How I finally fixed my '96 Roadtrek cabin battery's charging issues

[VTPete]

The symptoms:
While parked, my cabin battery would drain over time despite having nothing turned on and the power shut off. Also, although the battery would charge while driving down the road, it never charged properly while on shore power.

This took a while (over a year) for me to finally figure out. In the meantime, I ruined at least one deep cycle battery because I had left the refrigerator on 12v for several days while being plugged into shore power. (That should not have drained the battery!)

In the end, there were two separate things wrong with my old '96 Dodge based Roadtrek 190 popular - and chances are they're wrong with yours as well!

First, the isolator under the hood of the vehicle was allowing my cabin battery to essentially drain while it was parked - both the cabin battery and van's starter battery were trying to find equilibrium and honestly, my starter battery is old. So, the cabin battery was always slowly draining until it and the starter battery evened out. I checked the diodes on the isolator under the hood and it was definitely bad, so I replaced it and that solved the 'draining while parked' issue.

Next was the fact that while plugged into shore power, the 12v system never seemed to charge. As a matter of fact, when I plugged into shore power, I could see the voltage in the 12v system jump from about 12.4 volts briefly to above 13, but within seconds, drop back down to the resting voltage of the battery. Why did it take me two years to realize this?

Anyway, I fixed this by getting a nice new 120v to 12v converter - one that put out 55 amps rather than the original 32 and used modern electronics to charge the cabin battery. I bought the 55 amp model from here: Upgrade Kits for Magnetek/Parallax

Pulling out the old converter and plugging in the new one was pretty straight forward, but was made more difficult due to the tight fit of the cabinet it's held in. The most time was spent labeling the 12v wires so I'd put them back in the right order! PM me if you are thinking of doing this and need any help.

Wow, what a difference! Now, on shore power, I can flip the cabin's power button and see exactly what you'd expect! The voltage at the battery jumps up to a perfect 13.4 volts to charge - and it's also smart enough to jump up higher if necessary, or lower for a small amperage trickle charge. And, get this, all of the 12 volt appliances now have a bit more gusto! The lights are a bit brighter, the fans are a bit faster, and nothing dims or slows down when you turn on something else - the new 55 amp service (when plugged into shore power) is fantastic and totally apparent!

At this point, I don't think there's a single wall, wire, hose, pipe, window, curtain or light I haven't either replaced or fixed on this old lady - but with only 30,000 miles on it, it's worth it. She drives like new and the kids and I love camping in it! Hope this post helps someone out there!

[peppster66]

that's great, glad you were able to fix it, Im having similar issues with my 97 dodge roadtrek, so I will look into these fixes, thank you very much,,,,

[VTPete]

Let me know if you want any advice - and for the record, the actual charging voltage is 13.2 for float, 13.7 for regular and 14.4 for rapid charge. I like the new unit.

[booster]

Originally Posted by VTPete

Let me know if you want any advice - and for the record, the actual charging voltage is 13.2 for float, 13.7 for regular and 14.4 for rapid charge. I like the new unit.

Did you install a battery monitor while you were at it? Very difficult to know if you are getting over or under charged without it. The PD chargers run a fixed timer absorption cycle, so you can get either over or under with them, based on depth of discharge and bank bank size and type.

[Kr4ftw3rk]

As Booster asked,

"Did you install a battery monitor while you were at it?"

I just upgraded my old Magnetek to a PD4645VL converter in my 95 Roadtrek and was wondering about a monitoring system.

Like to know if you're thinking the same thing.

Also, thnx for the heads-up on the isolator. Mine is the original Hehr-Powerline and tomorrow will be taking a voltmeter to it. It doesn't look like a difficult component to replace if it's bad.

[VTPete]

Actually, I made one that allows me to monitor the battery - and has a low and high voltage alarm on it. I made it from the following off-the-shelf components:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
(It was only $8 when I bought it.)
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

After setting the proper voltages to trigger the alarm, I cut a hole in the box, added the switch and wired it with a 1 amp fuse directly to the battery. And, I don't remember what voltages I chose for the alarm, but it was around 12v for low and 14.7 for high. It draws almost nothing and I mounted it near the power converter so that I can glance through the window to see the voltage at the battery. This way I could finally see what was happening when it was supposed to be charging. The switch I added to the box allows me to shut it off for longer storage so there's no vampire drain on the battery.

As for the isolator, wiring it up is simple, but installing it was a hassle due to the location and getting to it. In the end, I was able to use two of the existing holes in the van's body, but had to drill two new ones as the new isolator's mount wasn't the same as the original. I made sure to silicon up the new holes!

The isolator I installed was this one from Amazon: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Man, it sure is nice being able to go back and search through my orders on Amazon!

[booster]

Originally Posted by VTPete

Actually, I made one that allows me to monitor the battery - and has a low and high voltage alarm on it. I made it from the following off-the-shelf components:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
(It was only $8 when I bought it.)
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

After setting the proper voltages to trigger the alarm, I cut a hole in the box, added the switch and wired it with a 1 amp fuse directly to the battery. And, I don't remember what voltages I chose for the alarm, but it was around 12v for low and 14.7 for high. It draws almost nothing and I mounted it near the power converter so that I can glance through the window to see the voltage at the battery. This way I could finally see what was happening when it was supposed to be charging. The switch I added to the box allows me to shut it off for longer storage so there's no vampire drain on the battery.

