Hi, a halogen lamp has quite low internal resistance when cold: a near short. Therefore, the mppt sees it as a short and engages the short circuit protection.

Above is for when switching the load output on. The only thing to be done is work around it: power the lamp directly from the battery. And to use the load output algorithm then add a relay.

SUMMARY ON LOAD OUTPUT DETAILS AND LIMITATIONS

- in summary; the load output is designed for resistive loads; and it is short-circuit protected. Because of that it is not possible to power (sizable) halogen lamps from it; even though you might expect so when looking at the Amp-rating of the lamp. Halogen lamps draw a multitude of their rated continuous amperage for a relatively long time; tripping the short circuit protection (with reason; without it the mppt could get damaged)

- same for certain fridges; and also inverters (capacitive loads).

- see Solar Charger manual for how to wire an inverter directly to the battery and still switch it on/off with the load output

- same applies to other loads which

- the disadvantage of wiring loads directly to the battery is that you then can't see their current draw any more in the VictronConnect app; or other visualisation. To work around that; install a BMV battery monitor.

- some may ask if its possible to disable the short circuit protection: the answer is no; thats not possible. The design is nice for most systems; but indeed has limitations and thats just the way it is.

- after switching the load off when short-circuit is detected, it will retry within a few seconds. So when you have a load (a halogen lamp, or a fridge, or anything else), that is being switched off and on every few seconds, disconnect it and wire it differently.

I performed some tests today. Used a 21W car brake lamp and a 55W car headlamp as as test loads due to their high inrush current properties. Both are good old fashioned filament lamps of course. I have set the load output to "Always On"
I discovered that the MPPT will respond very quickly to overload events.

So I have an MPPT 100/20 with an AGM battery at its battery terminals, a fake solar panel in the form of a bench power supply with a big resistor (because there is no sun today).

I am measuring the current that the Load output is supplying with my oscilloscope over a 0.1Ω shunt resistor.

So, let's measure how much current is flowing through the Load terminals and how long the MPPT takes to shut it down.

Here is a capture of the 21W brake lamp:
You can see that the initial burst of current peaks at about 12A, the filament heats up and the current tails off gradually over the next 100mS. Good, no problems.

Let's have a look at the 55W car headlamp:
This time, upon connection of the lamp, the inrush current peaks at about 40A and finally after around 15μS the Load switches off and this is reflected in the VictronConnect App. A second or two after disconnecting the lamp, the Load output is turned back on. I repeated ths a couple of times with similar disconnection timescales.

With a lower overload current (two 55W filaments in series), the current peaks at like 25A and the MPPT gives it some more time to clear, but when it has not done so after nearly 80μS then it disables the Load output.

Here I have just short circuited the Load output:
The short circuit current peaks at over 60A, and would have kept going, with a disconnection time of roughly 5μS - give or take.

So what?
Well, it seems that there is some "leniency" built in to try and allow for high inrush currents, but where do you draw the line. Too much leniency and then things blow up, too much and nothing works. Inductive loads are notoriously tricky and it's almost impossible to characterize all possibilities out there. From a design perspective there is only so much that can be done to keep with the budget constraints. The answer is to tricky loads drive a relay from the Tx port function, but then there is no metering of the load.
I know how I would get around this problem, but I don't think it's everybody's cup of tea.

Thanks mvader and wkirby, very comprehensive answers and illustrates exactly what I was doing.

So wkirby, what would you do, something with a relay, maybe a delay type relay?

Ray

@WKirby : Sometims the easiest way to solve that problem in case of halogen lamps is with a simple NTC

@Peter Polz : Yes, that will almost certainly work and will probably be the simplest. However, an NTC is the one thing that I can't find at the moment, I'm still searching my "scrap PCB cache" for an old SMPS which will certainly have one. I'd like to demonstrate it and try it on a motor.

So far, I have had success with a large inductor in series with the lamp and also a fancy automotive high side switch with automatic current limiting (BTS5016).

Hey all, sofar it still looks like the load output complaints (not starting large halogen lamps, not starting fridges) are all due to limitations of today’s design. I mean it’s not some software bug that urgently needs fixing.

But; we could look to see if it can be improved. By for example using more modern fets in the load output; increasing the (start-up) current. Or for example by buying a often use fridge that doesnt work today, and then testing/tweaking the system (if hardware allows it) to make the Short circuit protection allow its startup.

some questions; to see if we should start such project:

- why use halogen lamps? I would use led lamps instead in my motor home; so I don’t see any reason to spend R&D time on halogen lamps. (?)

- what fridge / compressors should we buy? Which are the popular ones in which geographical areas?

Hi

This is the fridge i am currently using , that i am having the same issue with

https://www.nationalluna.com/product/nl-52-weekender-refrigerator

I've been using the 75/15 Bluesolar and Smartsolar on in vehicle installations with a fixed solar panel, Primarily running 12v fridges from the load output with no problems, I've been doing this for some time, and enjoy the consumption and yield data it provides. When the 100/20 was released I quickly purchased several to switch over to the 20a supply as this was preferred for faster charging. However, I too like so many of you found the load output would switch off, What I found was it would run fine for a period then stop. I had to return them all and continue to use the 75/15. I was advised by Victron through the Disqus page that it was related to inrush current however, The 75/15 work fine. I'm very keen to figure out why and have it rectified as I was told the 100/20 has exactly the same inrush and short circuit protection as the 75/15 . Keen to Follow

I believe this issue could be alleviated by using a large capacitor in series with an appropriate resistor to cap the capacitor charging current below the short-circuit protection limit. For example, if the limit is 20A and we're talking 24V, you should use a 1.2Ω resistor. That way, as soon as the charger output activates, the capacitor will charge up OK and then as soon as the compressor starts, the capacitor will provide the same 20A of current to the fridge.

Hi all,

A long long time later, but I wanted to let everyone know that we closed the loop on this one.

After this discussion on community, our hardware team looked into the design and found a hardware improvement to make: improving how the load output handles inrush currents.

We found that (in the old design) the load output resets under the following scenario: the fridge is already on, desired temperature is reached thus the compressor stops working. As soon as the compressor starts again, a peak current of about 40A is drawn which is enough to trip the short-circuit protection of the load output. Once the short-circuit protection trips, the load output switches off and after a few seconds switches back on again (thus the fridge resets as well). At that point the current drawn was lower (close to 22A), so the fridge was working ok.

We kept the fridge running for 4 days (testing with different battery voltages, temperatures and even with the option of turbo cooling) and the above behaviour kept repeating.

Following those results, we improved the design, it now allows a higher startup current. Which we tested with said fridges & compressors, and also Ray tested it, already back in June 2019. And conclusion is that it works well.

Here are the serial numbers per when the (hardware) change was implemented:

• SCC075010060R SmartSolar MPPT 75/10 Retail HQ1935
• SCC075015060R SmartSolar MPPT 75/15 Retail HQ1935
• SCC110015060R SmartSolar MPPT 100/15 Retail HQ1947
• SCC110020060R SmartSolar MPPT 100/20 Retail HQ1911

The 100/20 that we currently ship from our warehouses has the improvement. As do the 75/10 and the 75/15. The 100/15 is still shipping with hardware from prior to this improvement, due to stock levels of older production batches.