charger voltages seem reasonable, you probably have a battery problem. Carefully pop the filler caps ( flooded cells only ) and see if all the cells are gassing about equally: a shorted cell won't be gassing. If you can no longer see liquid in the cells, you have a serious loss of water problem, and the battery is likely seriously damaged. Any battery plate material that has been dry for more than about 24 hours is generally permanently "dead".

In summary, pay careful attention to your charger and your batteries. Batteries can be deadly in the correct circumstances, and particularly so in the case of typical flooded cell batteries. They deserve your respect and proper care, which includes protection from serious over-charging. More importantly from a practical standpoint, if you are having battery troubles, you almost are certainly not having fun out on your boat!

To follow-up on what Stu said, there are a few very good chargers, a few more acceptable chargers, and a lot of very BAD chargers out there. The Flyback ProMariner is in the very BAD group. Please get them off of your boat.

John Nixon
Otra Vez
1988 Hull # 728


Understanding there is a lot of info on chargers, and knowing I need to replace my old style transformer type Charles Charger (probably original from 1989), I am trying to draw up a current wiring diagram before diving into buying a new charger, there are a few questions I have. 

As of now, it appears the 110v comes in from the shore power, to the panel, then out to the outlets.  The charger is placed in the port side lazerete, so the 110v to the outlet in the head runs inside the lazerete to the receptacle, then to the charger, and then to the batteries.  (seems odd)  Also, from the charger three wires are run  (green, white, black) just like the 110v wiring to the battery compartment.  The green goes to + on battery 1, white to + on battery 2, and black goes to - on battery 1.

I always thought that the sequence went from the shore power directly to the charger then to the panel, and from the charger you ran wire to the batteries.

Does this seems correct?  I know there are a few wiring diagrams floating around out there, but all see to be for upgrades, and the original manual does not diagram the charger, hence I'm trying to draw up my own, but does anyone have a "standard" wiring diagram or any advice as to what might be going on, please let me know.
2001 C34 #1581
Sandusky, OH

Ken Juul

All though not shown in the Mk1 manual, I have 4 AC switch/breakers, 5 if you include the AC master.  Water heater, Outlets, Battery Charger, and Accessory (now A/C).  If you don't have a dedicated switch to turn the battery charger off you should add one.

Shore power comes in through the galvanic isolater to the panel, then through the breakers to their destinations.  When I installed my Trucharge I placed it under the Nav Table.  Much shorter wire runs and much easier to get to when necessary.  It is common with multi battery bank capable chargers to run a "+" wire to each bank positive and one "-" to the neg bus.  The "+" wires should be fused to protect the batteries from excessive volts/current should the charger go nuts.

Lots of good posts/projects to help you.  Take a look at the knowledge base.
Ken & Vicki Juul
Luna Loca #1090
Chesapeake Bay
Past Commodore C34IA

Ken Juul

I'll hold up my hand as one of the idiots that ignored for a couple years the many posts on doing the wiring harness upgrade.  Mine seemed to be working fine so what is the big deal?

Then I think Ron mentioned in one of his replies that one of the biggest reasons to do the upgrade was to get rid of a very probable FIRE hazard.  Now that had my attention and it was done the next weekend. 

Maybe it was said earlier and I just missed it, maybe it was implied if you read between the lines.  I think we should be more explicit when we discover things that could possibly destroy the boat.  Put it in a red subject line or say Danger or something so any other idiots like me don't miss it.

Additionally for the new users/visitors that are searching for information, critical safety info should stand out.
Ken & Vicki Juul
Luna Loca #1090
Chesapeake Bay
Past Commodore C34IA


In the FYI category, the Truecharge+ series of chargers already have internal fusing on their outputs, so external fuses are not required or recommended. You will normally never blow the internal fuses. However, if you ever are stricken with a momentary case of dumb ass and connect the charger output wires to the battery with the polarity reversed ( not that anyone would ever do that......  :?), the fuses will dutifully blow and leave you only embarrassed rather than with a broken charger.

There are many reasons to like a Truecharge+.

