am I missing something cant seem to find a bms that would work well in rv.

[NEWYORKHILLBILLY]

I am kinda new to this so maybe i overlooking something,But i cant seem to find a Bms with low temp shut off that will only shut down charging and let you still draw power to load. I know the battlel born battery will do this. so this must exist
Here is my planed system 280Ah 4s 12 volt battery 500 watt solar victron 100/50 scc. installed in small trailer with wfco 55 amp converter. no inverter at this time.

my other question is there a way to keep power to the MTTP if the bms disconnects ?
would a common port or separate port work better for this system ?

 

[FilterGuy]

What is the max expected load current? If it is low enough, this BMS should do what you want.
https://www.aliexpress.com/item/4000776528805.html?spm=a2g0s.9042311.0.0.7cf74c4diUk9kd
(Note: @OverkillSolar has a US stock of these. You might want to contact him)

This BMS has what I call a hybrid port. It shuts off charge and discharge separately.

 

[mkaye]

You will have to upgrade the wfco 55 to something that understands lithium. I upgraded mine to a progressive dynamics. I can move a jumper over for lithium. Chargery bms controls 2 relays, load and charging

 

[NEWYORKHILLBILLY]

You will have to upgrade the wfco 55 to something that understands lithium. I upgraded mine to a progressive dynamics. I can move a jumper over for lithium. Chargery bms controls 2 relays, load and charging

Ii was hoping not to have relays. if i can find a bms with separate charging with a good amp rating charging circuit i should be able to avoid the relays

 

[NEWYORKHILLBILLY]

What is the max expected load current? If it is low enough, this BMS should do what you want.
https://www.aliexpress.com/item/4000776528805.html?spm=a2g0s.9042311.0.0.7cf74c4diUk9kd
(Note: @OverkillSolar has a US stock of these. You might want to contact him)

This BMS has what I call a hybrid port. It shuts off charge and discharge separately.

so this unit would not shut off charge in a low voltage case. so my mptt controler would not lose power?

 

[OverkillSolar]

so this unit would not shut off charge in a low voltage case. so my mptt controler would not lose power?

Things do get weird when the BMS cuts off at either end. If discharging is cutoff for low voltage, your MPPT charger can still charge but the problem is the loads are still connected, and the charger will probably not start up in the morning.

In a perfect world the loads and the chargers will behave and shut off when appropriate.

 

[dashdrum]

What is the max expected load current? If it is low enough, this BMS should do what you want.
https://www.aliexpress.com/item/4000776528805.html?spm=a2g0s.9042311.0.0.7cf74c4diUk9kd
(Note: @OverkillSolar has a US stock of these. You might want to contact him)

This BMS has what I call a hybrid port. It shuts off charge and discharge separately.

I'm a little confused here (situation normal). Without separate ports for charge and discharge this unit is able to turn off charging while still allowing use? Or vice-versa? Or will it just kill the connection for all when any of the limits are exceeded?

 

[FilterGuy]

I'm a little confused here (situation normal). Without separate ports for charge and discharge this unit is able to turn off charging while still allowing use? Or vice-versa? Or will it just kill the connection for all when any of the limits are exceeded?

Yes, It can turn off charging while still discharging or turn off discharge while still charging. I have a couple of these and they do work that way. What I have not done is set up a stress test and run them at full load for an extended time. That brings up one word of caution: A lot of folks think you should NOT run them continuous at their specified amperage. Some folks even say to cut the rating in half. Others say you can run them at 75%. Maybe @OverkillSolar can weigh in on this.

 

[NEWYORKHILLBILLY]

Yes, It can turn off charging while still discharging or turn off discharge while still charging. I have a couple of these and they do work that way. What I have not done is set up a stress test and run them at full load for an extended time. That brings up one word of caution: A lot of folks think you should NOT run them continuous at their specified amperage. Some folks even say to cut the rating in half. Others say you can run them at 75%. Maybe @OverkillSolar can weigh in on this.

Is this the case with all common port Bms or just this one? say compered to the daly common port. Like dashdrum I was surprised this one worked that way. Then i got thinking maybe they all do. Or is this because of the hybred port you mentioned ?

 

[FilterGuy]

I certainly can't speak to 'all' BMSs.

• This BMS works this way.
• The ANT BMS works this way.
• The Smart Daly BMS appears to work this way (I have not seen a review of it but the documentation implies it)
• The Chargery can work this way, but if you have a device that does both charge and discharge it might be difficult to set it up to work this way.
• I don't know about the regular Daly BMS.

It is becoming common enough that I would not use a BMS that does not allow the Charge and Discharge to be managed separately.

 

[NEWYORKHILLBILLY]

I certainly can't speak to 'all' BMSs.

• This BMS works this way.
• The ANT BMS works this way.
• The Smart Daly BMS appears to work this way (I have not seen a review of it but the documentation implies it)
• The Chargery can work this way, but if you have a device that does both charge and discharge it might be difficult to set it up to work this way.
• I don't know about the regular Daly BMS.

