Minn Kota On-Board Charger Problem

[daniel123]

I have an older (five years or so) Minn Kota 220 on-board, two-bank 20 amp (10 amp per circuit) battery charger hooked to my Optima starting battery and my Interstate deep-cycle aboard my Osprey 200, powered with a 1999 Johnson 115. It worked fine until I unplugged it and took the boat to Lake Erie last weekend and ran the outboard with the battery selector switch turned to "ALL" to help keep both batteries charged via the engine's alternator. I didn't plug the charger in all weekend as our docks didn't offer power. When I returned home and plugged it back in using the usual extension cord from my garage outlet out to the trailered boat, I checked and noted both banks' "Check-Connection" lights we're lit on the charger under the console, and found that both in-line fuse holders to both batteries had melted around the glass fuses. Any ideas about what went wrong? The charger claims to offer "Fully Automatic Short Circuit/Reverse Polarity/Ignition protection and is for use with 12 Volt/6 Cell batteries that are flooded/Wet Cell, Maintenance-Free or Standard Electrolyte Only" if that helps.

I don't want to just re-wire some fuse holders (I'd use blade style rather than MK's stock inline-for-glass fuses) in the lines and have it happen again.  Any advice is welcome.

[GoneFission]

Some chargers isolate the batteries in order to charge.  They will treat 2 batteries linked together as a short.  Check the output on the charger for each bank - if the output is OK, you should probably just replace the fuses and chalk it up as a lesson learned.

[daniel123]

Thanks for the input, John. So, based on the charger's output being ok, it might have happened if I turned the battery selector to ALL while the charger was still plugged into the wall and charging both batteries? I'm not actually sure when I switched to ALL, but it might have been before I unplugged the charger, but again, I'm not sure. I'm pretty sure I waited until we were about to launch and the battery charger was unplugged (from the electrical supply, not from the batteries, which it stays connected to). Otherwise, you think that having the charger hooked up to both batteries and then switching to ALL and allowing the outboard to charge them might have triggered a short or backed-up through the batteries and charger and shorted/overcharged them? How do I get around that in the future?

[seabob4]

Sorry JJ, but this configuration is very common out on the water, even in an ACR or VSR install where the batts are combined via relays rather than the batt switch.  In other words, nothing at all wrong with the install, nor the way Daniel was running the boat.

Daniel, unfortunately we cannot determine whether the over-amperage or over-voltage situation occurred as a result of the batts or the charger, since you stated you plugged the charger back in, on to come out later and find the fuses blown/melted.  If you had observed the blown fuses BEFORE you plugged the charger back in, then we would safely say the batts were at fault.

Seeing as you said the fuse holders had "melted" around the glass fuses tells me an amperage issue.  Over voltage will cause heat, but over amperage will cause a LOT of heat.

My best bet is it's time for a new charger.  I would recommend either Guest or ProMariner, as there are a lot more of them out there then Minnkota for a reason...

[daniel123]

Seabob,

When I got back, I plugged the charger in and checked the charging right away and discovered the check connection light and the melted fuse holders within a minute or so of plugging the charger into the wall, so if the short/surge happened then they would still have been hot, or at least warm. I think it happened sometime over the weekend, when the charger was not connected to wall current. You said if that's the case you to think it's the batteries that caused the meltdown, but it's weird that the fuses to both batteries overheated and blew, and not just one. Could the outboard's alternator have back-charged?

I have another new 2 bank MK charger (albeit 5 amps per bank, not 10) I can install -- which actually has fuses in both positive and negative wires (the 20 amp one that I was using had only fuses in the positive wires) -- but I hate to install it and have the same thing happen, plus I kind of want to know what went wrong just for peace of mind.  

Thanks for the input!

Dan

[daniel123]

I am still hesitant to simply re-install my charger on my boat until I have an idea what caused both fuses to melt. Could it be turning the battery selector switch to ALL while the engine was running? I'm not sure I did that, but would that cause the failure?

[dburr]

Dan the thing that sucks is that the bottom line is we can only guess, Bob said essentially said replace the charger..  

So, my present barley fogged state of mind (visiting the inlaws..) I say change the charger and let'er rip..  Unless I am really fogged, when you go from either 1 or 2 to both on the main switch, you do not unmake either connection until it is deselected so there should be no voltage surge...  So, switching from 1 to all 1 stays connected from 1 to both... Bob square me away if I am wrong!!!!! Belgian ale RULES!!!!