As for the isolator, wiring it up is simple, but installing it was a hassle due to the location and getting to it. In the end, I was able to use two of the existing holes in the van's body, but had to drill two new ones as the new isolator's mount wasn't the same as the original. I made sure to silicon up the new holes!

The isolator I installed was this one from Amazon: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Man, it sure is nice being able to go back and search through my orders on Amazon!

Be aware that a voltage cutoff will not give you any kind of accuracy on the fully charged end if you have lead acid batteries, either wet cells or AGM.


To get lead acid batteries full, they need to be held at full absorption (boost to PD) for many hours before the batteries get full. What amount full they will be is kind of based on battery bank size and charger size. Small bank with big charger will be less full when the absorption voltage is reached. Big bank with small charger will be more full at the transition. In general it would be somewhere between 70% and 85% full for most systems.



Here is a charge profile matched up with a state of charge diagram. Note how much time is left once the voltage levels out and how far the state of charge is from 100%. This is single cell stuff, so need to mutliply to get normal battery voltages.

[Bud]

"Actually, I made one that allows me to monitor the battery - and has a low and high voltage alarm on it."

I don't understand. You have battery voltage monitoring with alarms for high and low with a switch. Does anything happen without You? Does this simply alert you so that you can stop charging or stop using the batteries?

Bud

[VTPete]

Hi Bud,
Yes, it's just a monitor that requires a human to interact with it. I created it to keep an eye on the charging voltage as well as the running voltage of the battery.
The charger itself is supposed to handle the over-charge. As for draining, the little box just lets out an ear piercing scream when the voltage gets too low.

To be clear, I added it mostly as a diagnostic tool as well as a warning that would help me wake up in the middle of the night and (for example) turn off the fan if the voltage dropped too low on the battery. As for the diagnostic side, I just wanted something better than the 4 LEDs on the control panel.

-Pete

[booster]

Originally Posted by Bud

"Actually, I made one that allows me to monitor the battery - and has a low and high voltage alarm on it."

I don't understand. You have battery voltage monitoring with alarms for high and low with a switch. Does anything happen without You? Does this simply alert you so that you can stop charging or stop using the batteries?

Bud

It is mentioned that it is used as a visible check of if things are charging or not, so that would probably also be possible to see voltage while discharging also.



As has been discussed so many times, voltage (especially when load is on) is a very poor way to monitor state of charge. Bud does it by experience and with a lot of past data collecting and testing so much closer than most.



At the very important 100% full during charging point, voltage really isn't able to identify that point even on a rested and unloaded battery as the voltage hardly changes for maybe the last 3-5% of charge. Getting batteries consistently full without overcharging is not simple thing, and as AFAIK, measuring amps is about the only way to do it accurately and consistently.

[booster]

Originally Posted by VTPete

Hi Bud,
Yes, it's just a monitor that requires a human to interact with it. I created it to keep an eye on the charging voltage as well as the running voltage of the battery.
The charger itself is supposed to handle the over-charge. As for draining, the little box just lets out an ear piercing scream when the voltage gets too low.

To be clear, I added it mostly as a diagnostic tool as well as a warning that would help me wake up in the middle of the night and (for example) turn off the fan if the voltage dropped too low on the battery. As for the diagnostic side, I just wanted something better than the 4 LEDs on the control panel.

-Pete

Here is the PD charge profile with a Charge Wizard model.






As you can see, the charger runs strictly on timers so it has no idea of what the state of charge is or if it is over or under charging.


PD chargers have a huge advantage over other chargers in that the charge states can be manually run from the Charge Wizard by the operator. By watching a monitor for a "charge complete" light or even just an ammeter to look at amps to the battery, the charging can be controlled by the operator and be very accurate.



There are only a very few chargers that will monitor the charging conditions and automatically do that for you.

[booster]

Found a bit better graph showing a typical lead acid charger profile and state of charge during the charging process. This one show voltages typical of the 12 stuff RVs normally use.





Yes, those times are in hours, and that is how long it takes many times. Most chargers use much less time that than this at absorption voltage so can chronically undercharge. The Imin they show is what you would be monitoring and making sure you go to float at that point.

[Bud]

Thank you gentlemen.

Pete, this is what kind of jumped out at me, had not dawned on me:

"To be clear, I added it mostly as a diagnostic tool as well as a warning that would help me wake up in the middle of the night and (for example) turn off the fan if the voltage dropped too low on the battery."

So I got to thinking, could I have used that application over the last 3 years? Since for the first time in my life, I was going to maintain batteries appropriately. The battery under the back seat of my Beetle never hardly saw any water, much less any of the distilled stuff. Now wow, 2 new Walmart batteries, distilled water, battery tender when not in use. But still a dumb charger, inappropriate cabling, and driving off with full charge for 8 hours (probable overcharging).

When going to bed I might lower the thermostat on the fantastic fan and see 11.8 volts when fan kicks on high, which is not problem. Lower the fan to low shortly after and asleep. But if it 30-40 degrees out, poor/no insulation in a 05/04 190P the furnace could very well be a problem. Now what? I start the van's engine which when cold idles at just about the right rpm, 1000. Then a short adjustable shower curtain rod to maintain the rpm after the engine warms up a bit. I'll add 10-25 amps. I've only needed to do this a few times.

I think maybe I'll add this feature? Thanks Pete.

Bud