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What appliances can I expect to run with my 12v system?


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Ok, I've read everything that I could get my hands on regarding house batteries and 12v systems. I'm currently living full time (as of October 27) in a 1992 Mallard Sprinter that I bought used off of Craigslist. I have attended the Escapees Bootcamp, and thought that I had gotten my answer, but now I'm confused again. Should I be able to charge my phone in one of the 110 outlets from the house batteries? Or will they only run the 12v lights?


I have no RV experience, and I'm not super handy when it comes to home/auto maintenance. I'm trying to learn, and forums have been super helpful.


My basic question is: what can I expect to run off my house batteries? The reason I'm asking is because I've had quite the adventure trying to make sure that all of my systems were working properly, and some have influenced others, as you can imagine. When we first purchased the coach, the owner walked me through the systems, and I figured that it was mostly all common sense. I may have been a little starry eyed at the idea of finally finding a rig in my price range, available in the timeframe in which I required it. So everything *appeared* to be working. Once we hit the road, we spent the first weekend at a state park with electrical and water hookups -- learning how all that worked the first time was easy. Even had no issue dumping black and gray water the first time.


Then we finally hit the open road, and had to spend one night in a Walmart parking lot. Much to my surprise, nothing seemed to be able to run off the house batteries. No lights, no water, nothing. To further complicate matters, I couldn't get the generator to start. So I thought there was an issue with the genny, and made an appointment to get it looked at. We continued our trip, confining our stays to places that had hookups. Over the course of time, and online research, I read that the engine alternator should be charging the house batteries, as well as shore power. Since we've been driving for a week, and hooking up to shore, I thought that the battery MUST be charged, and tried it again. No luck, but on a whim I tried to start the generator again. Chugging for a bit adn then VROOM it starts!


Scratching my head and shrugging my shoulders, I cancel the appointment to have the genny looked at. It has not been a problem since, but I still don't understand the battery situation. It appears to be new, but I haven't gotten it tested yet. I'm far from home, and not even sure where or how to get it tested. An RV tech checking out my furnace touched it with a 12v tester and it lit up, so I'm guessing there is power in there.


I should mention that the panel of lights that shows the charge level of the battery, as well as the fill level of our tanks is also on the fritz. When plugged into shore power, it shows the battery at full charge, but the moment we unplug it shows "L" which I'm guessing means Low = discharged.


Sorry this post got so long, I'm hoping someone out there will take the time to read it and answer my question. Will the plugs in the rig work off the batteries? or only while plugged into shore power or off the generator?

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Interior lights, water pump, and furnace controls & blower all run on 12VDC. When plugged into shore power a 120VAC to 12VDC converter supplies 12 volt power and also charges the house battery(s). Since nothing works unless you are plugged in this means the house battery is either not connected to the system or it is dead, or both. Do the interior lights operate when the engine is running? They should because the engine alternator is a third source of 12VDC.


On edit: Unless you have a built-in inverter the 120VAC outlets will only function when supplied by either shore power or the generator.



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First thing is to check then house battery condition as the water level may be empty, battery maybe bad, not hooked up or there may not even be a house battery in the RV.

Then if that all checks out there is probably a auto reset relay that is bad in the 12 Vdc circuit that is not letting the house battery charge. 5 to 10 dollar part at a auto parts store. Maybe even Walmart would have it.

While there buy a cheap electrical meter for testing the system.

As for the size of auto eraser breaker, you need to replace it with them same size.

With the meter you can test the system to find the problem.



Safe Travels, Vern

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Do the interior lights operate when the engine is running? They should because the engine alternator is a third source of 12VDC.


Interesting - My alternator does not charge the house battery - The systems are isolated and only interconnect if I hold in the emergency start button.


Is it normal for the systems to be interconnected so that the alternator charges the house battery while driving? If so how is that done without draining the engine battery? If by a diode isolater, which battery does the alternator sense? (ie how do you prevent overcharging of the non sensed battery?)

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If you engine alternator is not charging the house batteries while driving there is probably a relay that is not passing current to the house batteries.

