Inverter charger with separate port BMS

[Yinks]

Hello, can anyone help me, I've got a separate port BMS and have an inverter charger, do connect mains electricity to the inverter and connect it to the load of the BMS?

 

[FilterGuy]

I am not following your question. Could you provide a diagram and specific part numbers?

In general, a separate port BMS is best suited to situations where the charge and load are separated. With an inverter/charger you will probably have to tie the charge and discharge ports of the BMS together and feed it to the inverter/charger.

 

[Yinks]

I am not following your question. Could you provide a diagram and specific part numbers?

In general, a separate port BMS is best suited to situations where the charge and load are separated. With an inverter/charger you will probably have to tie the charge and discharge ports of the BMS together and feed it to the inverter/charger.

Thanks, it's a Daly 8s, 100A separate port. I also have to connect input from solar panels. If I tied the ports together won't it overload the charge port as it can only 50a max?

 

[FilterGuy]

I do not have experience with Daly separate port BMSs so take what I am about to say as conjecture/extrapolation. If I have it wrong I hope someone jumps in and educates us both.

Presumably the Daly ports are unidirectional. (i.e. Load current won't flow from the charge port and charge current won't flow through the load port. Consequently, tying the ports together should not be an issue with load current overwhelming the charge port.

However, you may have a problem if the combined charge current of the Inverter/Charge and SCC is greater than the 50A limit of the BMS. Can you set the inverter/charger to limit the charge current?

 

[FilterGuy]

However, you may have a problem if the combined charge current of the Inverter/Charge and SCC is greater than the 50A limit of the BMS. Can you set the inverter/charger to limit the charge current?

Does anyone know what the '50A Charge limit' on the Daly BMS means?
Does it mean if you exceed 50 amps it will damage the unit?
**OR**
Does it mean the BMS will limit the charge current to 50 Amps?
**OR**
Does it mean it will detect an error and shut off charging if it goes above 50 Amps?

@Will Prowse used a lot of Daly BMSs back before we got so many options..... I hope he might know.

 

[Yinks]

Does anyone know what the '50A Charge limit' on the Daly BMS means?
Does it mean if you exceed 50 amps it will damage the unit?
**OR**
Does it mean the BMS will limit the charge current to 50 Amps?
**OR**
Does it mean it will detect an error and shut off charging if it goes above 50 Amps?

@Will Prowse used a lot of Daly BMSs back before we got so many options..... I hope he might know.

Just checked the inverter charger and it outputs be 10 and 70amps, would like to know if connected to the load port of the BMS, will it charge the batteries?

 

[FilterGuy]

Would like to know if connected to the load port of the BMS, will it charge the batteries?

Since I am not a Daly expert I can't say for sure, but it would be very odd if it worked that way. If it did, what is the point of having a separate charge port?

 

[Yinks]

Since I am not a Daly expert I can't say for sure, but it would be very odd if it worked that way. If it did, what is the point of having a separate charge port?

Thought so too. I've however contacted the store I bought the BMS, waiting to hear back. Grrr!! Should have just bought a common port.

 

[John Frum]

Thanks, it's a Daly 8s, 100A separate port. I also have to connect input from solar panels. If I tied the ports together won't it overload the charge port as it can only 50a max?

I've been running charge current through p- for monthes on my daly.
Not sure if I have overvoltage protection but it works.

 

[Yinks]

I've been running charge current through p- for monthes on my daly.
Not sure if I have overvoltage protection but it works.

Is it a separate port BMS

 

[John Frum]

Is it a separate port BMS

yes

 

[FilterGuy]

I've been running charge current through p- for monthes on my daly.
Not sure if I have overvoltage protection but it works.

Interesting.

It appears that you can put a reverse current through FETs in the BMS. (That is the way some of the hybred port BMS's seem to work.) You can get away with this for lower currents but if you tried to charge through the discharge port at a high amperage, things could get dicey. Either way, the BMS is operating in an unspecified way so knowing what level of current is 'safe' is very difficult. @BiduleOhm could probably add some detail here. He seems to have a strong understanding of analog circuit design and the various components. He reacted pretty negatively when we discovered a hybrid-port BMS that worked that way. (This is similar to running current backwards through the FETs of a Victron Battery Protect that @Will Prowse did in one of his builds. The build worked but Victron was adamant that it was a fire danger and was a completely unsupported configuration of the product. Consequently, Will changed the design.)

It would be interesting to know if there is over-voltage protection when charge current is run through the discharge port. I would guess not, but I am just speculating on how the Daly is designed. My guess is the BMS will turn off the charge port, but since it is charging through the discharge port, turning off the charge port may not do much. Make sure the inverter/charger is set to a safe charge profile. Also, if possible, set the inverter charger to something lower than the 60Amp charge current it is capable of. I would be leery of running 60A back-current through FETs rated at 100A forward current.



I guess the solar charger could still be hooked up to the charge port and will be turned off if the battery voltage gets too high.... but the BMS would probably not protect from the Inverter/charger over-charging.

 

[Dzl]

Does anyone know what the '50A Charge limit' on the Daly BMS means?
Does it mean if you exceed 50 amps it will damage the unit?
**OR**
Does it mean the BMS will limit the charge current to 50 Amps?
**OR**
Does it mean it will detect an error and shut off charging if it goes above 50 Amps?