John Nixon
Otra Vez
1988 Hull # 728

Stu Jackson

Ken's right about mentioning and highlighting safety issues.  The following 1997 article is noted, with the point being that back in 1997 much of this website didn't exist and they were printing the Tech Notes information (and still do) in black & white.

The two major SAFETY issues I think of off the top of my hat are the wiring harness and any battery charger that is NOT a Truecharge or combined inverter/charger from Freedom (Heart, West Marine, Xantrex, etc.).

They are problems waiting to happen.  I have been waging an ongoing information campaign about (bad) chargers on this message board for years.  Ron Hill has written just about every wiring harness story ever written.

It is NOT like they haven't been noted many, many, many times.

Of the many wiring harness references in the Knowledgebase this one is noted:


On a repeated basis, both here and in my Secretary's Reports in Mainsheet, I have been noting that owners of older boats NEED to read the material.  And then ACT on it.

I also believe at least an understanding of, and better yet an ability to repair, boat systems is essential to safety.  I didn't know any of this stuff when we bought our boat, but I read the stuff, and I bought the tools, started working on things, skinned many knuckles and feel that I have a responsibility to me, my family and my guests to get them out and back safely.  I know we all do, and some have differening abilities and interests.  But the information availble to us on this website should make it no excuse for anyone to NOT repair those things that are obvious and begin to learn about the others.  In the worst case, some $$ can be saved on yard bills by at least knowing more about the complicated machinery that our hulls surround.

From the May 1997 Tech Notes (by Ron Hill):

Engine Harness Upgrade Do It NOW!
Our November '96 Mainsheet article on electrical systems really stirred up some
interest. Hank, Duane, and I have all received a number of requests for our electrical schematics. But, I still am hearing from people who have not made the engine harness upgrade. So much has been written and talked about that modification, I surely hope that nobody really wants all of the power from the alternator going direct to the key switch in the rear of the boat, then coming back to the battery selector switch, and finally (the few amps left) to the
A few years ago Bill Beck, "Prosit", hull #1186, had just anchored and took
their dog ashore in the dinghy. His wife, Dot, was on the boat by herself when all of a sudden the engine started itself. She tried to shut the engine off but it kept restarting. Dot dove overboard to get off that "crazy" boat. One of the harness connectors had shorted out keeping the starter engaged.
Fortunately the starter burned out before it started a fire. Bill had NOT modified any of his C-34 electrical components and had NOT upgraded the harness.
In the spring of 1991, I installed my high dual output alternator (each output
goes to a battery bank bypassing the battery selector switch). I had the engine
harness upgrade but had not installed it. I did, however, take the harness connector at the engine apart, inspected the terminals, and disconnected the old alternator lead to that connector. Everything looked good so I rewrapped and wire tied the connector. I thought the upgrade installation could wait as  only low amperage would be passing through the connector. The next spring I added Bob Bierly's (C'Mon Wind, hull 913) VHF radio modification in the cockpit (Mainsheet article May 1995). Had to take out the engine instrument panel anyway so decided to do the half of the engine harness upgrade at that end.  Maybe a month later I got around to the other half of the modification at the engine. To my surprise, when I took the connector apart, the side with the male pins crumbled in my hand.
If you haven't made the engine harness upgrade, you may want to reconsider.
Stu Jackson, C34 IA Secretary, #224 1986, "Aquavite"  Cowichan Bay, BC  Maple Bay Marina  SR/FK, M25, Rocna 10 (22#) (NZ model)

"There is no problem so great that it can't be solved."

Stu Jackson


I note that Sundance has a Mark I by the #844 hull #, so the galvanic isolator is most likely nonexistent.  Also the incoming Marinco fitting is on the port side into the port locker, not at the stern.  The split transom boats were different.

As of now, it appears the 110v comes in from the shore power, to the panel, then out to the outlets.  The charger is placed in the port side lazarette, so the 110v to the outlet in the head runs inside the lazarette to the receptacle, then to the charger, and then to the batteries.  (seems odd)  Also, from the charger three wires are run  (green, white, black) just like the 110v wiring to the battery compartment.  The green goes to + on battery 1, white to + on battery 2, and black goes to - on battery 1.

