Too much battery? (1 Viewer)

[RandyDaytona]

Is there such a thing? Disclaimer: I’m a fairly non-tech-savvy person regarding batteries. I’m looking at the EcoFlow batteries and similar and seeing how everyone uses them. I’m thinking I may not need that much power.

I have recently set up my fridge in the back of my 200. It previously lived in my work truck and was plugged into a socket that was always on, and since I drove it every day, it was a non-issue.

But now, for the first time, I’m considering adding a battery to the mix. I figured I would plug my fridge into a small battery, which would then be plugged into the DC socket in the LC cargo area and would charge when the vehicle runs. When I stop for the night, the battery would run the fridge until morning, soon after which I’d hit the road again.

Is there a better-sized (or better suited) battery for this kind of application? Maybe one that takes up less space? Sorry if this seems like an ignorant question!

Edited to add: I would not be powering anything else. Just the fridge, which is admittedly probably older than most mud members , if that has any bearing on power requirements.

 

[Mike6158]

Nope. All you need to do is make sure the voltage is the same. Battery A/hr ratings are just that, a rating for how many amps per hour you can pull out of the battery before pulling the voltage too low. Renogy.com is a more wordy

Amp-hours, or Ah for short, are a unit of measure for a battery's energy capacity. This rating tells us how much current a battery can provide at a specific rate for a certain period. So, for example, if you have a fully-charged 5-Ah battery, it can provide five amps of current for one hour.

I have a LiFePO4 battery that I carry with me that is 70Ah. I can run 7 hours at 10A (but I wouldn't) and longer if I connect it to a solar panel.

 

[sdnative]

If all you are powering is a fridge overnight, and you are able to recharge the battery fully every day (whether driving with DC/DC or stationary with solar), you won't need much capacity. I would think 40Ah/500Wh of usable capacity (probably even less than that) should be more than sufficient. I am assuming you are considering LiFePO4 batteries.

Fridge power consumption varies, but my insulated ARB consumes less than 1 Ah / hr when full and contents have reached temperature equilibrium.

 

[e9999]

If your current setup of one battery works for you, there may not be a need to do anything different. Now, is it a good approach? I don't think so, mostly because I would not want to take a chance on the only battery getting discharged and being stranded. But if yours won't get discharged too much, then it works. What is your rationale for going the new way?

As to adding another battery, there are some complications, such as mixing different types like lead acid and lithium, isolation, charging schemes, etc, but this a bit more complicated than looking at just basic capacity issues. Otherwise, then, just from an energy point of view based on your scenario, adding another battery is equivalent to having a bigger one under the hood. So, figure out what is the longer period you expect to experience without charging, calculate fridge use for that period, give it a bit of safety margin, and you'll know how to size it, given how much you want to discharge it. (If you don't, there are plenty of info on that out there that is worth getting familiar with.)

As to the type, if it were me, I'd start by looking at the newer small size 100Ah LiFeP batteries. Pricier than lead AGM probably but much lighter and way longer life expectancy so I suspect it may be a toss up or -likelier I think- cheaper long term. But you should not just connect Lithium and lead directly. You would not want to put a flooded lead acid in the back, either, though, cuz of fumes, spilling etc, but having an AGM in the back would make things much simpler than lithium in terms of connections.

Don't just put any battery in the back, connect it in parallel and call it a day, there are issues like I mentioned above that have to be addressed. And make sure it is held in place properly cuz a loose heavy battery may barrel through the seats and through you if you ever have a serious frontal hit. Or would become a blender if you were to roll over.

Also, rereading your OP, and to be clear, keep in mind that with the setup you described, you would not have just the back battery running the fridge, it would always be both.

 

[Mike6158]

This is an example of a good way to protect your ability to start. There are quite a few out there.

 

[LandLocked93]

Is there such a thing?

No, actually.
The key is charge/re-charge abiltity.

I have recently set up my fridge in the back of my 200.

So...in terms of current draw, what does the fridge you have draw? (with voltage drop included)
And I'm talking max current draw. (startup mainly)
Design the wiring to that.
This ensures all other current draw amounts are covered.

But now, for the first time, I’m considering adding a battery to the mix. I figured I would plug my fridge into a small battery, which would then be plugged into the DC socket in the LC cargo area and would charge when the vehicle runs. When I stop for the night, the battery would run the fridge until morning, soon after which I’d hit the road again.

