100W solar panel with Victron Shunt

[raj]

Hi all!
I have a Micro Minnie trailer and I have 2 12v deep cycle batteries connected. Previously, I purchased a 100W Solar panel along with controller from Costco. It seemed to work well, charging the batteries during the day and giving us enough power to last through the night.

Recently, I added Victron Shunt which has builtin bluetooth. It works well and gives great information about power usage and battery charge state.

On my last trip (first one using the solar panel with the shunt also), I noticed something very strange. I'm including a picture of the voltage reading from the shunt during 2 days. We started with a full charge from campground hookup and ended charging back to full at home. You can see, in the picture, how the solar charged during the day, but once the sun went down, the voltage level went back to where it would have been without any charging at all!

As is supposed to be the case, I have the shunt connected between the negative terminal of the battery pair and the negative wire from everything in the trailer, including the solar panel charge controller.

What am I missing?

[Marine359]

Hi Raj,
Process of elimination.
Solar panels are dumb. They just send power down the wire. Can’t be that.
Victron shunt is bulletproof. Seem you installed it properly, so can’t be that.
That leaves the solar charge controller.
Is it a brand name good product, or did you get a pig in the poke from Costco?
Is it mppt or pwm?
If the controller doesn’t have Bluetooth, put a clamp ammeter or multimeter around the positive output wire between controller and battery. The reading should be 6 amps for a 100w panel in good sun. If you’re getting something less, you could have a skunky charge controller.

If the. Victron indicates your battery received charging during the day, and you peeked at the battery voltage, the battery voltage should not drop precipitously on your way home, unless you’ve got a bunch of dc loads runn8ng (like a compressor fridge). Additionally, your 7-pin should be sending 4-8 amps to the battery while you’re driving. So, if voltage was good when you started driving and bad when you got home, that would indicate to me a faulty battery bank. Have you tested your batteries?

[creativepart]

Are those FLA deep cycle batteries? That voltage looks high if they are. Also what’s the time frame for that chart? 4.05 - 16.05 - 4.05? That’s what I see, but don’t know what that means exactly.

A PWM charger pulses like that… it the P in PWM.

Basically, I’m at loss. My best guess is also bad battery(s).

[raj]

Yes, these are FLA deep cycle batteries. I would tend to think they're ok, since they held sufficient charge to last 3 days, which is about what they have always done in the past. The controller is the Coleman 8.5 amp one you see all over the place. I've had it for quite a few years.

I don't have a clamp multimeter, but I do have a probe one. This morning, I connected up the new solar panel, placed it in as much sun as I have near the trailer (which isn't a lot, but should be sufficient for some charging). I then disconnected the charge controller positive wire from the batteries and inserted my multimeter between the controller output and the batteries. My shunt showed a decrease is draw down by about .5 amps, which agrees with what the multimeter said at 0.55 amps. Even with the panel not pointed directly at the sun, I would expect the current to be higher than 0.55 amps. I'm beginning to suspect the controller. Unfortunately, since I don't have another one to switch in, I'll just have to purchase one.

[Marine359]

Good troubleshooting Raj.
Which make/model controller came with the package you got from Costco?
The Coleman controller is a cheapo pwm. You’ll be better off to replace it with a quality mppt controller. The Victron Smart 100/30. Has enough capacity to allow you to add a lot more panels in the future. If you don’t plan adding more panels, the Victron smart 75/15 will get the job done at half the price. And you can see what it’s doing on the Victron app. It’s mppt, so will make the maximum power possible (maximum power point) from your panel(s).

If you’re happy with your battery performance, then ok, just try to max out the array.

[raj]

Ok, here's an update. I had already purchased a new solar panel and have now purchased a new solar controller (a MPPT model). I purchased a hydrometer, charged the batteries on shore power over night, to be fully charged, then disconnected the power and tested with my hydrometer. Both batteries test about the same. In the picture, you'll see that the test clearly shows that the battery is bad and should be replaced. So, it looks as though a new solar panel wasn't really necessary and the controller may also be working fine (but it's a cheap Coleman anyway and a new MPPT controller will certainly work better). It looks as if the real culprit is the 2 year old deep cycle batteries from Walmart. I admit they only cost ~$85 each.

