Lithiumate™ FAQ Frequently asked questions

This page answers some of the most Frequently Asked Questions
about the Lithiumate BMS.
 
 
 
 
 
 

⇪Can I replace Lead Acid with Li-ion in a solar installation?

Yes.

However, there are 2 things you need to be aware.

• The low voltage cutoff in your inverter WILL NOT PROTECT a Li-ion battery! Li-ion batteries need cell level protection, not battery level protection. You need a BMS, and, more crucially, the BMS MUST be able to turn off the battery current, DIRECTLY! Because most inverters do not have a way to turn off the battery current, YOU have to provide a way to turn off the battery current (usually a contactor).
• A BMS controls charging and discharging separately, meaning that there have to be SEPARATE CHARGING AND DISCHARGING paths. Because you are replacing a Lead Acid battery, which has only one path for both charging and discharging, you will not be able to use Li-ion as a drop in replacement. You will instead need to create separate charging and discharging paths. You can do that with two contactors and two rectifier diodes. One diode will be in the charging direction, and in series with the contactor that controls charging. The other diode will be in the discharging direction, and in series with the contactor that controls discharging.

Please read this application note on Lead acid replacement.

⇪Is the high voltage side isolated from the low voltage side?

Yes.

There are optical isolators on the end cell boards that provide galvanic isolation. Therefore, the cell boards (up to the optical isolators) are connected to the high voltage side (the cells). Everything else is connected to the 12 V supply: the communication cables, the BMS controller, the CAN bus, the RS232 port the digital and analog inputs and outputs.

⇪Is there a fuse on the cell board?

Recent cell boards (spring 2012) have a fuse.

The fuse is not in series with the entire cell board circuit: it is only in series with the components that, if damaged, would slowly drain the cell to which the cell board is connected.

What the fuse does:

• The fuse is to prevent a damaged cell board from slowly draining its cell.

What the fuse doesn't do:

• The fuse does not prevent damage to a cell board: incorrect installation of a cell board will still damage the board
• The fuse doesn't prevent a short circuit on the cell board from shorting across a cell:
  • In case of short across the cell board, a PCB trace will fuse, not the fuse itself.
  • No single component failing in a shorted state will result in a short across the cell board
  • Only if two components would both fail in the shorted state would there be a short across the cell board
  • Or, the user could create a short across the cell board with a tool or a wire
• A cell board with a blown fuse is damaged, is not repairable, and must be discarded

All cell boards are safe: they do not cause fires, and they do not short across the cell.
This is true, whether a cell board does or does not have a fuse.

The following boards have a fuse:

• Lithiumate Lite negative end cell boards, any rev (black)
• Prismatic cell boards rev E (0.7 inch long)
  • Positive end (red)
  • Mid (green, marked 100EP031B)
  • Negative (black)
• Pouch cell boards rev C (marked 100EP009C)

The following cell boards do not fave a fuse:

• Small Cylindrical cell boards
• Dual large Cylindrical cell boards
• 1PR2500 dual prismatic cell boards

⇪Can I add fuses?

Yes, but...

Elithion discourages the addition of fuses to its BMS.

Yes, fuses on the tap lines are a good idea in a non-distributed BMS. But the Lithiumate BMS is a distributed BMS, and, as such, is inherently a safer BMS in which electronics are only exposed to 3 volts or so, not the entire pack voltage. Therefore, no fuses are necessary.

An in depth understanding of the full range of complex issues involved will reveal that added fuses:

• Do not result in protection as a superficial analysis may suggest
• May result in loss of performance and reliability
• Actually increase the chance of an unintended short circuit

Having said, that, if you absolutely must add fuses to a Lithiumate BMS, we would like to offer some guidelines

There are four locations where someone may consider adding fuses:

• In series with a cell voltage sense wire
• In series with a communication wire between adjacent cell boards
• In series with the communication harnesses from the BMS master to the positive end cell board
• In series with the communication harnesses from the negative end cell board to the BMS master

NOTE: Elithion does not support customers who place fuses in series with a cell voltage sense wire.
If you do, you are on your own, so please do not ask for tech support on the resulting issues.

Placing a fuse in series with a cell voltage sense wire will affect the voltage measurement, because of the voltage drop across the fuse during a measurement.

If the fuse resistance is greater than 25 mOhm, the voltage reading will be lower than the actual cell voltage. Typically, only fuses 4 A and higher will have such a low resistance.
This fuse must be rated for 250 mA or more, rated for DC, and, depending on the intended purpose, it should be rated either for 6 V or for the entire pack voltage.(e.g.: 300 V).

Placing a fuse in series with a communication wire between adjacent cell boards is OK and has no known side effects, other than loss of reliability and increased chance of unintended short circuits.

Placing a fuse in series with the communication harnesses from the BMS master to the positive end cell board is OK and has no known side effects.
This fuse must be rated for DC operation, and for the entire pack voltage.
For full protection, three fuses would be used, one in series with each of the two wires and one in series with the shield.

