Framework for Inexpensive Off Grid Aux Electrical

luthj

Adventurer
Hey folks.

A friend of mine asked for some advice on a basic electrical setup for a medium sized off-grid type vehicle. The major concerns were high value, reliable components, and Simple configuration. The components listed below have either been used/installed by myself, or have good history.

Attached PDF, and the table below have the core components for an electrical system, that if installed and sized properly, will provide good service at a reasonable cost. At least in my opinion.

Due to issues with inserting a table, I will insert a photo below. For the web links, open the PDF file attached to this post.

Electrical Components.png

Some more details:
  • This system is based around a ~220AH 12v lead acid bank. The battery bank could be doubled for 440AH (or tripled).

  • Wire and fuse sizing will need to be chosen by the installer. I have included a hammer crimper and insulated ratcheting crimper. The hammer crimper is not a professional tool, but with a concrete slab, and a sledgehammer, acceptable crimps on larger lugs can be accomplished. Not that 3x crimps per lug is needed.

  • The Victron solar charger should be set to 14.8V absorb and 13.5V float. Use of the temperature sensor option is suggested. Absorb timer should be at least 4 hours.

  • The ANL fuse should be sized according to the main wiring size, and the expected loads. 50A is acceptable for many installs, but up to 200A is possible for high load situations.

  • I chose an inexpensive charging relay (Stinger). However for installs that have short low resistance alternator charging runs, a Blue Sea 120A ACR, or a heavier relay/solenoid may be called for.

  • The solar panels are cheaper poly type. For those who need light weight or more compact, the mono grape solar panels are a good choice. They produce more power per square foot, and weight less per watt. They are more expensive though. The Victron controller will handle 200W of panels without de-rate, 300 or 400w of flat mounted panels would be acceptable. Just note that you will loose a small amount of peak solar power due to the controllers output current limit.

  • The Victron Battery monitor and Solar controller both have bluetooth control options available.

So the big question; What can this setup run?

Under mostly sunny conditions in the lower 48, this should run a 65liter DC fridge. It will handle LED lights, phone charging etc for most folks. Running a laptop for a few hours a day, etc. Obviously each person needs to do their own math to figure out the details.
 

Attachments

dwh

Tail-End Charlie
Pretty sure that model Victron doesn't have an external temp sensor option; internal sensor only.


Also the absorb time *limit* is preset to a multiple of the bulk stage, like..

(absorb max time) = (bulk time * X)
where X is defined by the battery voltage at first light

The highest value for X is 1. So say battery voltage at first light is >12v, then X is set to one. If bulk then takes say, 5 hours, then absorb is set to 5 hours *max*. The preset max time limit at (X=1) is 6 hours. Which is plenty because if bulk takes more than 6 hours and absorb is set to 6 hours max - the sun will go down before the absorb stage ends.

I haven't messed with the settings on my 100/30 as one of the presets on the rotary switch exactly matches my batteries' specs. And I don't use the bluetooth dongle because I use the Victron meter instead.

So I could be wrong, but I think that setting the absorb timer to say 4 hours does not force the absorb to continue for 4 hours, it just limits it to 4 hours *max* - which might not be enough if the battery was low at first light.
 
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luthj

Adventurer
Thanks for the input. I have not used this model myself, but it comes highly recommended. I have found Victron's tech support and documentation to be very good.
 

rayra

Expedition Leader
well that's one set of relatively 'top shelf' component choices, but there's nothing "inexpensive" about $1000 or having to buy specialty tools to complete a job. And soldering for such 'fixed' infrastructure is quite adequate. And crimping is harder to screw up for folks with no soldering / pipe sweating experience.
Pretty sure I did my comparable Aux and 1/0 cable runs and rear power module setup for about 2/3 the cost of your shopping list. But I'm a cheap bastard with too many hobbies to spread my limited cash across
 

luthj

Adventurer
Considering folks spend $400+ on a single battery, and get a tenth the performance, I think the value is there. I didn't say cheap, and obviously I was focusing on value. I have also done bargain basement builds for other and myself, but the time spend coddling them is not worth it to me at this point in my life.

Spending 40$ on the correct tool to make repeatable terminations is not much to ask for either.

I have personally sorted/diagnosed many poorly functioning installs with dead batteries and very unhappy owners. Poorly chosen, or cheap "china special" components are often the cause. Spending 10-30% more can prevent a fire too, seen that...
 
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utherjorge

Observer
I'm just reading this now, off of your other link. I appreciate it. Do you have any pics or a build thread where you "did" this?

EDIT: I just checked your build thread and saw pis, but didn't know if you had a separate electrical thread.
 

luthj

Adventurer
My current build uses a different component set (mostly). On a previous rig I set up a similar system using the GC2 battery type, 200W of solar, charging relay etc. I can probably hunt down a few pics.

