House battery not charging

[mylo]

I have a feeling that the charger on my rig died... The discharged battery was showing 9 volts yesterday, so I plugged it into shore power. It was probably on there for 15 hours, and the battery was still dead. So I just plugged in my small battery tender that I keep my pickup truck on, and the battery was charged in about 3 hours.

The converter part works fine. I can use all 12v devices when on shore power. This is my first RV - so I don't know what is "typical" for battery charging time. So, a few questions... Is there something I can troubleshoot? There are no blown fuses... Is there a sub component of the converter that I can replace (transformer)? And finally, if I have to replace the whole thing... What do I look for in a new one? Thanks.


Mylo

 

[Bob Buchanan]

What is the brand name on the converter? If Magnetek, you are probably better off buying a separate 3-stage charger. In all 5 RV's I have had in the past 15 or so years all but one (a 98' Tioga) had Magneteks. Those chargers were not 3 stage so would boil the batteries - leading to replacement earlier than normal.

On some of my RV's, the charger was on a separate breaker, on others I had to find the proper wire on the bottom side of the converter and just cut it to disable. I then purchased a Statpower (Zantrex) 40amp charger. I mounted it along side of a 1500W inverter on one of the bulkheads up front. I plug the charger into a rig 110 outlet on the same bulkhead - and run run the cables to the battery bank. Actually, I plug the charger into a power strip so I can easily turn it off when boondocking. HERE is a used one on eBay - a bit newer than mine. New would probably run around $350.

You could also upgrade the Magnetek converter that includes a better charging unit than you have now. HERE is an example on Amazon.

 

[Alfa38User]

I would be very surprised that the battery was fully charged in only 3 hours, especially if a battery tender charger (float charger) was used. If you measured it immediately after taking the charger off you would be reading a higher voltage but that surface charge voltage would disappear within an hour or two. A fully charged battery should read in the neighbourhood of 12.3 V several hours after charging has stopped and with no other load on it.

It normally takes up to 24 hours to charge a battery fully unless you have a high output charger such as those used in a commercial battery shop.

 

[Gary RV_Wizard]

It would also be very unusual for the converter to be working but not charging. In a coach of your vintage, it is likely a Magnetek that has separate leads for the charging output, and very low amperage on that side.  Could be a broken wire or bad connection rather than a failed charger.

The old Magnetek takes a very long tme to charge, but so would the trickle charger you mentioned.

 

[dan2]

I replaced my battery charging board last week. I have a Progressive Dynamics: if you have a charge sentinel, make sure the red
light is on when on shore power. Under $50 bucks to my door the next day 

Dan

 

[mylo]

Well, I did more poking around. It is a Magnetek 6345 (45 amp). It's the original that came with the coach, so it is 20 yrs old. I did find some troubleshooting documents, and I intend on verifying the charging circuit, and/or limit resistor (which seems to be typically the issue).

As far as the aux charger that I used, it was a high output, smart charger. I was in a rush, so I couldn't actually wait an hour afterwards to test the output voltage - but I can tell you that it was able to take the house battery from "low" on the RV panel, to "good" in three hours. I even checked it a day later, and it was still "good".

I assume that boondockers can actually charge their house batteries in a reasonable amount of time, by running their generator, no? I don't think it's practical to run it for 24 hours, but maybe 2-3. The "upgrade" that Bob posted below claims to charge a battery to 90% in 3-6 hours. It is a 4 stage (includes an "equalization mode" every so often that prevents stratification, whatever that is). I assume that it is comparable to other replacement converter/chargers. I guess the benefit here is that it is a direct replacement that will fit right into the old enclosure.

They actually sell three different amperages - 35/45/55. I only have a 30amp cord on my coach, so I am a little baffled about what that rating means. Could I safely put in the 55 amp one, expecting even better performance?

Finally, not to derail my own thread, but I did have a question about the transfer switch. I have a three position manual switch in the head (generator-off-shore), that I can't figure out the use for. It must do some auto sensing - because once I shut off my generator with it in the generator position. The lights dimmed, and then switched automatically to battery... So what is the point of the middle position? Complete isolation from 110v sources? I guess I should leave it in the "shore" setting all the time - which will auto sense when I plug in - and just use it to prevent loading the generator until it warms up, properly?
I assume that charging happens in both outer positions - but might not happen in the off position (I did not use this position while trying to charge my battery off of shore power this weekend).

Anyway, thanks for all the suggestions and further help/clarification of my charging problems.



Mylo

 

[Alfa38User]

They actually sell three different amperages - 35/45/55. I only have a 30amp cord on my coach, so I am a little baffled about what that rating means. Could I safely put in the 55 amp one, expecting even better performance?

The 30 amp shore power cord  is at 120V AC amps (=3600 watts) whereas the rating of the chargers are in DC amps at 12V (45amps at 12V =540 watts)...  a big difference.... So the answer as to whether you can or can use a bigger one, is YES. Would it help, perhaps a bit but no big deal!!

Not sure about that manual switch but auto transfer switches versions do have a built-in delay to give the generator time to spool up and reach operating specs before switching the generated power into the RV. They are installed normally so that the 'normal' is to have shore power available on plugging in and generator power only available once the genny is producing up to scratch. The usual 'manual' transfer switch consists of plugging a cord from the generator into the socket normally used by the line cord from shore.

Was this switch perhaps added by a previous owner?? It sounds an awful lot like a marine battery switch (off,  Bat 1, Both, Bat 2) normally used on a boats 12V side. I wonder if a PO tried to automate the cord switching method mentioned above.

 

[Bob Buchanan]

What do you do with the 30amp cord when you unhook from shore power. Do you then plug it into a 30amp plug somewhere on the rig -- near where you store the 30amp cord?

My rig is a '96 and came with a Magnetek - so I have done a lot of mods to the electric. When I unplug from shore I plug the 30amp cord into the outlet that is actually "output" from the genset. So when the genset is running power continues through the 30amp cord to the converter.

The switch you mention may be switching between genset and shore power -- that's why am wondering about your cord when you unhook. If the switch "is" switching between genset and shore - then the middle has neither connect to the converter. So when in that position, the converter simply shifts to DC power w/no AC. That would explain the lights dimming. They are not getting "converted" DC from AC coming in, but rather just from the batteries.

 

[mylo]

What do you do with the 30amp cord when you unhook from shore power. Do you then plug it into a 30amp plug somewhere on the rig -- near where you store the 30amp cord?

I don't do anything with it. I just stow it in its side compartment.

... That would explain the lights dimming. They are not getting "converted" DC from AC coming in, but rather just from the batteries.

What I meant was that when the switch was in the generator position, I shut down the generator. Just as it was slowing, the lights were dimming - and as soon as it stopped - the lights came back on full strength from the battery. I assume the same would happen if I watched them while the switch was in the shore position and somebody unplugged the rig (albeit much quicker ). There is probably just a relay that gets pulled in from some 110v on the input that feeds the charging circuit or something. There is no automatic timer or anything that switches to the genny. The more and more I think about it - it's probably just a manual disconnect that prevents backfeeding the shore from the genny and vice versa. I assume that if I want to charge/convert from either source, I need to select it manually. It's weird that there is an "OFF" position - but that is probably just a safer "break before make" mechanism.

One mystery solved, thanks. Now if I can just verify that the charging circuit is faulty, I can make plans to try to either fix it or replace it.


Mylo