System cutting out and restarting when using 12v DC outlet device

I'm having a strange issue with my newly rewired van solar system where all connected devices briefly turn off and back on again when I power on a 12v air pump connected to one of the DC outlets.

The air pump max power draw is 160w but the PSI value is adjustable so I only use it at a lower draw. When testing, I turned on my cabin LEDs (which are only drawing just over 1 amp) and when I start the pump everything cuts out for a couple of seconds before turning back on, but the pump will not run. I tested the pump separately using a 12v lab power supply and it runs fine, with a max current draw of about 6-8 amps when set to my desired PSI value.

My setup is very basic and as follows:

• 100ah 12v lifepo4 battery with JBD bms
• Victron smart solar mppt 100/20
• 12 way fuse board wired to the load terminals of the victron controller
• A few low power 12v devices i.e. 12v fridge, LEDs, USB, DC outlets, diesel heater

The DC outlet in question is wired with 12 awg and has a 20 amp blade fuse. It works perfectly fine when I tested with a cigarette lighter USB charger, but for some reason is unable to handle the air pump.

My guess is there is something being tripped in the BMS but I can't see any info in the app to indicate this.

I'm relatively new to the world of 12v solar systems and would appreciate any thoughts or suggestions!

Without numbers or testing I would guess the compressor motor startup surge is more then the battery can handle. You would need an amp meter that can measure the inrush to know for sure. Unless, maybe the compressor manufacturer can give you those numbers?

Q-Dog said:

Without numbers or testing I would guess the compressor motor startup surge is more then the battery can handle. You would need an amp meter that can measure the inrush to know for sure. Unless, maybe the compressor manufacturer can give you those numbers?

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The 12v lab power supply I used to test the pump has a max output of 10 amps so I would think that it wouldn't be more than this. I didn't notice any influx above this when watching the amp display on the power supply but I guess it could also be too quick to be displayed

The lifepo4 battery is rated for 100a Max discharge and peak discharge of 200a for 5 seconds so don't see why this would trip it either

Can't imagine you are tripping the BMS overcurrent protection, what's the wiring like between the battery and the fuse block? Pictures can sometimes allow someone here to see a problem you might have missed.

wpns said:

Can't imagine you are tripping the BMS overcurrent protection, what's the wiring like between the battery and the fuse block? Pictures can sometimes allow someone here to see a problem you might have missed

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Sure, I'll get some pics tomorrow.

For reference, wiring goes Battery > charge controller > fuse block. The fuse block also having and being used as the negative bus bar.

The current is limited on the load port of your controller. It is not normally used, wire your fuse block to the battery.

Whinny said:

The current is limited on the load port of your controller. It is not normally used, wire your fuse block to the battery.

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D'oh!!! I completely missed this. The load port is limited to 20 amps.

Q-Dog said:

D'oh!!! I completely missed this. The load port is limited to 20 amps.

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Yeah I do understand that load port is limited to 20 amps but chose to do this as I didn't expect to be using more than 15 at any given time. It also allows me to track the load outputs without needing another device.

Do Victron controllers have another method of load protection other than just the fuse to prevent loads over this limit? The blade fuse that I can see in the controller is 25 amps but obviously this is not blowing

I can possibly look to just route the DC outlet directly to the battery using an inline fuse if this does turn out to be the issue

Ah ok, I did another quick search and found this super helpful thread: https://community.victronenergy.com/articles/2992/load-output-of-mppt-charge-controllers.html

The controller does in fact have an extra safety method to prevent blowing the fuse in cases of high inrush current. It acts so fast that none of my testing devices are able to perceive it.

So looks like I will need to either direct wire my fuse board or at least have a separate circuit for these higher inrush devices