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How to figure out what electrical components are present.

DRTDEVL
Explorer
Explorer
OK, I have almost finished prepping the RV I inherited from my grandparents for actual use, and plan to use it extensively this summer.

The specs:

1980 Winnebago Minnie Winnie 20RG
1979 Dodge CB300 Chassis with 10,400 GVWR heavy package.
5.9L 360 c.i., 727 Transmission
Generator Prep package (but no generator)

There is no power inverter, only a power converter and "charge sentry" system to keep the 12v up and running when plugged in. At least, I don't think there is an inverter, as I have never seen one nor any switch or remote panel that would turn on the 110v system when not hooked to shore power.

I plan on mounting a 3000w continuous (6000w peak) inverter with a remote panel in the generator bay, as there is already a large gauge positive battery cable running there as well as an electrical junction box to wire a generator to the 110 system. This seems to be the most logical choice for me... but I don't know if there is an automatic power transfer switch installed from the factory as a part of the generator prep package. Later today, I am going to remove the back seat and check to see what the back side of the converter/breaker/fuse panel looks like, but I am not sure if I would recognize an automatic transfer switch from 38 years ago. If not, I can always try to remember to turn off the inverter prior to plugging into shore power, but I would like to make it "dummy proof" in case someone else is hooking it up in the future.

Anyone know much about these old units?
Resurrecting an inherited 1980 Minnie Winnie 20RG from the dead after sitting since 1998..
23 REPLIES 23

MEXICOWANDERER
Explorer
Explorer
Doubled same electrical wire

Start counting down

Example 2 x 10 AWG

Down three places

Nine

Eight

Seven

DRTDEVL
Explorer
Explorer
DrewE wrote:
DRTDEVL wrote:
4/0 is 0.46"
2 awg is 0.2576"
2x 2awg is 0.5152"

I believe this will pass the same, if not more, power capacity, while saving money. After all, 4/0 cable is about $4/foot and 2 awg is less than $2/foot. I'll need about 10 feet each for the positive and ground, so this is the difference of $20 in cabling for the same capacity.

Unless I am wrong, then someone correct me. I don't want to burn the thing down.


It's not the same, for a couple of reasons. First, you're comparing diameter rather than cross-sectional area, which of course for a round wire is pi r^2. Here is a nice chart where the math is done for you; 2 AWG has a cross-sectional area of 42.4mm^2, and 4/0 has a cross-sectional area of 107 mm^2. Two and a half 2 AWG wires would be just about equivalent.

The second reason they are not equivalent is perhaps of greater importance. If one of the ground wires were to work lose or break or corrode and have a (relatively) high resistance, you may never notice the difference in performance but the one remaining good one would carry most or all of the current and be overloaded. Even under good conditions there is likely to be some current imbalance as the impedances will not be precisely equal, and it doesn't take very much resistance at all to cause a fairly significant difference for a chunk of wire.

Can't the grounds connect to the trailer frame itself? I wouldn't think you'd need ten feet, just a couple feet at the battery bank and a couple feet at the inverter.


Exactly the info I need. I'll hit them both with 4/0 then.

As for the ground location, there really isn't a good spot on the frame extensions at the rear of the coach to attach a ground, and there is already a ground bus bar near the battery box that I was going to bolt it to (where the factory generator ground is, among other things. I will then add another 4/0 from the bar to the battery bank in conjunction with the 2 awg that already grounds to the battery. This should fix the issues you noted, with the 4/0 carrying the main load and the 2 awg carrying all the little loads from the 12v appliances.
Resurrecting an inherited 1980 Minnie Winnie 20RG from the dead after sitting since 1998..

DrewE
Explorer
Explorer
DRTDEVL wrote:
4/0 is 0.46"
2 awg is 0.2576"
2x 2awg is 0.5152"

I believe this will pass the same, if not more, power capacity, while saving money. After all, 4/0 cable is about $4/foot and 2 awg is less than $2/foot. I'll need about 10 feet each for the positive and ground, so this is the difference of $20 in cabling for the same capacity.

Unless I am wrong, then someone correct me. I don't want to burn the thing down.


It's not the same, for a couple of reasons. First, you're comparing diameter rather than cross-sectional area, which of course for a round wire is pi r^2. Here is a nice chart where the math is done for you; 2 AWG has a cross-sectional area of 42.4mm^2, and 4/0 has a cross-sectional area of 107 mm^2. Two and a half 2 AWG wires would be just about equivalent.

The second reason they are not equivalent is perhaps of greater importance. If one of the ground wires were to work lose or break or corrode and have a (relatively) high resistance, you may never notice the difference in performance but the one remaining good one would carry most or all of the current and be overloaded. Even under good conditions there is likely to be some current imbalance as the impedances will not be precisely equal, and it doesn't take very much resistance at all to cause a fairly significant difference for a chunk of wire.

Can't the grounds connect to the trailer frame itself? I wouldn't think you'd need ten feet, just a couple feet at the battery bank and a couple feet at the inverter.