That being said, this type of setup is going to be functionally the same as many other aux battery builds on this forum. It will have 2 batteries in series instead of one though.

I do have a thread over on sprinter-source with my electrical build out. Its pretty full featured with 600W of solar, induction cooktop, inverter etc. So not really applicable to this budget oriented thread.
 

trae

Adventurer
I'd love to see instructions for something like this:

The video has a parts list, but no battery specs (although 42 x 18650 at 24v is maybe 40amp hours at 12v if my math is correct)?
 

trae

Adventurer
Right off the hop, that guy is a ’tard calling that battery box a generator.
But I am the guy who calls my Landcruisers ’jeeps’ partly to ease conversation, also pissoff Toyota Fanbois.
Anyway, cant accurately answer because 18650 cells can vary in amphour capacity. Anywhere from about 3.2Ah down to zeroAh. http://englishrussia.com/2018/12/04/powerbanks-can-be-fake-too/
That’s a little harsh, no? There’s a whole category of battery boxes called “solar generators”. I agree it’s a misnomer.

Assuming each 18650 is 2500 what do you get?


Sent from my iPhone using Tapatalk
 

luthj

Adventurer
18650 cells are around 10 watt hours each. 42x10=420 watt hours. That is about 35AH for a 12v pack, or 17.5 for a 24V pack. Those cells are usually wired in a 7 series config for 22.4V nominal. So 42 cells total is 7s6p. That would yield a pack with 18.75AH at 22.4V nominal. When dealing with multiple output voltages (usb, 12v, AC/DC etc) it is best to stick with watt-hours, as energy is energy, but voltage can be changed.

While calling that pack a generator is not very accurate, there is an entire class of portable power packs called generators, solar generators etc. If you want to get web search hits, that's the best nomenclature to go with currently (sadly).

If someone wants to buy me the parts, I will happily build a box and post up a detailed how-to. Likely just pictures and wiring diagrams, as I find video too clunky for detailed stuff.

That box looks pretty clean, and the wiring looked well done as well. 420W hours is still a bit light for running a medium sized fridge. For portable electronics and lights, that would be good for many days.

Edit: those 18650 cells are about 5$ each? So that pack is going to be a bit pricey...
 
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Verkstad

Raggarkung
Assuming each 18650 is 2500 what do you get?
In that example of 42 LiPo 18650 cells to get 12V, the math wont work out right.
Assuming it series 4 cells to acheive nominal 12V, thats 10,5 groups of 4 series cells...
So lets just say its 40 cells. 10 groups of 4 series.
Each series will have 2.5Ah. Multiply by 10 = 25Ah.
 
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trae

Adventurer
18650 cells are around 10 watt hours each. 42x10=420 watt hours. That is about 35AH for a 12v pack, or 17.5 for a 24V pack. Those cells are usually wired in a 7 series config for 22.4V nominal. So 42 cells total is 7s6p. That would yield a pack with 18.75AH at 22.4V nominal. When dealing with multiple output voltages (usb, 12v, AC/DC etc) it is best to stick with watt-hours, as energy is energy, but voltage can be changed.

While calling that pack a generator is not very accurate, there is an entire class of portable power packs called generators, solar generators etc. If you want to get web search hits, that's the best nomenclature to go with currently (sadly).

If someone wants to buy me the parts, I will happily build a box and post up a detailed how-to. Likely just pictures and wiring diagrams, as I find video too clunky for detailed stuff.

That box looks pretty clean, and the wiring looked well done as well. 420W hours is still a bit light for running a medium sized fridge. For portable electronics and lights, that would be good for many days.

Edit: those 18650 cells are about 5$ each? So that pack is going to be a bit pricey...

Thanks, I came up with similar math. Point taken about W/hr rating.

In the video description, the author notes that he got his cells at a walmart sale at $1/pop. I think at that price is compares very favorably with something like Dakota lithium (https://www.electric-bike-kit.com/12v-lithium-lifepo4-replacement.aspx).
 

luthj

Adventurer
1$ each would be enough to motivate me to make a hand-built pack. Welding the cells up can be a pain though.

280$ would get you a pre-packaged unit with BMS/protection. Something like this.
https://www.bioennopower.com/collections/12v-series-lifepo4-batteries/products/copy-of-12v-30ah-lfp-battery-pvc-blf-1230w


A somewhat related 400w-hr power pack here. Pricing is not bad if the pack is quality. Note that the charge rate from a wall charger is only 80W. However I would guess that you could speed charging using a Dc-Dc supply in the right voltage through the external jump start port.
https://www.bioennopower.com/collections/mobile-power-station/products/400-w-hr-power-pack-bpp-m400
 
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