A volt meter would help following the the power circuit to see where th problem is. There could be something else, but a volt meter would be very helpful as to find your problem




Safe Travels, Vern

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On charging when plugged in. You're converter is receiving power from shore power and is sending a charge to your batteries. We know this because your led panel is showing "Full". That doesn't mean your battery/ies are full however. It's just reading the charge being produced by the converter. When you unplug the converter switches off and is reading "L" because it is only detecting the charge level of the battery/ies themselves. Just because it is reading "L" does not necessarily mean a whole lot since those panels are highly inaccurate.. especially a 16 year old panel. Take it with a grain of salt and use your voltmeter to check the battery/ies.


Truck alternator charge to batteries. It is not a given that a charge is being sent from your alternator to your trailer battery/ies. Some trucks have that capability but may not have the relays and fuses installed to do so (it's, generally speaking.. in older model trucks, not "standard" to have the relays pre-installed). Check the plug at the rear of your vehicle with a voltmeter. Also be aware that even if your truck is providing 12v to your trailer, it may only be sufficient enough to help maintain the current state of charge, but not adequate enough to actually increase the charge level.

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Does your rig have a battery disconnect switch and if so, is it on? Check the battery with your voltmeter to see what you actually have and take a look into the cells to see is there's water in each. If the tops of one cell or more is exposed, you should replace your batteries. While checking voltage take a look at the before and after readings when you plug the coach in vs. not plugged in. Readings should be higher when plugged in which would indicate the converter is working. Then do the same with the engine. Unplug the coach and take a battery reading, then start the coach and check it again. If the voltage increased with the engine running you know it will charge going down the road. An alternative to check the battery condition would be to take it/them to any auto parts store and have it checked. They'll tell you if its bad.

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First of all, welcome to the Escapee forums! Since you are also new to the Escapees RV Club, let me also welcome you to it as well! We are very happy that you have chosen to join us and we will do our very best to assist you and address your difficulties.


Let me warn you that this is going to be a pretty long post but I will try to explain a few things and perhaps help you figure out what you need to know. Looking at your profile it states that your Sprinter is one of the Class A versions but some things may vary depending upon the chassis yours is built on. You might also share with us where you are presently located as there could be someone nearby who could help you to get things figured out. If you happen to be anywhere close to Tyler, TX just let me know and I'll arrange to stop by and help you work through this.


There are a number of things that are pretty standard to all class A RVs. There are always two electrical systems of 12V-dc and a third one that is of 120V-ac. The 12V systems are one for starting the chassis engine and the other for supplying the RV side of things when the engine is not running. There should be one battery located near the engine that powers the starter and all of the usually automotive circuits. There is also an alternator that supplies power while the engine is running and which recharges the chassis battery while driving.


The second system is the coach 12V system and it should have 1 or 2 batteries to supply it. Those batteries can be charged by the chassis alternator when the engine is running but the power is supplied by a solenoid device which connects the two systems once the chassis engine is running (assuming that it works properly) and then it opens to prevent the coach loads from running down the chassis battery when the engine is not running. There is also a converter which takes 120V-ac power and converts it into 12V-dc to recharge the coach battery and supply the coach loads when connected to shore power or when the generator set is running. The 12V side of the coach is the power to the lights, water pump, refrigerator controls, furnace blower & controls, water heater controls, and most appliances except the microwave and probably not the TV. A critical part of this system is the coach battery or batteries. That battery should be a deep cycle battery and it's proper maintenance is critical. I am guessing that your coach battery is not in good condition, so the first thing I suggest is that you check the electrolyte levels and be sure that they are at proper levels. With an older RV there is a very good chance that your batteries are not in good condition and may need to be replaced. At this point I strongly suggest that you take some time and visit the website of Mark Nemeth and read his 12V side of life, parts 1 and 2.


The last electrical system of your RV is the 120V-ac which supplies the microwave, alternate power to the refrigerator's heaters, all of the outlets in the RV, and probably the TV and CD player if you have one. This system has 2 sources that can supply it which are the shore power cable and the generator set. You probably have an automatic change-over device to shift between the two sources, but you may have an outlet in the cord storage for shore power that you plug it into to supply 120V. Never shift power sources with large loads in operation or that auto change-over will fail in time. The 120V from either source supplies power to the converter that was mentioned above to supply 12V and to recharge the coach batteries. Coach batteries supply power to the starter for the generator set. There is a small chance that your RV has an inverter/charger in place of the converter, which could supply limited 120V-ac from your batteries, but that was not standard for your coach so it probably isn't there.


Then we finally hit the open road, and had to spend one night in a Walmart parking lot. Much to my surprise, nothing seemed to be able to run off the house batteries. No lights, no water, nothing.