DRTDEVL
Explorer
Explorer
4/0 is 0.46"
2 awg is 0.2576"
2x 2awg is 0.5152"

There is already a 10' run of 2 awg in place for the ground from the factory. I will be pairing this with a second 2 awg wire, for a total of 0.5152" thickness for the ground, as opposed to the 0.46" thickness of the 4/0 positive. Both grounds will go to the chassis ground bar, and a second 2 awg will go from the bar to the batteries.

I believe this will pass the same, if not more, power capacity, while saving money. After all, 4/0 cable is about $4/foot and 2 awg is less than $2/foot. I'll need about 10 feet each for the positive and ground, so this is the difference of $20 in cabling for the same capacity.

Unless I am wrong, then someone correct me. I don't want to burn the thing down.
Resurrecting an inherited 1980 Minnie Winnie 20RG from the dead after sitting since 1998..

DrewE
Explorer
Explorer
You should put the same size cable for the battery ground and inverter ground as the positive cable. Every electron that flows through one path must eventually flow through the other one.

(Alternately, you could fuse the positive lead for the maximum safe carrying capacity of the smaller ground leads, I suppose; but that would limit your inverter output probably more than you wish.)

DRTDEVL
Explorer
Explorer
Well, I got a deal on a pure sine wave 2500w (5000w peak) inverter with remote, so I reduced the capacity a little. Otherwise, I'm forging ahead as planned: Install RV outlet at junction in power cable box, wire inverter to other end in the generator bay, install a 4/0 positive cable to inverter with the 100a breaker, install a second 2 awg chassis ground and a second 2 awg cable from the battery negative to ground, and replace the single group 24 battery with a pair of group 31 batteries (giving 210 aH compared to the current 95 aH).

I also discovered that a new power center will be easy enough to put in this year, with a 3-stage charger/maintainer and all the 12v circuits to go with the 115 vac output main breaker as my current setup has. I just need to check the amp ratings and size measurements I need when I pull it back out of storage Friday to determine which panel to order.
Resurrecting an inherited 1980 Minnie Winnie 20RG from the dead after sitting since 1998..

MEXICOWANDERER
Explorer
Explorer
Regarding a rebuilding shop "hopping up" an alternator

No rebuilding shop rewinds their own alternators

Therefore they have to rely on what their supplier offers

Replacement stators use laminations that have had the old wire burned out of them

Nothing is free in the alternator hopping up department

Change a WYE WOUND revised 78 amp squareback stator to a DELTA WOUND

And top end output may jump from 78 to 110 amperes

And midrange maximum may drop from 50 to 30 amps

While at alternator speeds of 3,000 and below there will be zero output

And it helps to keep in mind with alternators of 90 amps or greater double 15/32" belts or greater must be used. There exists no serpentine belt pulley.

See if you can find a 4091460 117 amp alternator, and brackets at a wrecking yard. At lower speeds this alternator may develop 85 amperes while a revised squareback sruggles to make 20 amperes. The 4091460 is a tough unit.

Matt_Colie
Explorer
Explorer
Wow Drt,

This is rewarding.
It is really rare that we get a new person with an old coach that has a good plan. (Replacing the 16.5 rims was a real good start.)

The only caution I would put in your current plan is that the quiescent load of the 3K inverter could be a lot more than that for a smaller device. And everything else gets smaller (cheaper) as well.

And I bet you are doing everything like you are going to have to be the next person to work on too.....

Matt
Matt & Mary Colie
A sailor, his bride and their black dogs (one dear dog is waiting for us at the bridge) going to see some dry places that have Geocaches in a coach made the year we married.

DRTDEVL
Explorer
Explorer
I still have the original alternator (only 23,400 miles on it); I'll have to pull it out and check. Perhaps I can get a local electrical shop to repair it and boost it up a bit?

I figured out the generator prep kit wiring. I pulled the back seat and lower panel and traced it back to the shore power cable box. I went into the power cable box, and, lo and behold, another junction box. All I need is to wire in a 30a receptacle on the one side, and wire the other side to the inverter. This means no problems with switching, since I will plug into the inverter power when driving down the road or boondocking, and into the park hookups or generator when not.

Now the next part is the cables. It was only one, and its the negative, not the positive. I also think its only 2 awg. I'll have to get a second 2 awg cable to ground to the chassis (one 2 awg to battery, one to the frame) and a 4/0 positive cable from the welding supply store and make the cabling legit. I'll also pick up extra lugs to make the 2 awg cables between the batteries. Eventually I want to add another battery tray and mount a couple more, but I am limited to two this year.

For now, I'll have to leave the original power center box in, as it contains all the 12v fuses, the 10 breaker, and the charge sentry. Maybe next winter I can make that a project list... put in a small breaker panel, a modern converter/charger, and a separate 12v fuse panel, all while finding a way to make it fit behind the original cover.
Resurrecting an inherited 1980 Minnie Winnie 20RG from the dead after sitting since 1998..