So, the next question is what would be a good deep cycle battery to get? Something around 100Ah and Group 24 size would be good. I don't want to spend a lot and I don't really want to go with Li right now. Any suggestions?

Maybe a desulphator is worth a try before spending a lot on new batteries?

[Marine359]

The price of LiFePo4 has collapsed in the past three months. Lithium now cost almost the same as lead acid per useable watt hour. If you go with deep cycle again, you’ll spend $170 for two deep 100ah marine deep cycles from which you’ll be able to use 100ah of that consistently, or 150ah of that in a pinch occasionally without damaging the batteries. And eventually, you’ll have to replace them again, and again, and again. Today, you can buy a 100ah LiFePo4 for about $225, with a full useable 100ah, and it will last longer than you’ll own the rv. If you’re on a budget right now, you don’t have to buy anything else. Just drop it in and charge it with your existing converter/charger and your solar.

Check your converter/charger. Recent models of Micro Minnie’s have programmable or self-detecting chargers. If you’re not sure, you can check by partially disassembling the breaker panel, or call Winnebago customer service, give them your VIN#, and they can look up your build and tell you what model it has.

These days, there is NO good reason not to buy LiFePo4 when doing a battery replacement. Smart move is to look for a low price on a pair of 100ah LiFePo4. I’m thinking a saw a pair on Amazon for around $400 for the both of them. Having a full 200ah of consistent 12v power will dramatically change your camping experience.

[raj]

Thanks, I see the types of prices you're talking about and it's, indeed, temping. Looking at my trailer, I see it has the somewhat usual "WFCO WF-8900" power distribution center. I'm going to look up information online to see if it can handle LiFePo4.

Thanks for the tip!

[raj]

It looks as though I have a WFCO WF-8955PEC unit and apparently I can easily convert it to LiFePO4 compatibility by installing the "#PD4655V", which replaces the DC converter and control unit for better LiFePo4 compatibility, for around $260 or so. It also looks as if not doing this will mostly like not hurt the LiFePo4 batteries much, it mostly just means that they take a bit longer to charge completely. If I'm charging the batteries from solar most of the time, I would be using the solar controller instead of the trailer unit anyway.

That being the case, I'm thinking of going LiFePo4 and making the switch to the trailer unit a little later, thus helping to spread out the cost.

Opinions?

[Marine359]

Good move.
You may decide later that you want to invest some bucks in an inverter, in which case, it become easy and not much more expensive to opt for a hybrid inverter/charger, which can charge LiFePo4 exceptionally fast. But, by just using what you’ve got, you’ll enjoy most of the LiFePo4 benefit and keep your options open for the future.

[BobC]

There are some good, inexpensive LiFePO4 batteries out there and some pretty bad ones so buyer beware. Will Prowse is a Youtuber who regularly reviews batteries, complete with teardowns that often expose poor construction. Here are a couple of links:

Videos: https://www.youtube.com/@WillProwse

Recommendations: https://www.mobile-solarpower.com/li...batteries.html

Note that the prices shown may not be current.

[raj]

Thanks, I'll check it out!

[raj]

Ok, I sprung for 2 LiFePO4 batteries at $200 each, plus the new AC - DC charge unit for the trailer $280, so I should now be all changed over and taken care of. I’ll report back once it’s all installed and tested out. Thanks, everyone, for the help!

[Marine359]

Well planned Raj,
Post pictures after installing.
Consult photos from albums of Fred2106, Tinglett, and myself if you need installation ideas.

[BobC]

Originally Posted by raj

Ok, I sprung for 2 LiFePO4 batteries at $200 each, plus the new AC - DC charge unit for the trailer $280, so I should now be all changed over and taken care of. I’ll report back once it’s all installed and tested out. Thanks, everyone, for the help!

If your batteries don't have low temperature charging protection, you'll need to take extra care and not charge if the ambient temperature in the battery compartment is 32 degrees F or below.