It is becoming common enough that I would not use a BMS that does not allow the Charge and Discharge to be managed separately.

Thanks . I learning slowly I did send overkillsolar a message about his bms. I am kinda between his and the new daly smart. I dont have a inverter But might add one and the new daly smart bms has some high current models . That may be a benefit down the road. I been following the tread on both this one and the new daly smart. I concerned the new daly might be over my head tech wise. I need a plug and play for my 4s system. I just got my cells ordered . I assuming shipping on those will take a lot longer than a bms. It also looks like they have specs for a daly 4s separate port ,but i haven't seen it listed yet.

 

[FilterGuy]

and the new daly smart bms has some high current models .

That is my interest in them as well.

 

[OverkillSolar]

That is my interest in them as well.

How High?

 

[FilterGuy]

I ordered the 250 Amp version.....

 

[Dzl]

This BMS has what I call a hybrid port. It shuts off charge and discharge separately.

@FilterGuy, can you explain what you mean by hybrid port or point me in the direction of an explanation? How does it differ from a separate port BMS?

 

[FilterGuy]

@FilterGuy, can you explain what you mean by hybrid port or point me in the direction of an explanation? How does it differ from a separate port BMS?

Let me start by noting that there seems to be different definitions around the term 'common port'.

Some believe that common port means that 1) Both charge and discharge is done on the same wire and 2) Both charge and discharge are turned on or off together (You can not charge while discharge is turned off and you can not discharge while charge is turned off). What this means is that you have to physically intervene to correct an undercharge or overcharge event.

The BMSs that I have experience with all charge and discharge on the same wire, but charge and discharge are controlled separately. Consequently, even if the BMS has disabled discharge, it will still allow charging (and vise versa). I used to call this common port but since there seems to be confusion (and for lack of a better term), I have been calling this 'hybrid port' to clearly differentiate it from the old common port definition. If someone has a better term for it, I will gladly adopt it.

 

[Dzl]

Let me start by noting that there seems to be different definitions around the term 'common port'.

Some believe that common port means that 1) Both charge and discharge is done on the same wire and 2) Both charge and discharge are turned on or off together (You can not charge while discharge is turned off and you can not discharge while charge is turned off). What this means is that you have to physically intervene to correct an undercharge or overcharge event.

The BMSs that I have experience with all charge and discharge on the same wire, but charge and discharge are controlled separately. Consequently, even if the BMS has disabled discharge, it will still allow charging (and vise versa). I used to call this common port but since there seems to be confusion (and for lack of a better term), I have been calling this 'hybrid port' to clearly differentiate it from the old common port definition. If someone has a better term for it, I will gladly adopt it.

Okay, I think I understand. I never thought of the terms as ambiguous until now, but now I see how they can be.

I think your term makes sense, since its what many people would consider a common port BMS that behaves like a separate port BMS (based on my understanding of the terms).

Is it basically just daly that makes this distinction common vs separate? I don't recall if I've seen any other BMS' that make that distinction.

 

[NEWYORKHILLBILLY]

Let me start by noting that there seems to be different definitions around the term 'common port'.

Some believe that common port means that 1) Both charge and discharge is done on the same wire and 2) Both charge and discharge are turned on or off together (You can not charge while discharge is turned off and you can not discharge while charge is turned off). What this means is that you have to physically intervene to correct an undercharge or overcharge event.

The BMSs that I have experience with all charge and discharge on the same wire, but charge and discharge are controlled separately. Consequently, even if the BMS has disabled discharge, it will still allow charging (and vise versa). I used to call this common port but since there seems to be confusion (and for lack of a better term), I have been calling this 'hybrid port' to clearly differentiate it from the old common port definition. If someone has a better term for it, I will gladly adopt it.

I like the term hybrid port I think this will stick. so in a hybrid port will the SCC still lose it operating power in a fault situation? This is one reason that i was looking at separate ports . ( i believe but am not sure in a separate port the SCC would retain it operating power in a fault) It seems on the daly in the past the the problem with separate ports have been the limited charge current. But on the 2020 models at least they tell me its 50 amps charge current on all models and can be increased . If this is true this would be ideal in my case. I been talking with there store about adding a low temp cut off witch they say can be done. I was looking on the non blue tooth version. what concerns me about the new smart model is its programming, I am new at this and think it might be over my head . of course the ability to change this would be a big plus if you know what your doing.

 

[Tball]

I ordered the 250 Amp version.....

FilterGuy, do you mind providing a link please? This it? https://www.aliexpress.com/item/400...earchweb0_0,searchweb201602_,searchweb201603_

 

[FilterGuy]

FilterGuy, do you mind providing a link please? This it? https://www.aliexpress.com/item/400...earchweb0_0,searchweb201602_,searchweb201603_

Yup. that is what I ordered..... Once I get it and play with it I will report back what I learn.