@Will Prowse used a lot of Daly BMSs back before we got so many options..... I hope he might know.

I have not used the Daly either so take my perspective as conjecture as well, but I have a vague impression none of the BMS' commonly used here (Daly, Ant, JBD, Chargery, SBMS) are capable of current limiting. I believe most of the FET based BMS' advertise overcurrent protection. So my guess is option 3: detect an error and shutoff charging or maybe shutoff all current in both directions I don't know.

This is an area I would like to learn more about, what is meant by overcurrent protection, how does it work, and is it designed to protect the system on a semi-regular basis, or is more of a catastrophic failure feature.

Also, as I learned more about Victron's guidance RE: the battery protect, I'm wondering if some of that same advice could/should apply to FET based BMS as well. The two things you don't want to do with the battery protect (as far as I understand) is (1) use it bidirectionally, and (2) use it to switch large loads with capacitors on the input side of the load (most commonly an inverter). This second point is what's got me thinking, because apparently failure due to this second mode is often quite slow, so it wouldn't be easily diagnosed or identified. This is just pure speculation, from someone not knowledgeable enough about electronics to be a competent speculator, so don't read into this too much. Something to ponder though.

 

[John Frum]

I have not used the Daly either so take my perspective as conjecture as well, but I have a vague impression none of the BMS' commonly used here (Daly, Ant, JBD, Chargery, SBMS) are capable of current limiting. I believe most of the FET based BMS' advertise overcurrent protection. So my guess is option 3: detect an error and shutoff charging or maybe shutoff all current in both directions I don't know.

This is an area I would like to learn more about, what is meant by overcurrent protection, how does it work, and is it designed to protect the system on a semi-regular basis, or is more of a catastrophic failure feature.

Also, as I learned more about Victron's guidance RE: the battery protect, I'm wondering if some of that same advice could/should apply to FET based BMS as well. The two things you don't want to do with the battery protect (as far as I understand) is (1) use it bidirectionally, and (2) use it to switch large loads with capacitors on the input side of the load (most commonly an inverter). This second point is what's got me thinking, because apparently failure due to this second mode is often quite slow, so it wouldn't be easily diagnosed or identified. This is just pure speculation, from someone not knowledgeable enough about electronics to be a competent speculator, so don't read into this too much. Something to ponder though.

Over current protection is achieved by disconnect like a breaker. To reset a Daly bms you bridge b- to c- or p- I think it can also be achieved by disconnecting the balance leads

 

[BiduleOhm]

It appears that you can put a reverse current through FETs in the BMS. (That is the way some of the hybred port BMS's seem to work.) You can get away with this for lower currents but if you tried to charge through the discharge port at a high amperage, things could get dicey. Either way, the BMS is operating in an unspecified way so knowing what level of current is 'safe' is very difficult. @BiduleOhm could probably add some detail here. He seems to have a strong understanding of analog circuit design and the various components. He reacted pretty negatively when we discovered a hybrid-port BMS that worked that way. (This is similar to running current backwards through the FETs of a Victron Battery Protect that @Will Prowse did in one of his builds. The build worked but Victron was adamant that it was a fire danger and was a completely unsupported configuration of the product. Consequently, Will changed the design.)

Yes, all mosfets have a body diode who is here due to how mosfets are constructed, you can't avoid it. See here : https://electronics.stackexchange.c...tand-the-intrinsic-body-diode-inside-a-mosfet for more info

No there's nothing wrong to pass a small current through them if you need to (that's actually what APC UPSs do to charge the batteries: the body diodes of the main H bridge mosfets form a good old bridge rectifier). The problem is when you pass a higher current as the mosfet will dissipate far more power than it would for the same current in the normal direction, leading to it's destruction and potentially a fire.

Some BMSs exploit those diodes to act like a separate port BMS when they are a common port BMS (the main advantage is to be able to maintain charging in case of a low voltage disconnect event for example) and I was really surprised to see that as I know they can't possibly handle a large current for long as I had the same idea for my BMS. I ran the numbers to find a TDP in the hundreds of W while in normal operation it's designed to dissipate less than 45 W (at 300 A continuous) and it's already a challenge to dissipate that much given the other constraints I have, so a few hundreds W is out of question.

Now they are able to do it by mitigating the problem by using a lot more mofsets than necessary for the normal current direction (like 2 or 3 times more) and sensing the temperature to cut all current if it's too high. They also have the life much easier as it's for 50 to 150 A BMSs, not 300 A ones. The main concern I have with this approach is that is case of rapid current increase the thermal sensing will lag too much and the mosfets will be destroyed before it can be sensed.

In any case you can't pass as much current as in the normal direction (wild guess is half of it in the reverse direction would be the ultimate maximum you can reasonably design and I would not go that far personally, maybe 1/4 to 1/3 at most) and all current you pass will introduce a significant voltage drop (about 0.5 to 1 V for most mosfets diodes) so you'll lose some power in the process.

Also, if possible, set the inverter charger to something lower than the 60Amp charge current it is capable of. I would be leery of running 60A back-current through FETs rated at 100A forward current.

I wouldn't either, first because it's a lot of losses for nothing and most importantly because of the fire hazard.