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Fra avatar image
Fra asked

Why smartsolar do not have BATTERY REVERSE POLARITY PROTECTION?

I was a little disappointed after discovering that my new mppt smartsolar 100/30 DOES NOT HAVE BATTERY REVERSE POLARITY PROTECTION.


This is very strange in fact The Chinese medium quality controllers (like epever or helios etc ..) have this protection and cost half the price of victron.


Even the top quality American MORNINGSTAR mppt controllers have this protection. (Only in the medium power models 25 / 40A, but not in the 60A models)


I wonder why Victron chose not to integrate this basic protection. What is the point of putting the protection against PV REVERSE POLARITY and not putting BATTERY REVERSE POLARITY?

Also I would like to understand why the smaller versions of smartsolar have a replaceable fuse while the larger versions do not have one and are irreparably damaged.

MPPT Controllers
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4 Answers
Alexandra avatar image
Alexandra answered ·

@FRA

You can reverse polarity connect the battery, as long as you did not connect the pv and switch it on.

All that will happen is nothing switches on. At that point you should see there is a problem and correct it. Also one of the reasons the manual instructs the correct procedure is a battery connections first.

If you then reverse the pv (and the battery is correct) you will also not blow anything. The charger just gets a bit warm and no charging happens. Again you should be checking and this too can be corrected without a problem.

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Fra avatar image Fra commented ·

Yes thank you. Is not a big problem for me. I check ever all, before make connection or switch on Pv breaker. But many people don't have a breaker on Pv wires in RV system and immediately the controller start when Pv are connecteds.

I only wonder waht is the practical or technical reason to not integrate a total reverse polarity protection, as the majority of other brands do.

Another question is: protect a 30A fuse nearly positive of the battery the smartsolar 100/30 in case of battery reverse polarity and Pv switch on??

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Alexandra avatar image Alexandra ♦ Fra commented ·

@FRA

Have you tested the reverse polarity protection on the other brands?

And can't answer for poor installation choices? Disconnecting panels under load is pretty dangerous and should never be done.

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Trevor Bird avatar image
Trevor Bird answered ·

I have not designed an MPPT controller but can consider what reverse polarity would look like. To me it would be a high current diode on the PV input to ensure reverse polarity was never applied to the switching circuitry. That means for the life of the device you have a voltage loss of 0.7 volt on the input. You may argue that the loss is minimal and of no concern. Others, like me would rather not have the diode forward bias voltage loss and just install it correctly. It is a compromise between losses and being idiot proof. Perhaps the cheaper devices consider their target audience and prefer the loss.

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wkirby avatar image
wkirby answered ·

Like trevor-bird said, reverse polarity protection causes losses. Simple diode type protection is very lossy and the heat would need to be dumped somewhere, your controller would get vey hot with roughly 30W being wasted at a 30A charge current.

MOSFET type reverse polarity protection is a lot less lossy, but a lot more expensive. There are still losses though. It seems wasteful to include additional expensive circuitry to protect against poor installation techniques. Then once installed the protection circuitry would never be engaged and just sit there wasting energy.

The higher the current, the higher the exponential loss. This would explain why higher current devices from other brands omit the protection circuitry.

The PV input does not have reverse polarity protection. It's simply down to PV short circuit current (usually 8A per string) is not enough to damage the controller, the controller just gets hot.

A fuse will not protect the controller. A fuse lacks the ability to read into the future and open up before a fault occurs. A fuse goes open after a fault has already occurred and prevents the wiring from melting.

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Fra avatar image Fra commented ·
Yes. In fact morningstar put reverse polarity battery protection in mid power controller, but not in high power controllers.
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Fra avatar image
Fra answered ·

Thanks you for the detailed explanation.

Aniway, I open many epever tracer controller and seems to have a mosfet and not a diode. I'm. Not sure if is for reverse polarity, but I'm sure that they are many mosfet. And the voltage drop to the battery terminal is 0.04v with 15 amp current.

Also morningstar i think use mosfet and not a simple diode.



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