This is part of the reason that I suspect that your coach battery(S) need to be replaced. I suggest that you have the coach battery load tested which can be done free at most battery selling businesses or parts houses. Before you do this take the caps off of the battery and see if there is liquid in each cell that comes just to the bottom of the tube inside of each. If you can see the top of the battery plates, it is dry and distilled water must be added to bring them to the proper level. If the battery does need to be replaced, make sure that you get a true deep cycle battery and not a starting battery or a marine battery. They are three different batteries. A deep cycle battery is also called a golf cart battery.


To further complicate matters, I couldn't get the generator to start.

Somewhere on the dash there should be a switch called "emergency start" or some similar name and it's purpose is to cross connect the batteries between the chassis and the coach to allow the use of both to either crank the chassis engine or to do the same for the generator set. When the generator will not crank, first start the chassis engine and let it run for 5 minutes or so, then hold that switch down while you crank the starter for the generator set and it should work. You can also do exactly the opposite if the chassis battery is down and the coach battery is charged, but always start your generator first.


I should mention that the panel of lights that shows the charge level of the battery, as well as the fill level of our tanks is also on the fritz.

I suspect that the tank levels say full all of the time and that is pretty normal in older RVs. It is due to a coating of waste on the inside of the tanks and the cheap type of level sensors used. I suggest that we make the tank level indicators the subject of a different thread. The battery level indicator is also cheap and is only a volt meter that reads whatever is being supplied to your RV system. They are of very little use.


When plugged into shore power, it shows the battery at full charge, but the moment we unplug it shows "L" which I'm guessing means Low = discharged

This tells me that your converter is supplying the 12V power needed when you connect to shore power and that your battery is not. It probably means that your batteries need to be replaced, but could only mean that they need distilled water added to them. It is a good indication that you have a battery issue of some sort.


Will the plugs in the rig work off the batteries? or only while plugged into shore power or off the generator?

No. You must have 120V-ac power and it has to be supplied by the shore power cord or the generator set.

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Hey all! Thanks for the quick and thorough responses. There is a lot of information here, and I appreciate you taking the time to walk me through.


Kirk -- I actually was reading through The 12volt Side of Life when I asked my question! Mark is amazing, I met him at RV Boot Camp. He, like the rest of you folks on here, seems to have an infinite well of knowledge and patience, which is an amazing combination.


Looks like I've got a lot of learning to do!


Related question: How do I figure out if I have a converter vs an inverter? I'm assuming, based on the age of my rig, that I just have the standard converter. I had read about true sine wave inverters when the wife asked me to get solar panels installed. I don't think that solar will help us at this point, and we may need to just change our lifestyle. We are currently very dependent on our electronic devices and the internet. Knowing now that the outlets won't work off of shore power is a relief, if a little disappointing.


Thanks, again, for all the help, y'all!

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There are a number of ways to determine if you have an inverter. In most cases the device is actually a charger/inverter that does conversion both directions and supplies 12V power when 120V is available and supplies 120V power when it isn't available(drawing from the batteries). The first place to look is at the converter, as it will say on it somewhere what it is. Another hint is the number of coach batteries that you have since an inverter will discharge on or two batteries very rapidly and is seldom installed with fewer than 4 batteries(but can happen). The fact that none of your 120V outlets work when you do not have shore power or the generator set running is another indication that you do not have one. I am sure that your RV didn't have an inverter from the factory so if it does it would have been added by a previous owner. In such a case, there is also usually as second 120V distribution box that is small to handle the output of the inverter. If you did have one, it is a high probability that the seller would have pointed it out since that could be a strong selling point. Were it me, I would not spend a lot of time looking for one if none of these indicators are there since it is very unlikely that you do, unless there are at least 4 coach batteries. I'd spend the time learning about what we know that you have as that knowledge will soon discover the inverter if it is there somewhere.


I had read about true sine wave inverters when the wife asked me to get solar panels installed. I don't think that solar will help us at this point, and we may need to just change our lifestyle. We are currently very dependent on our electronic devices and the internet.