 

[FilterGuy]

will the SCC still lose it operating power in a fault situation?

I am not sure what you are asking.

 

[NEWYORKHILLBILLY]

I am not sure what you are asking.

I told on the Victron solar controller you should never have the panels hooked up when you don't have the controller hooked to power or it will be damaged. so my question is in the hybrid BMS will it still l work if the load current is shut off on low voltage? I think it will in a separated BMS but i not even sure of that.

 

[FilterGuy]

so my question is in the hybrid BMS will it still l work if the load current is shut off on low voltage?

In direct answer to the questions: I don't see why not. However, keep in mind that if the BMS detects over-voltage you will still have the SCC hooked up while the battery is not.

I told on the Victron solar controller you should never have the panels hooked up when you don't have the controller hooked to power or it will be damaged.

A lot of people take this as an undeniable fact for all SCCs. Others say it is just plain wrong. I can't say definitively, but I lean toward the camp that says the premise is wrong.
1) I have a hard time thinking of how the circuit would be damaged.
2) Because of the over-voltage possibility, you could never use a SCC with a BMS without some other protective disconnect of the solar.
3) A while back @Will Prowse said he tried disconnecting batteries on his various SCCs and could not get any of them to fail.

Specific to Victron:
4) Victron makes rock solid equipment. It seems unlikely they would leave this as a possible way to damage the device. In fact, if you build an all-Victron system (including a Victron LiFePO4 battery), you could have the BMS disconnect the battery while the SCC is still charging.

 

[Dzl]

I can't say definitively, but I lean toward the camp that says the premise is wrong.

I can--well I can't, and if I ever do start saying things definitively y'all should ignore me as I'm nowhere near informed enough to be sounding definitive about much of anything... Buuuuuuuuut I feel pretty confident the premise is wrong. Here is why:

• Logically, a fuse, or a breaker, or a BMS disconnecting is functionally the same as disconnecting your SCC from the battery while still connected to the PV array. If disconnecting the SCC from the battery was a problem, then using an OCP on the circuit would be a problem and using a BMS would be a problem yet those are standard practices.

BUT as I said before, as soon as I start feeling confident and definitively saying things, its time to ignore me , so if this was my only evidence you would be right to take it with a grain of salt. However here is why I am confident, that at least with Victron controllers, its a non-issue:

• I asked @Justin Laureltec [authorized Victron tech] about this issue here and here is what he said:

Can anyone (@Justin Laureltec maybe) clarify whether Victron specifically cautions or prohibits placing breakers or switches between the battery & SCC?

Can confirm that they don't actually care, and in fact require a fuse or breaker between the SCC and the battery. Technically the wording is in there because of a conceptual problem on paper that they wanted to make sure would never happen, but this was written before the days of LFP and BMS systems and all that. Their own systems now will shut off the battery when necessary, which would obviously create the very problem that they're trying to -theoretically- avoid.

I too have tried really hard to make a Victron SCC fail in this way, under various conditions including the full-bore-charging sudden disconnection event that the wording was theoretically written to avoid, and I have never managed to cause a problem by doing this.

The official word from Matthijs [CEO at Victron] on this is that no one has ever heard of this condition actually causing a problem, it's just that an engineer back when his dad was originally developing these decided to include the language to cover for a theoretical problem that has never, in anyone's experience, actually occurred. With that in mind, they've been going through and slowly updating manuals accordingly... there definitely used to be some stronger language in the manuals that's now being removed (can't guarantee it's out of all the manuals yet) with only the language about connecting the battery first being left in - and that's just so the units can recognize and set the system voltage.

In my mind, this pretty much puts the issue to rest with Victron SCC's

 

[NEWYORKHILLBILLY]

In direct answer to the questions: I don't see why not. However, keep in mind that if the BMS detects over-voltage you will still have the SCC hooked up while the battery is not.



A lot of people take this as an undeniable fact for all SCCs. Others say it is just plain wrong. I can't say definitively, but I lean toward the camp that says the premise is wrong.
1) I have a hard time thinking of how the circuit would be damaged.
2) Because of the over-voltage possibility, you could never use a SCC with a BMS without some other protective disconnect of the solar.
3) A while back @Will Prowse said he tried disconnecting batteries on his various SCCs and could not get any of them to fail.

Specific to Victron:
4) Victron makes rock solid equipment. It seems unlikely they would leave this as a possible way to damage the device. In fact, if you build an all-Victron system (including a Victron LiFePO4 battery), you could have the BMS disconnect the battery while the SCC is still charging.

I emailed victron on this. They did confirm it will not damage the mppt controller to have the panels hooked up while with no battery power . I also learned something new . "battery voltage must be set at fixed instead of auto.
Auto voltage means the mppt is guessing which battery is connected by looking at the voltage
If the battery is not connected it can be guessing wrong, so after the battery is re connected then there is the in correct charge voltage."
so what i get out of this is if your using a victron mppt you be wise to turn battery voltage to the fixed position.