Popster Power!

Here is the saga of my mom’s 4 Wheel Camper which sits on a 2002ish Chevy Silverado 1500. It’s an old model that has seen a LOT of miles and use.

Popster on the move

My mother had let the Popster sit for a couple of years after my dad’s passing. My dad used to leave it pulled in all the time to keep the lithium batteries topped off. My mother had not. Thinking she wanted to get out again, she tried plugging it into shore power and charging the batteries. While they would charge, they also seemed to discharge quicker than she remembered. She assumed the batteries were old and worn out.

The “fun” part is that the batteries sit in the truck bed, just ahead of the wheel wells and under the camper. You can access the batteries through tiny openings inside the camper, but you can’t take them out.

Driver side battery bank

There are 12 lithium batteries total for 12v, 6 per side; 4 groups in series of 3 cells in parallel. My mom had my dad’s notes on when he set up the system where he had 3 diagrams. The first had a big X through it. The second had some arrows indicating that he swapped some things around. The third has all the monitoring wires added for checking the voltage at each bank. There was a 4th page with colors to indicate the positive and negative poles of each cell, but there were no lines to represent how they were tied together. Obviously incomplete.

Passenger side battery bank

Mom had found a repairman that sounded ideal. He was a retired Seimens Field Engineer who did on-site RV repairs. My dad had been a GE Field Engineer, so she assumed that meant good problem solving skills. He came out, unbolted the camper from the truck bed and jacked the camper up to expose the batteries. After testing the batteries, he deemed them ok. In doing so, he disconnected the cells and tested them individually. Mom had given his diagram #3, as it was the most recent, complete diagram, to reassemble it.

Put back together, the system didn’t seem to function. The repairman claimed it wasn’t hooked up correctly, but rather than fix it, he waited for my mom to run an errand and then dropped the camper back down and threw some random bolts to hold it onto the bed of the truck and ran off. Never to return.

In hindsight, it’s a good thing he never sent her a bill.

So, my mom drives the Popster out to my house. Along the way, she drove up the Moki Dugway and then the Burr Trail, taking the scenic way around. Although both roads are rated challenging, she didn’t think they were hard at all. As someone not super comfortable with heights, she found it much easier to be behind the wheel as opposed to being a passenger.

My turn to figure this mess out. I break out the voltmeter and look it over.

Easy Peasy!

⁣Uh, sure. This looks fun. First thing, I measure at the blue connector that separates the battery bank from the 12v system of the camper: 0.47v. So, not great. Then I measure each 3 cell bank of batteries. These measure 3v across each group of 3 cells. Ok. And then 6v across each bank of 2 groups. Um…what?

So, remembering college … who am I kidding, I googled this shit….voltage adds in series. So 4 groups of 3 cells (each 3 cell groups is 3v) should equal 12 v. But I have zero, or almost zero.

Time to measure from ground. First group, 3v. Second group 6v. Third group 3v. Wait…not 9v? Then I notice the polarity. Yup…it’s wrong.

I pull out my dad’s notes and it is wired just like the drawing #3. Which makes no sense electrically. So, I look over all his notes. Drawing #1 is crossed out and also doesn’t make sense electrically. Drawing #2 makes sense, but is a little messy on the order, with wires all over the place. Then I notice that on the passenger bank he has a double ended arrow indicating that he swapped the front and rear banks. Now THAT makes sense electrically.

Looking at staying #3, I realize that its main purpose is to document his cell group measurement wiring, which was designed to check the voltage of each group. Looking at drawing #4, it matches the swapped drawing #2 and how I think the batteries should be wired ONCE I realized that green is ground and red is positive. As a mechanical engineer, I assumed red was negative and green positive. But to electrical engineers, green is ground.

One other clue that things weren’t wired correctly was that the big wire from the trucks alternator (through an isolator) was attached to the battery bank on the rail that would have produced 9v. Again, it made no sense to connect it there.

That Seimens Field Engineer was an idiot.

So, now I had a plan. I moved wires and jumpers around. I didn’t worry about the measuring leads as they weren’t currently hooked up to anything. Once it was all bolted together (and not once did I fry myself!), I put the voltmeter on the blue connector.

Drum roll, please……..


BOOM! I am stoked! The fact that the battery cells held over 3v each for a long time while hooked up half backwards amazed me. I mean, shouldn’t there have been sparks? A drain of potential? Sometimes, electrical wiring is just voodoo.

I happily bolt the rest of the system back up, thinking I’m almost done. With everything together, I plug the blue connector together, mating lithium battery bank to the RV systems. Lights come on. The refrigerator starts to hum. Kickass!

I leave it hooked up that way overnight. The battery bank drains down quite a bit, but I did have all the lights on, the fridge trying to cool down from ambient temp and I charged my laptop to stress the system.

Looking over some internet info, it looks like the batteries should charge to 14+v, so starting at 13.3v wasn’t a good test of the system. I go around and plug the camper into shore power and check the voltage. No change. Huh. The converter doesn’t even appear to hum, which is a mechanical engineers clue that something electrical is working.

Disconnecting the converter, I verify that it has 120vac coming into it but 0vdc coming out the other end. Not very good. Time to do some research for troubleshooting. To the internet.

The first thing I notice is that there should be 2 blade fuses next to the 12vdc connections. I glance over and don’t see any. It’s on the far right and difficult to see up against the side of the camper. But nope. Definitely no fuses.

Stupid Silver Box

It takes 35amp blade fuses. The best I can tell, they have 30 or 40a fuses, but no 35a. I figure 30a are fine. They will just pop sooner. I find a couole laying around and try to install them.

And they fall right out. Using a flashlight and a mirror, I can see that the fuse holding sockets are opened up. I try to tighten them, but can’t get a good angle, so I figure screw it and completely take the converter out. It’s not hard, yet not easy either.

Having the converter out, it’s obvious that a normal bladed fuse won’t work in its current state. But it’s easy enough to curl the two sides down until they hold the blade tightly. I insert two fuses and reinstall it all again.

Well shit. Same problem of no voltage out the DC side. Playing with the fuses, particularly the top one, I can get the converter fan to come on temporarily and a voltage spike to 14v even more temporarily. Figuring it is a fuse holder issue, I remove it again.

Take it to the bench and drill out 14 rivets including the ones right next to the “No serviceable parts inside. Do NOT open the case!” warning label. With the cover off and my multimeter measuring continuity, I can show connection some times and not others (mostly) by wiggling the fuse. I heat up the soldering iron and heat the fuse terminals to apply more solder. After cooling, the soldering seems to have made better continuity between the two fuse sides. So, I reinstall it.

Same damned problem. Now, I can get any power out of the thing. I’m starting to thing that the converter was starting to go bad when my mom first tried using it. Now, it definitely is. Not output power at all.

Doing more research, they make one that looks identical, but is made more lithium batteries. Time to order new parts. Unfortunately, mom needs to be back home before the part would arrive, so she will have to have it installed there.

On a good note, however, is that the truck will charge the batteries while it is being driven. There is also the issue of one of the three solar panels not being connected on the roof, or so my mom tells me. More projects for the future!

Oh, and on the camper to truck bed mounting bolts… Of the four corners: one was tight; two were loose but not about to fall out; and the fourth…well, it was twice as long as it should have been and could never have been tightened. None had lock washers. Two were missing the fender washers. Thanks Seimens Field Engineer, you dick.

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