Help me upgrade my 1982 Converter and assess my situation?

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Hey everyone, new to the community and RVs and introduced my 1982 Chevy Citation 19’ Motorhome in the welcome thread.

So among other things, I’m thinking it would be a good idea to replace my original 1982 System Monitors Inc MRM 3000 converter. But I’m not sure where to start. I do not have an inverter either, so I’m pondering a combined unit. Specs are:
Input: 120 V 60hz and 55 amp AC
Output: 12V DC 30 Amp with 5 amp charger

Ill attach pics of everything below.

Can all you fine, smart folks help me formulate a plan on modernizing?

We will be using it a couple times a month from May till October or so, we are in Alberta and don’t plan on winter camping at this point. Probably a mix of camping with full service sites and no services. We have AC, furnace and water heater. 46 lb propane tank underneath for fridge, range, furnace and water heater. We have a small tv and would have some small items plugged in occasionally.

Not sure what else to add, I can provide whatever info is needed to help.

Thank you.
 

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John From Detroit

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Thouse big heavy transfomers = Lots of scrap metal


Replace/upgrade non-inverter Progressive Dynamics 4600 likely the smallest (I think that's a 4645) will do for your setup less you greatly expand battery bank.

Inverter/Converter.... Alas since I did my research product quality has changed so I won't recommend a make/model.
But note that you will have to upgrade your battery bank for anything over a few hundred watts.
 
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Thanks for the reply, I will look into that converter.

How much greater would you say my battery bank should get to consider getting a converter/inverter combined unit? Or even a more powerful converter?

I have the one in the engine compartment and 1 12 volt in the house. I was considering buying a new one for the engine compartment and moving that to the battery bank.

Would even having a smaller inverter, say 400 watt be worth it in my setup?

What would be the ideal way to update my situation?
 

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Larry N.

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Personally I'd not move the chassis battery to the house, since it's optimized for starting and won't do a good job sustaining the house. And with only one house battery I'd forget the inverter.

Just as an example, my Ventana has a 2000 watt inverter and the house battery bank is eight 6V batteries (wired to give 12V, of course), each with over 200 watt hours capacity. My previous rig (a Beaver) had a 2800 watt inverter and four huge 12V batteries (each twice the size of my current 6V units).

Each of the above needed recharging after running strictly on batteries overnight. However both rigs have a residential fridge, but also have lots of other things drawing juice from the batteries.

You could use a 400W inverter for a short time, depending on what you're trying to run, but a second house battery would be a big help.

If you go to the RESOURCES button near the top of the page you'll see articles about adding batteries (and much else, too), and they have information for download. Here's one of the links: https://www.rvforum.net/resources/adding-batteries-to-your-rv.185/
 
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Thanks for the reply. I did see the guide and it is very helpful and will come in handy.

Ok I’ll note that, so I’d be better off with 6v batteries than 12v that are not starting batteries like for the chassis? Would another 12v deep cycle to go along with my current one be good for the battery bank to run a smaller inverter?

Also, do you think a battery charger is a must own as a separate item?

Maybe just upgrading my converter to a newer one and adding another 12v deep cycle battery to the bank, plus a smaller inverter would be a good start?
Or newer converter/inverter instead of a seperate inverter?

Still learning and the electrical side will be the biggest learning curve.
 

Matt_C

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Clark,

First this to know is that if you parallel batteries that are not IDENTICAL, it will not go well....

Next thing what you posted a picture of is something I have not seen in years and had hoped to maintain that record. Before the current era, that was used to provide DC at a usable current and not over charge the house battery. It does this by separating the two. So, it barely charges the house bank (that battery doesn't mind and will take its time) and provides an unregulated 30amp supply to run the house side when there is shore power. Time to get a good one.

The next thing you need to do is start making a list of how much DC power you expect to need.

When you come back with that, then we can effectively guide you to a successful house DC system.

Matt
 
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Thanks very much!

I will put more priority to getting a new converter and just start there. I’m looking at a few but still trying to nail down exactly what I need and that will fit in the space.

Larry suggested one above im looking into and I looking at some others from online.
Just want to be sure I buy the correct one the first time.

Also DC list in progress at home, I can post it later. It’s not gonna be a huge list so that should make it easier.
 

