Can you wire a compressor off a lithium battery?

 

The general consensus is that a compressor gets wired to the starter battery, this is what most manufacturers of the compressors will tell you, and they’re not wrong.

Wiring a compressor from the starter battery is the safe bet and the more logical option, but there are times when it isn’t practical.

During my 4WD build I faced some circumstances that meant it would be easier for me to power the compressor from my lithium battery, but first I needed to  decide: can you run a compressor from a lithium battery or not?

Fortunately after looking further into it I realised that in my case, I could run my compressor from a lithium battery, but every single install is different and results may vary.

In this post I will run through some of the reasons that  you might prefer to run your compressor from your lithium battery, the limitations to powering a compressor off a lithium battery and why it worked for me.

By going through the same checks that I did you can figure out whether you can wire your compressor to your lithium rather than your starter battery for your particular 12 volt setup.

*Affiliates Disclosure

Affiliate links are present on this page. Through partnerships with, but not limited to: Amazon, eBay and Commission Factory, I will make a small commission through qualifying purchases. This comes at no extra cost to you and is just a way for me to try and support myself and the blog.  Thank you.

My compressor needs

 

In this post I will use my own setup as the example, I bought the ARB twin compressor portable kit (eBay).

I went for the twin due to its 100% duty cycle and for the speed in which it would allow me to inflate my tyres. As a twin compressor though we have two motors, which comes with a higher power draw.

This is why I had to figure out, can you run a compressor from a lithium battery?

The lithium battery in question is not a massive one, I bought the Enerdrive 125Ah B-tec (eBay).

This for me was a good balance between usable power but with relatively low weight. So that is what I was working with and what the examples will be using, but obviously you just need to substitute the information for your components, which should be available on the company website (Enerdrive specs).

Can you run a compressor from a lithium battery – Install video

 

If you’d prefer to see my reasoning in video form (as well as the install) then this video below covers the same things this post will talk about as well as some advantages of ceiling mounting the compressor in the canopy.

Why not use the starter battery?

 

If you can, then go for it.

There are reasons that it might be impractical though for some 4WD setups. These are some of the main reasons I didn’t want to wire my compressor back to the starter battery.

 

Cable runs

For me the compressor was being mounted in the canopy which meant I would need long cable runs if I tried to use the starter battery.

As I was using a twin compressor that meant either running a single 2 gauge cable and splitting it at either end for fusing, or running two separate 4 gauge cables, which are still massive and expensive.

 

Costs

The volt drop issue comes into play here with long cable runs, which means to combat that large cables are needed. The install costs balloon out with cable, lugs, non-split tubing, dual wall heat shrink and cable glands.

Compressors costs hundreds or thousands of dollars, you don’t want to have to spend another $250 afterwards just to get the compressor wired up safely.

 

Suitable locations close to the starter battery

My engine bay was full, even if it wasn’t I wouldn’t mount the compressor there as it is bad for the life of the compressor to be surrounded by all that heat and then unable to dissipate its own generated heat.

The shorter the cable run the better with compressors, because you eliminate that voltage drop issue, but this is harder to achieve with the starter battery.

 

Unnecessary cable entries

Running a compressor from the lithium meant that there were no holes needing to be drilled for cables, which meant no water proofing was needed to keep the canopy free of dust and water.

Although the compressor fits here, it is too long a cable run and offers poor heat dissipation.

Can you run a compressor from a lithium battery – Checklist

 

Can you run a compressor from a lithium battery? Yes, if…

There are a few things to think about before you decide that you are going to run your compressor from your lithium battery, once you cover all these bases then you can proceed safely without the risk of blowing fuses, damaging your lithium battery or damaging your compressor.

Battery discharge rate

 

What is the battery discharge rate of your lithium battery?

As a rule of thumb, the batteries with the larger capacities tend to have a higher maximum and sustainable discharge rate.

Remember, we’re not looking for a peak discharge, the output needs to be sustainable as the compressor could be working for a few minutes!

There are exceptions to the rule with some smaller lithiums having higher discharge rates, which is a feature that will add cost, check out my lithium battery comparison post to compare battery discharge rates.

 

 

You might be able to see that the 125Ah lithium here has a maximum continuous discharge rate of 100 amps @25°C ±5°C for 30 mins.

To see how relevant this is we need to figure out what the compressor’s power draw is of course.

 

 

The maximum power draw of the compressor is 68.6 amps.

 

Things that favour the lithium

This means that the Enerdrive lithium has a headroom of 31.4 amps, but there is a little bit more here that works in favour of the lithium being able to handle the required 68.6 amps.

Firstly, that is the maximum draw, it is more likely to average between 55-60 amps of power draw and only when inflating non-stop. There will be times in between where the battery is “resting”.

Secondly, the lithium can handle 100 amps for 30 minutes (at about 25°C) whereas it is not likely that you will be inflating your tyres for any more than 5-10 minutes.

*Affiliates Disclosure

Affiliate links are present on this page. Through partnerships with, but not limited to: Amazon, eBay and Commission Factory, I will make a small commission through qualifying purchases. This comes at no extra cost to you and is just a way for me to try and support myself and the blog.  Thank you.