So, the rest of the system appears ok to you? If so, if you are worried, make sure the fuses are clean, if they melted then they were too big for the holder (made too much heat) and make sure they are the correct size, tell Bob what the wire size is and he can tell you capacities faster then you can google it..

Other then that I got nuthin....  

[seabob4]

Sorry for the late reply to your question Dan.  Safe to assume the "melt down" occured when the charger was simply along for the ride, we have to look at the charging system of the motor as the culprit.  However, that involves an "over voltage" situation, not an over amperage one.  A failing alternator will not put out more charging amps than a good one.  But a failed voltage regulator will cause the output amps to be at a much higher voltage, sometimes upwards of around 19VDC, which over a small period of time will cook your batts, as well as a few other items.  What was your voltmeter reading while underway, both at idle and cruise?  

And Dave is correct, battery switches (although I don't believe the switch had anything to do with this situation) are what we call a "make before break" configuration.  Contact is made by battery 2 before it is lost from battery 1.  The reason for this is that the alternator output needs to have something to output to.  If not, the inherrant charge will have nowhere to go and overwhelm the diode in the alternator, hence frying it...

[wingtime]

I bet you have some sort of short in the charger itself.  Having the battery selector on both would only parallel the two ten amp chargers into a single twenty amp charger. Maybe a rectifier or diode failed.

[daniel123]

Thanks for all the excellent input, guys. I'm going to replace the fuses and re-install the original charger and see if it occurs again; if so, I'll put in the new charger and see what happens. If the fuses melt/blow again, I'll figure it's probably a problem with the engine over-charging and start troubleshooting that. 'Sound like a reasonable plan?

The certified electrician/angler friend who helps me work on the boat (who I respect and is very particular about his own set-up) is telling me to remove the selector switch, and have one house battery for starting and accessories, and a separate deep cycle (or two) to power the 12-volt-bowmount and maybe the baitwell, and not allow them to be inter-connected through a selector switch. He said to use the two-bank charger, one circuit on each, and just make sure each battery is charged before every trip. (He actually recommends two deep cycles in tandem to run the 12 volt trolling motor for a longer amount of time).  He claims the selector switch simply increases the potential for more problems, and that by using one I am preparing myself up for failure by counting on it as a back-up option to allow me to combine both batteries if I ever need to.

I like the selector switch because it allows me to charge (starting, deep cycle or both) batteries when the engine is underway (right?) and it gives me the ability to combine the juice from both if I ever need it to start. I welcome members' thoughts.

Dan

[dburr]

Keep the selector switch..

There are a few different ways to keep everything charged..  SB, the floor is yours..  

[wingtime]

Keep the selector it is not the problem.  I have a buddy of mine that is a licensed electrician.  He simply does not understand DC wiring.  It is a total different animal to a guy used to wiring AC.

[seabob4]

Agree entirely Dave.  A properly functioning electrical system poses no threat to melt-downs or loss of power...assuming all the pieces of the system are properly functioning as well.  Removing a battery switch out of the system is simply masking a problem within the system that needs to be addressed, so I completely disagree with his thinking...

Batteries are combined via battery switches daily by thousands upon thousands of boaters throughout the world...EVERY DAY!  In fact, the method I tell boaters on how to use their batteries is to start the engine on batt 1, then turn the switch to ALL (or BOTH) when underway so that both batteries are getting charged by the alternator.  In fact, most boaters turn the switch to ALL even before starting the engine.

Me thinks your friend needs to learn a little bit more about the 12VDC side of things.  And I will wire a house for you, 240/120VAC.  Bigger boats have both, you know...

[daniel123]

Seabob,

That's been my experience as well, when using switches, and why I want to keep one aboard. How do I check to see if the engine is charging each battery, and how much juice it's directing toward same?

Dan

[seabob4]

Pretty simple Dan, a multimeter will do the trick.  Check each battery for rest voltage (should be between 12.25 and 12.5 volts).  Fire up the motor, now the voltages should check between 12.75 and around 13.2.  If you have a buddy driving, check them again at cruise (say around 3500-4000 RPM).  You should see around 14V on each.

Without a clamp on ampmeter, you really don't know how many amps each is receiving...