If and when you do begin to add such items, the increase in cost to use a true sine wave inverter as compared to any other quality one is easily justifiable. The little, inexpensive inverters that can be found everywhere are find for a small, single device power supply, but not at all satisfactory for a permanent installation. But remember that your battery can only supply a nominal 12V-dc and in order for it to supply 1 amp of power at 120V-ac the battery must supply slightly more than 10 amps of 12V electricity. The voltage is raised by using more current. The rule is that the measure of actual power used (watts) is determined by multiplying the voltage by the current so 120V electric power requires 10 times as much DC current into an inverter to supply it, thus you need to add batteries first.


A major catch here is that your coach probably has a GVWR of somewhere around 16000# and to live in it you are probably already at or near that maximum weight(if not over). Each additional battery that you put in will add around 50# of additional weight as well as taking up significant storage space. Add to that the fact that with the addition of equipment to most RVs you are very unlikely to ever get much of your investment back when you sell or trade up, so money spent on upgrades is just gone. This is especially true for older RVs. If you should spend several thousand dollars in improving things in the RV you have now, you need to do so thinking of the value that you will get from it because you that might make your RV more easy to sell at some future time, but you won't recover the money spent.


I suggest that because you have very little RV background, you should first explore the lifestyle with what you now own and managing with the things it has, while you learn just what way that you and your spouse enjoy. Things like solar power, extra batteries and inverters may be nice, but the majority of RVs never have them installed. Only those who spend a lot of time living off of the grid ever really justify the work and money involved in such additions, especially to an older RV. We lived in our RV for more than 11 years (a 1998 Cruise Master, Ford chassis, 36' with no slides) and we never added any of those things. We spent very little on camping sites because we enjoy doing volunteer work at wildlife refuges, historic sites, state & national parks, and even an occasional campground host position and so we were supplied a full hook-up site in return for a few days a week of volunteer service. We loved that way of life and still participate in it when time and health allow, having spent 5 months in our 20' travel trailer in 2014 as campground hosts in South Dakota. If budget concerns are the primary reason you are thinking of living off grid, then take a look at the RV volunteer lifestyle before you get too far as many of us here find it to be a wonderful and fulfilling way of life. When we were traveling we did at times spend a night without hook-ups with our two batteries and a generator set for our only power. We also used the Escapee's "Stopin Spots" at times and made more than a few new friends in the process. And if you are 62 or more you can get your Golden Age federal parks card and get 1/2 price in their campgrounds or use Passport America to get 1/2 price in commercial RV parks. On our website we have posted the last 5 years of expenses that we had and while some things have risen since we left fultime in 2011, it does show that we spent very little on RV sites, yet were never serious boondockers. There are many ways to travel inexpensively.


As to Mark Nemeth, I first came into contact with Mark back in the late 90's when he was on the road, fulltime in a fifth wheel and traveling all of the time. We first met in person at Rainbow's End about the time that he started to work for Escapees. We have socialized when we cross paths ever since that time and we have shared a lot of RV information as well as a few stories and more than one social time. Mark is a pretty unique fellow and a very good friend. He is an RVer's, RVer. :P

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Another welcome to this wonderful forum.


You first asked:


"Should I be able to charge my phone in one of the 110 outlets from the house batteries?"


You might need to rethink how you lived at home and now in the RV. The phone wall charger at home takes 120 volt AC, and converts and reduces that power to some very small amount of DC volts. Instead of thinking that way, just get the 12 volt plug cords and use your dash 12 volt outlet.


People do the same thing with CAP machines, as they are low volt DC units, and so they sometimes can be run off the coach house batteries.


Doing either often removes the need for an inverter to step up from 12 volt to 120, and then back down with the phone or CAP transformer.

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A couple of 'general' comments that may help.


First inverters weren't a common feature in RV's until about mid to late 1990's. Then mostly on higher end RVs. So a 1992 unit is unlikely to have one unless installed at a later date.


Converter takes 110v and 'converts' it into 12volts. (Transformer). Yes I know there are exceptions!

Inverter takes 12v and converts it back into 110v.


As a general rule anything that produces heat will struggle with 110v from an inverter.


If 'all' you want is to charge phones, computers etc then a simple generic charger from someone like Best Buys will do most of your charging from your 110v outlets.


Whole books and web sites are devoted to this subject. It can get very complicated and opinions will vary markedly as to which is the best way to go. If I were you I would find a 'good' dealer who knows electrical systems, (no I'm not being funny), and ask them to go over your system and give you some advise.


We had a fully electrical bus conversion with a 'controller' that done my thunking 4 me. That's my answer to complicated and frustrating systems.


good luck.

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