Charge Daly BMS through discharge port, Still balances?

[rg12]

I've got a Daly 16S 60A with separate discharge port and would like to use the discharge port for charging and don't mind not having a max charge current limit.
My concern is about the balance if it will still balance like it charges through the separate charge when charged from the discharge port.

 

[amberwolf]

You must check with the specific BMS manual or manufacturer to be sure, but generally with "cheap" balancing BMS designs the balancers simply always "work" whenever cells are above whatever their balance voltage limit is (whether it's programmable or not).

However, you have ZERO protection against overcharging your cells or battery when charging thru the discharge port, because the system physically cannot prevent current flow back thru the discharge FETs, whether they are on or off.

That's why you must use a BMS that has only one port for both functions, if you want to do both functions thru one port, if you care whether a pack is ever overcharged (or overdischarged in the case of doing the opposite port misuse).

 

[rg12]

You must check with the specific BMS manual or manufacturer to be sure, but generally with "cheap" balancing BMS designs the balancers simply always "work" whenever cells are above whatever their balance voltage limit is (whether it's programmable or not).

However, you have ZERO protection against overcharging your cells or battery when charging thru the discharge port, because the system physically cannot prevent current flow back thru the discharge FETs, whether they are on or off.

That's why you must use a BMS that has only one port for both functions, if you want to do both functions thru one port, if you care whether a pack is ever overcharged (or overdischarged in the case of doing the opposite port misuse).

All I know is that it will have the current limit of the discharge for the charge but why wouldn't it protect against over voltage?
It just shuts off current through the mosfets, it's not that I charge bypassing the bms and there are no mosfets in line anymore to turn off the negative wire.

 

[fechter]

The discharge FETs can't stop the charging current if a cell goes over voltage. There is an intrinsic diode in the FET that will still allow current to flow in the reverse direction even if the BMS is tripped. The balancing function will most likely still work.

They do make "single port" style BMS units that charge and discharge through the same pair of wires. One of these will work for charging through the discharge wires.

 

[SirWilliam]

I note that Daly are marketing 48 Volt BMS`s some marked 14S and some 13S
Which type should I use for a 13 S/5P Panasonic 3400ma battery
Is this 14S 48 Volt type so that the user use a wider range of voltage during the discharge curve??
Bill Clark

 

[rg12]

The discharge FETs can't stop the charging current if a cell goes over voltage. There is an intrinsic diode in the FET that will still allow current to flow in the reverse direction even if the BMS is tripped. The balancing function will most likely still work.

They do make "single port" style BMS units that charge and discharge through the same pair of wires. One of these will work for charging through the discharge wires.

Thanks mate

 

[john61ct]

I note that Daly are marketing 48 Volt BMS`s some marked 14S and some 13S
Which type should I use for a 13 S/5P Panasonic 3400ma battery

Standard 48V packs for LI chemistries @ nominal 3.6-3.7V


are 13S charging at 52-54.6V

actually a bit too low compared to lead and LFP chemistries, @3.6Vpc is 46.8

but standard for COTS eBikes

14s are nominally 52V packs, charging between 56-58.8V

em3ev calls that a 50V, but I've seen them labeled 56V too

a bit more power for torque, and also little faster top speed than 48V

No "wider range", in fact going higher voltage often results in shorter range, using more energy per mile.

Obviously use a 13S BMS for a 13S battery.

 

[amberwolf]

All I know is that it will have the current limit of the discharge for the charge

No, it won't.

The discharge fets cannot shut off charge current.

They are just always-on diodes to charging current flowing thru them.

The only way to shut off charge current, for ANY reason (overcurrent, overvoltage, overheating, etc), is to charge thru the CHARGE fets.

Charging thru the DISCHARGE fets is almost exactly like connecting the charger directly to the cells, without a BMS at all (except that it will be generating heat within the discharge fets, because they're not intended to be used this way).

 

[amberwolf]

The balancing function will most likely still work.

It will "work" only in that it will drain cells that go above the balancing voltage the BMS is designed or programmed to do, *if* the charge current at that point is *lower* than what the balancers can bypass around those cells, *or* the charger is disconnected or turned off.

Otherwise, those cells will continue to charge, and if they're already at their max voltage, they'll be overcharging.


It will NOT work in that it cannot shut off charging current, so any cells that reach that point are already "full", yet will continue to be overcharged while the charger keeps charging all the other cells, if the charge current at that point is above what the balancers can bypass around the already full cells.