Gary RV_Wizard

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No need to get hung up on 6v vs 12v - the reasons for choosing 6v golf car batteries are a potentially lower cost per amp-hour of capacity, and even that is based on some assumptions that may not apply to you. But you do want a deep-cycle design battery for the house, not an automotive starting battery. Any deep cycle design will last longer in that type of usage. Please read my magazine article of Choosing an RV Battery - it's in the RVForum RESOURCES library at https://www.rvforum.net/resources/choosing-a-battery-for-your-rv-v4-01.65/

You apparently have a single 12v battery now, so adding a second like it would double the time you can operate without recharging. Your furnace fan sucks a lot of 12v, but the circuit boards for fridge and water heater do not. On the other hand, if you don't have shore power and want to use an inverter to power 120v appliances, you will probably need a LOT more battery capacity. 4x12v deep cycles typically provide 75-120 AH each; 6v GC2 batteries provide about 200 AH per pair, so it works out about the same per battery. 12v deep cycles or marine/rv hybrids come is several different sizes and shapes, so may fit your physical space better. 6v GC2 batteries come in different heights but the same footprint. Choose the type that fits best with your physical layout and AH needs.

The converter should be sized to handle the size of the battery bank. a 45-50 amp converter will do for typical 1-2 battery set-ups. If you add more battery capacity, then 60-70 amps is a better choice.
 

Larry N.

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Ok I’ll note that, so I’d be better off with 6v batteries than 12v that are not starting batteries like for the chassis?
No, as Gary said, don't get hung up on 6V vs 12V. I gave examples of 6V on the Ventana and 12V batteries on the Beaver, and all are deep cycle batteries and do fine for the task. Again, as Gary said, a pair of 6V will probably be cheaper than a pair of 12V (volume production), but other than wiring them different, either way will work fine. DO read Gary's article.
 
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No need to get hung up on 6v vs 12v - the reasons for choosing 6v golf car batteries are a potentially lower cost per amp-hour of capacity, and even that is based on some assumptions that may not apply to you. But you do want a deep-cycle design battery for the house, not an automotive starting battery. Any deep cycle design will last longer in that type of usage. Please read my magazine article of Choosing an RV Battery - it's in the RVForum RESOURCES library at https://www.rvforum.net/resources/choosing-a-battery-for-your-rv-v4-01.65/

You apparently have a single 12v battery now, so adding a second like it would double the time you can operate without recharging. Your furnace fan sucks a lot of 12v, but the circuit boards for fridge and water heater do not. On the other hand, if you don't have shore power and want to use an inverter to power 120v appliances, you will probably need a LOT more battery capacity. 4x12v deep cycles typically provide 75-120 AH each; 6v GC2 batteries provide about 200 AH per pair, so it works out about the same per battery. 12v deep cycles or marine/rv hybrids come is several different sizes and shapes, so may fit your physical space better. 6v GC2 batteries come in different heights but the same footprint. Choose the type that fits best with your physical layout and AH needs.

The converter should be sized to handle the size of the battery bank. a 45-50 amp converter will do for typical 1-2 battery set-ups. If you add more battery capacity, then 60-70 amps is a better choice.
Thank you for all the resources you made, they are very helpful.

With that said, I will keep my single house battery for use for now, as that one I have is a deep cycle Napa 31rvs 12 volt. It tests fine at 12.3 right now. I could always pickup another of the same should I desire to move to 2 batteries.

Ive stayed in the motorhome the last couple nights, going through some basics of what we would use as far as electric goes. Honestly our needs are not very great at this time:

Fridge runs on propane and while I’m not exactly sure, electric use is minimal.
Water heater will not be used unless at full service sites.
Furnace is propane and while I’m not totally sure of power usage, we won’t use it a lot.
AC is only for when on shore power.
Range is propane.

Plugging things in, mainly just a couple iPhones as needed and an iPad. Since we most likely won’t have wifi or cell service most of the places, mainly just charging and using for music, books and movies.
There is a tv but we aren’t big tv people anyway, so it will either be removed or used very little. It’s a small little DVD built in one.

The rest is just lights. Led stuff plugged in for the outside.

Thats all we have listed right now. As we were tent campers before and will still have a fire and use it, not too many big needs yet for electric.

