BlueSolar 75/15 won't drive inverter

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mspohr asked Aug 28, '19

BlueSolar 75/15 won't drive inverter

I have BlueSolar MPPT 75/15 connected to a LiFe 12v battery.

I tried to attach a 300W Bestek sine wave inverter to the "Load" terminals of the BlueSolar but as soon as I plug it in, the Load switches to "Off" and no power to the inverter. The inverter is turned off and has nothing plugged into the outputs. I notice an occasional 0.1 amp spike in the "trend" tab. As soon as I unplug the inverter, the Load switches back on.

Battery is fully charged 13.7 v and the voltage doesn't change when I plug in the inverter.

I can attached the inverter directly to the battery and it works just fine.

Can the BlueSolar be used with the inverter? I'd like it to manage the inverter load.

inverter current draw

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eduardo-kang answered · Sep 03, 2019 at 10:52 AM

I had a similar issue with driving a three amp fan from my load output on my 75/15. The MPPT would click, but the fan didn’t turn on. I didn’t dig into the cause, I just assumed it was due to a burst draw of power from the fans initial startup (inrush). The fan worked fine directly connected to the battery, however, this was at a remote site and I wanted the MPPT to prevent the load from draining the battery too far.

I initially fixed the problem by using an Bosch type auto relay - the load output on the MPPT would close the relay and connect the fan directly to the battery and open the relay when the battery voltage got too low. This got around the inrush issue and protected the battery from being drained too far, it just didn’t track power usage vs generation.

I ended up doing some digging and saw the inrush issue may be solved by using a “soft starter”. There was a video on YouTube where the same issue was described with the same MPPT. I lacked the expertise to build a soft starter so I looked to buy one. I ended up buying a dc motor controller with a built in soft starter for $12. I put the controller inline between the MPPT and fan, and set it to 100% speed and it remedied the issue. I’m sure it’s not the most efficient use of power, but it works.

My system is 12v so I’m limited to a max draw of 180w from the MPPT load output. The soft starter solved the problem with inrush, but it will not work if the inverter continuously draw more wattage than the MPPT supports.

Good luck.

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mspohr commented · Sep 03, 2019 at 02:01 PM

Thanks. I'll look into a soft starter. It would be nice to have the power consumption monitored.

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chuyskywalker commented · Jun 21, 2021 at 03:29 AM

Thanks for this info; I have the same setup as mspohr.

The weird part about this is that it only happens when you're connected to a battery. I had the inverter and charger for a week before my battery showed up and with just those two items connected, I could run the inverter without issue, as long as there was enough sunlight.

Gonna pick up their battery protect relay'ish block for my purpose here.

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Answer 1 · 2019-08-29T01:32:02Z

ceriw answered · Aug 29, 2019 at 01:32 AM

It sounds like the inverter pulls more than the 50A peak that is supported on the load output during startup. even if it started up, 300W at 13V is well over the 15A continuous limit of the load output.

You could use the load output to power a relay coil that then switches the inverter?

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Answer 2 · 2019-08-29T13:07:16Z

mspohr answered · Aug 29, 2019 at 01:07 PM

The inverter is turned off so it shouldn't be drawing any current.

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Answer 3 · 2019-08-29T20:22:05Z

mspohr answered · Aug 29, 2019 at 08:22 PM

Also tried another inverter. A 200W. Same result. Victron shuts down the load as soon as it's connected. Inverter is turned off and nothing connected.

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ceriw commented · Aug 30, 2019 at 06:05 PM

The inrush current of connecting the inverter (caps charging inside) is likely to exceed the 50A limit

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Answer 4 · 2019-08-30T20:01:06Z

Justin Cook answered · Aug 30, 2019 at 08:01 PM

Inverters should always be either connected directly to the battery, or directly to a busbar that is connected directly to the battery. The "load" terminals on an MPPT are expressly *not* for powering high-draw devices; per Victron's own documentation the load outputs should be used for low-draw devices such as lights or fans or such that you would like to have configurable to shut off at preset low voltages and/or when the sun goes down.

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Answer 5 · 2019-08-30T21:38:58Z

mspohr answered · Aug 30, 2019 at 09:38 PM

I think I have this figured out. It appears that the inverters, even when "off", must have a capacitor which charges up when plugged in. It appears that the controller tests the load by sending out 100ma of current and measures the impedance. If the impedance is too low, it shuts off the load. It will keep retrying but never enough to charge up the capacitor. This probably could the "fixed" in software but they probably don't want to do that for various reasons.

The instructions say at "some" inverters may not work and may need a relay which is what it appears I will have to do.

Thank you to everyone who responded. I appreciate your help.

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