So if you have some really low cells and some really high cells, and use the discharge port for a charge port, and the charge current remains above the balancer bypass ability long enough, you may overcharge those already-full cells enough to seriously damage them, or even cause a fire, because there is nothing to shut the charge current off.

 

[amberwolf]

It just shuts off current through the mosfets,

The point is that no, it cannot shut off current thru the fets, unless you use the right port for the purpose.

it's not that I charge bypassing the bms and there are no mosfets in line anymore to turn off the negative wire.

Yes, you *are* bypassing the BMS by doing this, and there indeed are NO mosfets that can turn off any wires, unless you use the right port for the purpose.


Don't use the discharge port for charging.

Don't use the charge port for discharging.

If you do, you have wired around the BMS and it can't protect your pack.

 

[john61ct]

There are BMS where you can switch configuration between common port and separate.

 

[SirWilliam]

I note that Daly are marketing 48 Volt BMS`s some marked 14S and some 13S
Which type should I use for a 13 S/5P Panasonic 3400ma battery

Standard 48V packs for LI chemistries @ nominal 3.6-3.7V


are 13S charging at 52-54.6V

actually a bit too low compared to lead and LFP chemistries, @3.6Vpc is 46.8

but standard for COTS eBikes

14s are nominally 52V packs, charging between 56-58.8V

em3ev calls that a 50V, but I've seen them labeled 56V too

a bit more power for torque, and also little faster top speed than 48V

No "wider range", in fact going higher voltage often results in shorter range, using more energy per mile.

Obviously use a 13S BMS for a 13S battery.

So to get more capacity would I be better going for an extra parallel row of cells (i.e. from 5P to 6P)
Do you think that 58.6 volts would damage a 48 volt controller
Bill C

 

[fechter]

So to get more capacity would I be better going for an extra parallel row of cells (i.e. from 5P to 6P)
Do you think that 58.6 volts would damage a 48 volt controller
Bill C

No damage, but the low voltage cutoff might not be at the desired setting. Often times this can be easily adjusted.

 

[john61ct]

So to get more capacity would I be better going for an extra parallel row of cells (i.e. from 5P to 6P)

Yes more Ah capacity is **always** better 8-D

Subject to budget issues, space available and the desire for lower weight

 

[docw009]

Don't charge thru the discharge port. Accidents and user error are free to happen when you bypass a safety net. .

One time, I accidentally connected a 48V charger to the output port of a 36V pack. Destroyed the pack. I never charge overnight, otherwise could have been bad. Caught it before the cells popped off, but it sure was hot.

 

[rg12]

All I know is that it will have the current limit of the discharge for the charge

No, it won't.

The discharge fets cannot shut off charge current.

They are just always-on diodes to charging current flowing thru them.

The only way to shut off charge current, for ANY reason (overcurrent, overvoltage, overheating, etc), is to charge thru the CHARGE fets.

Charging thru the DISCHARGE fets is almost exactly like connecting the charger directly to the cells, without a BMS at all (except that it will be generating heat within the discharge fets, because they're not intended to be used this way).

Don't forget that regen does that all the time...

 

[amberwolf]

Charging thru the DISCHARGE fets is almost exactly like connecting the charger directly to the cells, without a BMS at all (except that it will be generating heat within the discharge fets, because they're not intended to be used this way).

Don't forget that regen does that all the time...

No, in almost all use-cases of regen, it only does it for a few seconds here and there, when the pack is already discharged to some degree (unless you begin your trip at the top of a hill and start out having just charged up to full).

And the regen case only applies if you have a BMS with separate ports; if it has a single port for both, then the BMS can protect either way.

 

[SirWilliam]

I am a bit new to this subject.
When the contributors are taking about charge and discharge ports how does this work with say these Daly BMS`s that have only a B- & a P- connections. As these BMS`s do not have a C- connection all charge and discharge takes place both ways in the B-/P- Wires.
Is this OK?
Regards
Bill C

 

[fechter]

I am a bit new to this subject.
When the contributors are taking about charge and discharge ports how does this work with say these Daly BMS`s that have only a B- & a P- connections. As these BMS`s do not have a C- connection all charge and discharge takes place both ways in the B-/P- Wires.
Is this OK?
Regards
Bill C

BMS boards come in both styles. If there is only a B- and P-, I call it a single port. If there is a separate C-, then I call it a two port.
Both styles work OK. The dual port style only passes the discharge current through one bank of FETs. The single port style passes the current through two banks of FETs, so will have roughly twice as much heating for a given current. If the board is adequately sized and installed, heating won't be a limiting factor.