Total amp draw required from lithium

 

Although it’s great that there’s 31 amps of headroom there, what else is that lithium going to be powering?

If you have a big inverter you could get caught out by having someone running that simultaneously. Think of someone cooking food or making coffee while the car is pulled over to inflate tyres as a little meal break.

Using my setup as an example I had the following things to consider (affiliate links):

That is basically it.

The maximum the fridge draws is 4.5 amps, the inverter in theory can draw 50 amps if the full 600W is used, but when charging my Macbook pro (Amazon) it only draws 11 amps, the lights at their maximum draw about 6 amps.

So if for some strange reason all of the lights were on, while I was charging my Macbook Pro and the compressor was running that adds up to 90.1 amps.

So even after all of that, I could still charge the DJI Mavic 3 (Amazon) for example at another 7 amps without stressing the battery out for the duration of the compressors run time.

Where I can get unstuck though is if I or someone else uses the milk frother (Amazon) during inflation. This is the one thing I have in the car that actually draws all of the compressor’s power, thus tipping the battery over the discharge rate.

 

Built in safety factor

So although the above scenario is not going to happen out of sheer ridiculousness, you can limit the likelihood of these things happening in general by limiting the amount of power outlets you have in your setup.

For example, I have two outlets off the 600 watt inverter, I am limited with what I can plug in and I like it this way, no power boards in the car so everything gets charged by USB-C unless it absolutely has to use the inverter.

This works better as it limits the 230V being used which can be dangerous and also stops too many devices coming on a trip.

Cable sizing

 

Something that can catch you out in deciding if you can run a compressor from a lithium battery is the cables that you have used in your setup.

These are the outgoing cables, the active through a fuse and the main negative return path. In the image above you can see these cables in my setup, which goes through the Redarc BMS30 (eBay) battery shunt and how large they are.

The reason for this is that I had an idea that I would grow into the 12 volt system as I went and that I would eventually add more and more to the system, including larger inverters and possibly a compressor.

That meant that I massively upsized the cables here. The good news is that in a lot of 12 volt setups these cables are quite short and won’t be the most difficult to replace.

It’s not the difficulty though, it’s just making sure you’re aware that before you add a compressor to your lithium battery that you have cable sizes that can handle that large amount of power draw.

Fuse sizing

 

Once you’ve got your cables sorted, do you need to upgrade the size of your fuse before you can run a compressor from the lithium?

For me, I had already installed a 125 amp fuse into the ANL fuse holder (Amazon) that you see mounted to the top of the battery in the image above.

This fuse size must be smaller than the current carrying capacity of your main cable!

The idea here is that the fuse blows before the cable starts a fire, but after all of your accessories have been powered on. So size it to suit the combined load of all of your accessories, so long as that combined load is less than the cable can handle.

This 125 amps for me is enough for now, but it actually technically could blow if I was to have the inverter running the milk frother at the same time as the fridge was on and the compressor was running. So I need to look out for that.

However, with the AWG 2 cables installed I can up that fuse to 150 amps on that cable and be safe. I carry spares with me for 125 amps and also 150 amps as well (for another ANL fuse in the engine bay).

Closing thoughts

 

Now, can you run a compressor from a lithium battery? I can.

But deciding if you can run a compressor from a lithium is for you, using your setup, your cable sizes, your compressor and your lithium batterie’s specifications.

Limitations to running a compressor from your lithium

 

Just because you can run a compressor from your lithium doesn’t mean it is the best option. I had other things at play when deciding where to power the compressor from.

I had limited cable entries in the canopy, didn’t want to waterproof everything, didn’t want to have these massive cable runs and more, there was a bit to consider.

There are ways in which the lithium powering the compressor is not a good idea.

Losing amp storage – Test results

 

Remember that the lithium is the power for your fridge, camp lights, water pumps and whatever else might rely on it. So be careful with how far you go, don’t go airing up an entire convoy and selling yourself short on power.

I did a test with the car off and filled 4x 265/65/R17 tyres from 15PSI to ~38PSI using a total of 7.5 amps.

So even with reasonably small tyres it does take away from your power. The good news is that after you are inflating it is usually because you’ve hit the bitumen and will be driving for a bit.

For me using the Redarc BMS 30, it can do 30 amps in an hour, this means that in 15 minutes it will put that 7.5 amps back, so not too long a drive for me to replenish the lost power.

Engine on

 

When the compressor is off the starter battery you always have it running. You need to stay in that mindset even when you run the compressor off the lithium.

It might only be small, but the car at idle is charging that lithium and filling up what is taken out (the speed of which depends on the car output at idle and the DCDC charger you chose), so just leave the car on as you would. There is a temptation to switch it off with the lithium doing the work.

Conclusion

 

Can you wire a compressor from a lithium? Sure you can, but make sure it is safe to do so first in whatever your particular setup is.

Try to have heaps of headroom if possible and not push the limits of the battery or the cables that supply it and then the compressor will run better for longer.

The good news is that there aren’t too many compressors that will draw more than a twin compressor, so if you’re using a single compressor than you will likely have way less power draw to worry about.

The biggest trap here is large inverters running at the same time as a compressor and running things like microwaves, kettles, coffee machines and other high power accessories.

Thanks for reading, comments welcome.

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