So that brings me back to my converter. The more I’m reading and the advice of some here, leads to me still thinking it best to replace the converter to start. To give better battery optimization and just a safer source of power, since this one is so old.

Just still trying to figure out what will be the best option.

Progressive Dynamics 4655 seems like a good bet and looks like it should connect and fit right in the housing space.
Local RV place parts department suggested the WFCO WF 9855 deck mounted one but it was info passed on and the parts person couldn’t explain further. What is the difference between deck mounted the above PD one?

Would it make any sense to replace the whole power center?

The more I read into how to find the best replacement, since mine is so old, the more confusing it seems.

Am I on the right track with the above options?
 

Larry N.

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As we were tent campers before and will still have a fire and use it, not too many big needs yet for electric.
I don't know what the fire situation is in Alberta, but a large part of the western U.S. is dry and there are numerous fires all over the west. As a result, many jurisdictions are clamping down on fires, some not allowing fires even in metal fire pits, so you might check on that before depending on having a fire at your campsite(s).

I will keep my single house battery for use for now, as that one I have is a deep cycle Napa 31rvs 12 volt. It tests fine at 12.3 right now.
12.3V is somewhat discharged on a good battery -- 12.6V shows a full battery. Of course it also depends on what load (if any) you had when measuring and on where you measured, as well as how long after stopping the charging. So perhaps you'd want to check out https://www.rvforum.net/resources/battery-charging-basics.112/ for some good info on the charge state.
 
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Ok so I’m looking to pull the trigger on getting the upgrade on the converter.

After it was posted, it seems like the Progressive Dynamics PD4655 should work. Can anyone help me confirm that this should work? My buddy who is an electrician will help install but he is not an RV guy but he said he’s confident he will have no issues?

In my first post I put up pics, I should stick with 55amp and not exceed that correct?
 

Gary RV_Wizard

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The NAPA 31RVS is a marine/RV hybrid deep cycle, so marginally better than a starting battery but not a "true deep cycle". Should work fine for a few years.

The converter you are replacing has a max 30A output, so I'd suggest the 45A PD4645. That's a big step up from 30; 55A would be real overkill. The physical dimensions are probably different, so you will have some mods to do. Repalce the wiring between converter and battery to handle the 45A potential charging current.
 
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Thank you for that info, that is helpful. I was reading the input and output in the wrong way, thinking I’d need the pd4655 based on my 55amp input and not the 30 amp output.
Honestly didn’t think of the need to change the wiring to handle the difference from 30 to 45amp. Thanks for pointing that out. The RV guy didn’t even hesitate when I showed him my old one and said easy swap with a 55amp one.

The size difference I’ve been wishing I could see more in person to compare. The space the current converter takes is about 12” wide x 6” tall x 7” deep, give or take an 8th or 3. The whole power center is 17 1/4 wide x 11” tall x 7” deep.

Guess I need to keep planning this upgrade out.
 

Gary RV_Wizard

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The RV guy didn’t even hesitate when I showed him my old one and said easy swap with a 55amp one.
Everybody loves an optimist! The PD4600 series is designed to easily replace Magnetek 6300, Parallax 7100/7300, and WFCO 8900 models. It should work for other similar units, but maybe not so easily as the others. I'm doubtful it will slide right in your as it does with the other brands. It may be just as easy to place a deck-mount converter along side it somewhere and simply bypass the old converter. I'm just guessing; it would depend on the dimensions and physical layout of what you have.

Here's the 46xx installation manual.

Personally I'd replace the entire power center, including breaker & fuse panels.
 

Mark_K5LXP

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Since we're throwing some numbers around here are a few more.

I couldn't find a manufacturer data sheet for the Napa battery but it's shown as a 105Ah which sounds right. Most flooded batteries specify the charge rate at C10, so in this case about 10.5 amps would be the "recommended" charge rate. Some batteries spec as high as 20% so at that most liberal extreme, about 20 amps would be the most you've ever charge this battery at. So dropping a 45 or 55A converter on it would be soundly beyond the ratings of the battery. The effects of high charge rate is cumulative and based on the number and severity of events, (just as deep/hard discharges) so most don't pay much attention to charge rate. But it's there, if you care. Adding a second battery would split the charge current between both and cut it in half, a big number. But it doubles your battery cost so you have to decide what operational factors for your battery are important to you.