Each boat may have been wired differently.  Our boat does NOT have an A.C. voltage switch on the panel for the charger.  (Note: We replaced the old charger with a combination inverter/charger, but I won't discuss that here.)  So, without the switch on the panel, every time the boat was plugged in the charger was energized.  It appears from your description that you may not have a charger switch on your panel either, and that the wiring to the charger is fed from the outlet in the head.  Your description is somewhat inconsistent because you also said: "the shore power, to the panel, then out to the outlets..."  Do you have a charger switch on your A.C. panel?  Or is the charger wired either directly to the shorepower or to the head outlet?  Please let us know what you do have, because further discussion will depend on this.

This website has the manuals at, left side index.  If you haven't, download and print out the wiring diagrams.  The Mark I manuals don't have the charger because I recall that chargers were aftermarket dealer installed equipment "way back then."  So, print out the Mark II diagram which shows the charger and they way Catalina is installaing them now.  Can't hurt.

Your description of the green, white and black wires seems suspiciously WRONG.  Those three colors are the ones for the A.C. INPUT to the charger, not the D.C. output of the charger to the batteries.  I recommend that you check this out carefully again and get back to us.

I always thought that the sequence went from the shore power directly to the charger then to the panel, and from the charger you ran wire to the batteries.  Does this seems correct?  I know there are a few wiring diagrams floating around out there, but all see to be for upgrades, and the original manual does not diagram the charger, hence I'm trying to draw up my own, but does anyone have a "standard" wiring diagram or any advice as to what might be going on, please let me know.

Doesn't sound right.  The sequence should be:  incoming shorepower to panel, and switch (main breaker and individual charger switch) then to charger (A.C. - alternating current); the D.C. charger output to the batteries (some people have wired this via the back of the 1-2-B switch - done sometimes - or better yet directly to the batteries).  The charger is simply a transformer:  it takes A.C. current and transforms it down to 12V D.C. current to charge the batteries.

I recommend that you check out a good charger website and perhaps download an installation manual.  Try this for starters:

This is the VERY good charger that John mentioned before.

Do a little bit more looking around, maybe even draw your own diagram of what you have 'till it starts to make sense to you, then get back to us. 

I've found it's sometimes easier to draw a wring diagram over a floor plan of the boat, showing where the wires run physically, rather than a more abstract "wiring" diagram.  Your choice.

The West Marine Advisors, both online and in their catalogs are also very helpful, as are many websites you can Google.

Look forward to hearing from you soon.
Stu Jackson, C34 IA Secretary, #224 1986, "Aquavite"  Cowichan Bay, BC  Maple Bay Marina  SR/FK, M25, Rocna 10 (22#) (NZ model)

"There is no problem so great that it can't be solved."


You are correct, I do not have a switch for the charger at the panel.  I may have misspoke, the current sequence of AC power from the beginning is shore power to panel, from panel to outlets (specifically the outlet in the head), from the outlet in the head to charger (transformer), from charger to the battery (current suspicious three wire set up).  The output from the charger is the same three wire (white, green,black) as is going in.

If I turn the outlets off, the charger is turned off, makes sense in theory, obviously the charger is aftermarket and connected to the AC power via the head outlet (acting as a junction box). 

I'm trying to draw up a wiring diagram, probably trying to be too specific (the engineer in me), but as I'm sure you know it is a process, everytime you think you got it, some random wire throws you off course.  I'll get it.

I was very suspicious of the three wires to the batteries.  I wish I had the original manual for the charger.  I believe you have confirmed that infact most people have a separate breaker for there charger and the current set up I have is suspect.  I will report back if I find something diffrent this weekend.

I think I got it:

Here is my thought of what the PO was guess is that the white and green are both + wires, the thought being if he wired directly to the batteries (not through the 1-2-both) he wanted to charge both batteries, so simply connecting to one battery would not charge both, so by connecting the charger via two + wires (should have been two red wires) and then a black to the -terminal (- terminals are connected between batteries) he could charge both batteries directly from the charger.  In short he used the wire he had available.

Sorry for the jumbled respose, I was brainstorming as I was responding.
2001 C34 #1581
Sandusky, OH