MEXICOWANDERER
Explorer
Explorer
I know the alternator isn't the greatest, since the largest factory internal fan alternator for these coaches is 60 amps. I do want to measure and upgrade to an external fan unit, that way I can get a decent 160+ amp unit in there (yes, I will replace the charge wire, too).


The most powerful OEM direct-fit alternator meaning drop-in like the original is not a 60-amp. More than likely unless it was sacrificed as a core for an earlier model alternator your unit "had" a MODIFIED SQUAREBACK alternator. This 1980's alternator has a 78 amp model.

Might be hard to find these days but the 1980 Mopar had an optional 117 ampere alternator Mopar # 4091460.

Here is what a modified squareback looks like



See how the front and rear case halves almost touch? Now look at the earlier model squareback that maxxed out at a 60-amp model



There is an even earlier model use the wayback machine to vizualize




  • Dodge motorhomes had terrible issues with the original wiring for the charging system
  • Forget how the rig is wired to charge the battery. The firewall plug is far too pitiful to pass even chassis electrical loads
  • Drill a hole alongside the main bulkhead plug. Use a length of TEN GAUGE wire to splice into the outer and the inner main red power wire
  • The house battery bank needs it's own dedicated cable which does not pass through the firewall
  • The voltage regulator is pure garbage. Use a Bosch type relay to feed direct power to the sense/power lead into the reg. Way too much resistance and volt drop using the original circuit that powers on and off through the rig ignition switch
  • Common to see 15.8 volts at the alternator terminal 15.2 volts at the battery post. This will boil the snot out of all batteries on the rig
  • This fix is not optional. Some folks who disbelieve these fixes have to learn the hard way. a sad and bitter lesson.




Use a RELAY and BATTERY power for replacing the existing field ign feed wire and the voltage regulator (top) Ign wire

DRTDEVL
Explorer
Explorer
time2roll wrote:
OK at least fuse the generator start cables with maybe 120 amp fuse.
Assuming it is #4 wire.

Often start cables are not fused but that inverter could melt the wire if the wrong thing gets turned on such as a microwave that pulls 160 amps.


This is a no-frills coach. There is no microwave on board.

And I have a 100 amp breaker to put inline.
Resurrecting an inherited 1980 Minnie Winnie 20RG from the dead after sitting since 1998..

DRTDEVL
Explorer
Explorer
jkwilson wrote:
DRTDEVL wrote:

As I answered in another post, I won't be running this hard. Its for reliability that I will be getting an inverter of that size. I am pretty sure it will run fine on 2 batteries with my setup, since it will usually only be drawing 150w continuous, with the occasional heavier load. Yes, its sine wave.

This model has a junction box in the generator bay with 4 wires, no way to plug the main cable into it (opposite side of RV). I'll check the routing when I pull the back seat panels and see what's going on.


150W output will be drawing 10A or more out of the batteries. Battery life isn't going to be what you are expecting. My off-the-cuff calculation would be 15 hours at best. Inverters are generally only practical for an hour or two of TV watching in the evening after a day on the road unless you have solar panels or a generator to recharge the batteries every day.


We only use the TV during passing rain showers, otherwise we are outside. After all, that's the point of heading into the woods, right? The only "continuous" load would be the mini-fridge at 96 watts.
Resurrecting an inherited 1980 Minnie Winnie 20RG from the dead after sitting since 1998..

DRTDEVL
Explorer
Explorer
DrewE wrote:
I would guess that there is some sort of a transfer switch arrangement, either an automatic transfer switch, some sort of manual switch (which would probably be incorporated into the AC electrical panel and have more or less clear instructions printed on it), or a socket to plug the shore power cord into that connects to the generator.

Do not hook anything up that relies on you remembering to disconnect the inverter before plugging in. Any such arrangement I can think of would be unsafe and not up to electric codes. Most leave the shore power cord disconnected but energized, for example, which is problematic in itself; a bit of loose metal or a misplaced hand could come into contact with it. If you're at all like me, too, you'll at some point or another forget and cause a fried inverter or similar.

As others have said, a 3000 watt inverter demands a very substantial battery bank. Many of the cheap inverters available have rather optimistic ratings (to put it kindly) and do not take well at all to being driven hard for very long.

What are you interested in powering with the inverter? How much power do you really need, and for how long of a stretch? If it's a lot, it may make more sense to purchase a generator, preferably an inverter generator...or to rethink your electrical usage (e.g. make coffee on the stovetop rather than with an electrical coffee brewer).


I already have a 3600 watt (500 peak) generator that I can use when necessary, its just a portable one on wheels rather than an on-board one.
Resurrecting an inherited 1980 Minnie Winnie 20RG from the dead after sitting since 1998..

time2roll
Explorer II
Explorer II
OK at least fuse the generator start cables with maybe 120 amp fuse.
Assuming it is #4 wire.

Often start cables are not fused but that inverter could melt the wire if the wrong thing gets turned on such as a microwave that pulls 160 amps.