Ok. But ensure that the "small battery" has the capacity to run your fridge over the night hours.
And that capability is calculated relative to the max and min current draw of your fridge.

Is there a better-sized (or better suited) battery for this kind of application?

Beyond the capacity calculations, re-charging said battery is the next concern.
There are probably only 2 ways to do this, depending on batt chemistry and charge-wire length.

 

[RandyDaytona]

Wow - awesome information guys!

I actually carry around a commercial-grade jump pack. Bigger than necessary and a long story, but I’m not too worried about being stranded.

The reason for the change is that my old govt truck had a DC plug that was always on. And even if I didn’t drive it the next couple of days, the fridge would keep going and the truck would *usually* start anyway. In my LC, however, the rear/cargo DC plug is not always on, so when I stop, it stops. And I’d like it to keep chilling. I know there are ways to change it so it’s always in, but I’d prefer not to go that route.

I’ll have to make sure of the power draw when I get back home, but I believe I read somewhere that it was something like 3.5 amps. It’s a Norcold Tek II. I believe it’s from the 1980’s. Maybe earlier. Got in on Craigslist around 2015 from a guy who used it solely for his annual Lake Michigan fishing trip and it was in mint condition.

Thanks everyone!

 

[LandLocked93]

Wow - awesome information guys!

I actually carry around a commercial-grade jump pack. Bigger than necessary and a long story, but I’m not too worried about being stranded.

The reason for the change is that my old govt truck had a DC plug that was always on. And even if I didn’t drive it the next couple of days, the fridge would keep going and the truck would *usually* start anyway. In my LC, however, the rear/cargo DC plug is not always on, so when I stop, it stops. And I’d like it to keep chilling. I know there are ways to change it so it’s always in, but I’d prefer not to go that route.

I’ll have to make sure of the power draw when I get back home, but I believe I read somewhere that it was something like 3.5 amps. It’s a Norcold Tek II. I believe it’s from the 1980’s. Maybe earlier. Got in on Craigslist around 2015 from a guy who used it solely for his annual Lake Michigan fishing trip and it was in mint condition.

Thanks everyone!

The "always on" DC outlet in the gov't truck is just a wiring thing.
Your 200 that switches off the DC outlet to which the fridge is connected is also just a wiring thing.

Recommend a DC to DC charger that contains charge profiles (Renogy, RedArc) or battery bank (Jackery, Zero, etc) to keep the small battery topped off while you drive. A direct wire from small batt to DC outlet can work but it's neither efficient nor fully effective. And could be dangerous in some situations.

 

[ntsqd]

Since the Power Port goes dead with the key off that's a pretty good battery separation method.

I would suggest looking into the lithium option too. It hits all of your bullet points. The charging of it is really the only question. An issue with any lead-acid battery is that you can only really use about 1/2 of it's rated capacity. Drawing more than that is good way to drastically shorten the life-span of the battery and even drawing down to a 50% State of Charge is not a great idea. So a 100 AHr rated lead-Acid battery is usefully really only about a 40 AHr battery. I'm reading that lithium batteries can be drawn dead flat, but I expect that's over exuberant marketing and the reality is somewhere in the 80%-90% range if you want the longest battery life.

Truth is that you could probably run the fridge off of that jump-starter that you carry. Not that I would, but that you can. If you can figure out a way to log how many amps it uses in a typical day I suspect that you'll find that such a battery won't need to be very big (physically or AHr capacity) to run the fridge w/o charging for a couple of days.

 

[AndrewHadji]

i have 400AH of 12 v in the troopy, it is too much battery for the manager 30.... limited to 30 amps recharge rate, it takes me 8-10 hours from 10 % abouts. @LandLocked93 has it right, you can have a huge bank, but if you cant recharge them fast enough, or at least fast enough to replenish demand.... yea... i really enjoy not having relying on propane for cooking or heat or hot water. a typical day of stay in a spot camping takes me down to 85% abouts.

 

[RandyDaytona]

Thanks guys.

I ended up ordering an EcoFlow Delta2, which arrived this week. I’m just starting to set it up (though everything is pretty well “set up” already, right out of the box).

Thanks again!