question

If the Battery Protect internal circuit design is how I think it is then no, it would not work in reverse.

Edit: I misunderstood the question, ignore my above comment.

@WKirby: thanks for your input.

I could think of a circuit design where it might work though. As we can only second-guess the internal design, I think only Victron could provide a definitive answer. Otherwise I just might try it.

I now tested it and it worked.

With Pin 2.1 connected to +12V current will flow in either direction, with voltage drop <0.1V. When disconnecting 12V input to Pin 2.1, Battery to Load is interrupted. Load to Battery is not, but now has a voltage drop of 0.6V. As expected for n-ch power MOSFET.

The remaining question is whether it will damage the BP over time / at higher currents. I tested at 12.4V and 1A.

Victron Energy advise this type of cabling when the charger can't be pilot by remote by the BMS so it will not damage the BP. And it's more efficient to use a BP than a Cyrix Li Charge so your system is good.

@MyShopSolaire: thank you for your feedback. Unfortunately I now have two contradicting statements, yours and an offline one by the VE distributor I bought the BP from who basically says doing this would be at my own risk. Not sure you noted the change I applied to the drawing, i.e. connecting "out" to "out" between the 2 BPs. Do you have knowledge of anybody using that setup?

@BenL: I assume you are right, also the BP data sheet says it uses MOSFETs. However I would strongly recommend not to apply nominal load to the BP in reverse direction while the BP is "off". Assuming a drop of 0.7V through the diode, at 200A it would generate around 150W of heat. I cannot imagine a unit the size of a BP220 handling this. Compare for example the size / weight / heat sinks of the Argo Diode products, which are Schottky.

In the meantime I tested the BP-65 at about 25% nominal load / 15A. With the BP "on", voltage drop in either direction is in the range of a few mV. With the BP "off", voltage in reverse dropped by 0.7V, as expected. Makes for around 10W. For < 1 minute this may be ok, the BP did not get very warm.

Anyway I will not move ahead with this layout for now. Without an official spec limit by VE on reverse current I take it to be zero. The risk of the BP later failing in "on" state due to prior damage from reverse current defeats the idea of battery protection.

@ stefan.cs Yes, we have already advised a similar use for the BP as load or load disconnection. It's a little different, it was for a lithium system, we have to use BP the Multiplus Compact does not accept the lithium assistant.

This installation dates from May 2018 and we had no bad feedback and it has been approved by one of our sales manager of our country.

And we have also sold many battery protect for similar uses of lithium instead of the Cyrix Li Load or Li Charge.

As these BP pass current both ways. ie in and out then all should be fine. it really does not matter which is in or out based on your diagram at all

the reason they have a in and out is ONLY to supply power from the IN (the in normally comes from the battery) to pin one via a resistor so that you can turn the unit on and off manually or to remotely override the off or low state of pin 2 by joining pin 1 and 2, plus the internal programming features.

otherwise there would be no need for a in and out at all.

It can also be turned on by battery voltage on both the in and out sides so its fully bi directional.

well thats my thoughts.

Coming back to my initial question, I now assume the following would work. The Agrodiode Isolator puts Schottky diodes in parallel to the BP's MOSFET reverse diodes. It will take the reverse current in case any of the BPs disconnects.

In principle, it should look like this:

I would achieve the same by connecting a BMS 12/200 battery minus and connecting charger and loads to LB, leaving AB disconnected. The reason I am trying to find a different solution is lack of adequate installation space for one large unit as compared to several smaller ones..

Hi

Ok, I get that the BP series is not *spec'd* to do this or that. I've sat through very long lectures from corporate lawyers about how you never ever "extend" the specifications on a product in conversations with a customer. Staying employed is a good thing. Liability lawsuits are to be avoided. I get all that.

So what happens if you *do* put a charger on the load side? The answer is that the world does not immediately come to an end.

Let's say you hook up a BP-220 on the bench and feed up to 5A through it. In the "correct" direction, the voltage drop is about 3/4 what it is in the "reverse" direction. Indeed the power dissipated into the heatsink *is* higher when run this way. It's not the "gigantically higher" sort of thing you would get from a 0.7V diode drop suddenly coming into the picture. You still are in the tens of mV sort of range.

So indeed, the ratings "backwards" most certainly are not as high as the ratings "forwards". Unless they re-write the spec sheet to reflect this, there's an issue. It most certainly can overheat at a "lower than expected" current level. That's not quite the same thing as "does not work".

Does the "derating" required go up as current increases? That's a good bet. Is the net result a 50% derating or is it higher than that? All the test above suggests is that you are ok at 2.2% of the 220A rating.

Why even bother with this insanity ( I freely admit it's a bit crazy) ? The proposed "use two in series" fix shown with the solar charger is fine if that's what you have. If you are running a Multi hybrid inverter / charger .... not so much. Thus the ongoing investigation .....errrr ... insanity ....

Bob

I wonder if the answer to this is a Cyrix Li load and a Cyrix Li charge wired in basic parallel then if the load control goes low the Multiplus can still charge via the Li Charge.

All,

I have some input into this discussion that is very important. I installed the BP100 in a system and connected the charging source to the load side as the original poster was asking about.

It resulted in a fire in the BP100 unit and nearly destroyed the vehicle. The situation was that the batteries (not Lithium) were in a low state 70% charge or so and the charge source (Xantrex Freedom inverter charger) went into bulk charge mode when connected to an AC source. It was putting in about 60A in the Bulk charge mode. I was elsewhere in the shop and after some period of time (maybe 20 minutes) I noticed smoke coming from the electronics area of the van. I disconnected the AC source and batteries as well as used an extinguisher to put out the burning plastic of the case of the BP100.

Clearly reverse current of 60A through the BP100 generated enough heat to damage the unit and start a fire.

I'm planning on installing a new BP100 unit and hooking all my charging sources (inverter/charger, solar and vehicle alternator) direct to the battery this time. At this point the BP100 a glorified battery cutoff switch because only my smaller fused loads will be disconnected from the battery if the battery reaches the cutoff voltage. One of the main reasons for the disconnect feature was to protect if the customer left the inverter on by mistake and parked the vehicle for a few days.

Anyhow, be careful with current flowing through the BP100 in reverse.

wow, so is there a tested limit from Victron? I mean you already allow for mill amps to power a charge controller in reverse at night as this is low enough heat in the BP to not be a problem. But a lot of people bought and wanted to use these in line where there is reverse current from time to time. So what is the safe limit of 10 amps? 30 ? or just milli amps?

please advice ( this does explain why I smoke one about 2 years ago and I could not figure out what happened to it, It was on an inverter charger and just stopped working one day ) ( no real smoke, in this case, was just a term )

I've been allowing my Victron 30 amp ( 100/30 charge controller ) charge controller to back feed through my BP-100 to charge my batteries. Now I have to redesign my system ...... wow would be great if Victron could make a BP series that can handle the reverse flow