Wire gauge and length between the converter and the battery plays some role in this. Odds are the wiring intended for a 30A converter will be lighter than that intended for 45 or 55A. On the plus side the lighter wiring will reduce the high currents a bit, on the downside is the voltage at the converter, and the points it will switch charging modes, will be different than the voltages at the battery. So the battery will not benefit as much from the multistage charging steps from a modern converter as it would with a heavier gauge/shorter charging wire. Again, not make or break but cumulative over time, so as above that's a factor to consider if you care.

Point being is that there are different levels of "drop in replacement", you can install a new converter and it will "work" but depending on what other system factors you care about, it may not be "plug and play". This is a limitation inherent to the inexpensive converters that are on the market intended for an assumed application. One can buy more advanced converters/inverters with greater adjustability but at an increased cost which may not add value to to many applications, so it's usually easier to just pick a converter that gets you "close enough" and call it done. Odds are pretty good that even a "less optimum" installation with a modern converter will be nicer to the batteries than the transformer/rectifier battery boilers of days gone by, so one take on it might be to put something in and see if the result meets the need or expectation before refitting for "optimum".

Mark B.
Albuquerque, N M
 
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Thanks both Gary and Mark for those posts, some of it is over my head but I get the gist of it, I think lol.

I did start looking at some slightly older 35 amp converters last night. They are a bit cheaper and more in line with my current amperage of my old converter.

Mark I think you hit on what might more closely resemble what I want to do. Get rid of the old converter, as others have pointed out as well, to just be more efficient and safer. I don’t need the newest tech, just something that works with what I have and can keep me running safely

If I can just replace the converter instead of the whole power Center, plus potentially still replace that house battery with something better that should put me in a much better spot I think? And save some money.

But so many different converters keep confusing me what kind I should get and what will fill that need and fit that space.

Deck mounted ones look much different but I’m assuming they do the same thing but just have different mounting options?

I’m tempted to just call a local Mobile RV tech and get him to look at everything and size it up for me.

I don’t want to screw up the electrical and I don’t want to pay a fortune either lol

I appreciate all the input!
 

Mark_K5LXP

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My perspective on this at a practical level is don't let perfection be the enemy of good enough. I posted my reply here solely to illustrate that there's considerations to make when changing part of a system. Anyone that sells you a 55A converter to replace a 30A one, using a 100Ah battery isn't taking the system into account. You do get a reduction in charge time but at the expense of some battery longevity. Maybe you're OK with that, depending on how often and deeply it's exercised that may not be the predominant factor in battery life anyway. Or, a "properly" balanced system which does get optimum life ends up costing just as much or more in up front component expense. So depending on the performance you expect and what you're willing to spend sometimes "optimum" may not be the sweet spot in terms of value.

"Ideally" you'd change the power center out, upgrade the wire to the battery and double the bank size. That would give you a "typical" modern setup many folks are using with good success. What "ideal" is worth to you is another question. I too have an obsolete converter and am faced with the same prospect, so instead of a refit I rebuilt the old converter and changed the voltage a bit to be nicer to the batteries. But that's me, and I'm set up to do that kind of stuff. I'm having a tough time rationalizing replacing a working converter and batteries that are currently plenty for my needs for a "better" setup that ultimately will cost me hundreds of dollars and no net functional improvement.

I think where I'd go with this is decide on a battery bank size and buy a replacement converter based on that. You can buy 30A converters which would be more in line with the single battery there, or decide to bump up the Ah and go with a bigger converter. Assess the wiring and decide if that's something to address or leave alone. Otherwise if the power center that's there is working OK then maybe leave well enough alone and just focus on the converter update, driven by battery size.

Mark B.
Albuquerque, NM
 
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Well I believe I have come to a decision.

With the help of a very helpful local RV tech, I will be redoing the power center. Will use a PD9145 and up the amps a bit. Most likely will add a CharGE Wizard to go along with it.

Gonna keep the current single 12v house battery and see how it does, will budget for two 6v GC batteries when the time comes.

That should give me a good upgrade and I can assess after a few trips. Potential other upgrades would be solar and an inverter but will see if they are needed.

Everyone was so helpful and I appreciate the advice.
 
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