[raj]

Really? I wasn’t aware of that. I wonder if my new charge controller takes care of that. Probably not, but I’m not aware of a device to handle this.

(Looking back at the batteries I ordered, I see they specifically say, “low temperature protection”.)

[BobC]

Originally Posted by raj

Really? I wasn’t aware of that. I wonder if my new charge controller takes care of that. Probably not, but I’m not aware of a device to handle this.

(Looking back at the batteries I ordered, I see they specifically say, “low temperature protection”.)

Your charge controller most likely won't. It's good that your batteries do. What batteries did you order? You lucked out since many low cost batteries are missing this protection.

Even with protection, I'd be wary, especially if you live where it's particularly cold. If you're having a particularly cold snap and your batteries are charging 24/7 via solar or charger, I'd disconnect them. They'll be fine disconnected with no load for a few months if they're fully charged. This means disconnecting the Neg battery cable from the batteries, not just using your RVs battery disconnect switch, which doesn't disconnect parasitic loads such as your propane alarm, etc.

For others reading this, the video I highlighted in post #11 shows the lack of low temp protection in some of the teardowns. This is one of the downsides of shopping solely by price without fully investigating the details and not educating yourself about LiFePO4 batteries before buying.

[raj]

I'm east of San Diego, CA, so we basically never get below freezing, however we sometimes visit places which do. Instead of disconnecting all power from the trailer completely, I wonder about maybe inserting a switch on the AC-DC converter wire which would charge the batteries? This way, the batteries wouldn't charge but would still feed electricity to everything else in the trailer? I'll certainly see tomorrow whether or not this even makes sense, once my new AC-DC converter/charger unit arrives for the trailer power center.

By the way, I went to Amazon, looked for LiFePo4 batteries which are "Class 24", so they fit where my current deep cycle marine batteries are, then sorted by average customer reviews. The one at the very top was the one from WattCycle (about whom I've read some other good reviews, saying they're an up-and-coming Li battery company, making good stuff at a good price). Here's the link:

https://www.amazon.com/Wattcycle-LiF...904010ad0&th=1

[Marine359]

If you disconnect the converter charger either by installing a switch or by flipping off its breaker, you will not have any 12v dc power going to anything in the coach. The easiest way to stop charging the batteries with the converter while hooked up to shore power is to shut off the battery disconnect. You will then still have both ac and dc power going to the coach from the converter, but not to the battery. I believe this is true, but not really sure, since I re-wired my MM when I installed an inverter/charger. Try it first to see if the charging circuit becomes disabled. If that doesn’t work, it’s a simple matter to install a second disconnect switch ($35) between the battery and the dc bus (which is operated by your existing disconnect switch. By doing that, you don’t disturb the circuitry wiring of the primary disconnect switch which is connected to loads, and you will be able to isolate/disconnect the battery from all circuits, including phantom loads.

[BobC]

I took a look at the info on your battery and although they do state there's "low temperature protection", the text speaks to operating at low temperatures, not low temperature charging:

"Low Temperature Protection: Designed to withstand extreme temperatures, our battery can operate in conditions as low as -4℉ (-20℃) and as high as 158℉ (70℃). It adapts seamlessly to various climate environments."

This is not the same as low temperature charging protection. Note the difference between the above and LiTime's description of their $300 battery:

"[Low-temp Charging Protections & Force charge] The 12V 100Ah smart LiFePO4 battery have built-in low temperature charging protection that will automatically cut the battery off from charging when the cell temperature is lower than 32℉. Preventing the battery cells being damaged from charging under the freezing point. When needing to charge the battery under low temp charging protection, by pushing the button it will disable the protection and allow emergency charging under freezing point."

When disconnecting your batteries from your onboard charger as recommended by Marine 359, you'll need to make sure your solar controller and tow vehicle charging sources are also disconnected.

I don't have first hand knowledge of the BatteryProtect device, but here's a post from the Grand Design RV forum that discusses this very issue along with a $40 device (65A) called a BatteryProtect from Victron:

https://www.mygrandrv.com/forum/show...ther-Charging?

https://www.amazon.com/Victron-Energ...61&sr=8-3&th=1