Placing a fuse in series with the communication harnesses from the negative end cell board to the BMS master may result in loss of noise immunity, because the fuses are not shielded.
This fuse must be rated for DC operation, and for the entire pack voltage.
For full protection, three fuses would be used, one in series with each of the two wires and one in series with the shield.

⇪Can I mount the cell boards off to the side?

No.

The Lithiumate is a distributed BMS: each cell board MUST be mounted directly on its cell.

Do not attempt to use it as a centralized BMS: cell boards off to the side.

Attempt to use it as a centralized BMS will result in improper operation: poor noise immunity, low accuracy, no temperature sensing.

⇪Where is the temperature sensor?

In the cell board, marked "T1".

For example, on a Pouch and on a Prismatic cell board:

⇪Can I use external temperature sensors?

No.

Some have tried, with terrible results.

The temperature sensors on the cell boards work quite well.

While it is physically possible to remove the thermistor from the board and to replace it with leads going to a thermistor mounted on the cell, the functionality of the cell board will be severely compromised:

• The thermistor acts as an antenna, picking up electrical noise, making the cell board misbehave
• The cell board measures the thermistor during a very short pulse (~1 µs), which is enough for a board-mounted sensor, but not enough to measure an external sensor, due to the additional capacitance
• The characteristics of the external thermistor may not match the ones of the on-board thermistor, resulting in reading inaccuracy

⇪Can I mount the Lithiumate on a pre-made battery module with a small BMS connector?

No.

In pre-made battery modules (such as those sold to model airplane hobbyists), there is no direct physical access to the individual cells.

In a distributed BMS, the cell boards must be physically mounted directly on the cells.

Therefore, a distributed BMS cannot be used on a pre-made battery module. A non-distributed BMS is required instead. Elithion does not make non-distributed BMS.

You may not modify a Lithiumate BMS to work as a non-distributed BMS. It will misbehave and it will not protect the pack from operating outside its safe temperature range.

⇪Does the Elithion BMS log data?

No.

There is no data logging on the BMS. For that matter, there is no data logging in any controller used in vehicles. Yes, the BMS controller does log events (just a few events) as other vehicle controllers do, but not data.

Data logging is a job best left to data loggers, which are product designed just for that purpose.

Even if a BMS controller did data logging, its data (voltage, current and temperature) would be of limited use, without the ability to correlate it with what else was going on in the vehicle at the time.

The best placement for a data logger, is on the CAN bus, where it is able to record a variety of information (e.g.: throttle position, RPM, battery status...).

Just Google "OBD II logger" to get some possible solutions.

⇪Can I split the pack in 2 and use a charger on each half?

Yes.

With a high voltage pack, it is hard to find a charger that can handle the full pack voltage.

You have two options:

• Use chargers (such as Current Ways) that can be connected in series (with no center tap connection to the battery pack), for up to 900 V operation
• Use chargers (such as Brusa) that can be connected in series but require a center tap connection to the battery pack

In the latter case, you may want to split the pack in two, and have two chargers, one for each half of the pack. But then you are faced with the problem of how arrange the BMS.

The Lithiumate BMS can only deal with one number for pack current (only one value for the SOC). Therefore: a) either you use 1 BMS, in which case the current must be exactly the same for both halves, b) or you must use 2 different BMSs.

With a Lithiumate, you can use either of these two approaches, each of which has some limitations.

The choice between 1 BMS and 2 BMSs depends on many factors:

• Is CAN used?
  • If so, number of CAN buses: 1, or more?
  • If CAN, is the charger controlled by CAN?
  • If so, does the CAN message control the CV setting?
• Is there a VCU?
  • If so, is the VCU on during charging?
• Is convenience charging the norm, or is full charging the norm?
  • If full charging is the norm, is an exact knowledge of SOC during charging required?

Note that the isolation test function and the precharge resistor sense functions in the HVFE are limited to 800 V. With packs that can reach 800 V:

• To use the isolation test, use high voltage Zener diodes between the pack and the B+ and B- inputs of the HVFE, to drop the voltage down to less than 800 V in the worst case
• To use the precharge resistor sense, you need to split the precharge resistor into two resistors in series, each of half the resistance, and let the HVFE sense the voltage across just one of them; or you can use the load current sensor to detect the end of precharge, instead of sensing the precharge resistor voltage.

1 BMS

In this approach, one BMS looks at the entire pack as a single string, and controls both chargers at the same time.

The Lithiumate can handle 255 cells, which is enough for high voltage packs. But, it can handle only one value for pack current, and it has only one output to turn a charger on and off. (Configure the BMS for a single series string, not for 2 batteries in parallel.)

One slight problem is that the top half charger could be off because the BMS told it to, because a cell in the bottom half is too full, even though the top half of the battery could still accept charge. This is not really a problem, but the user may complain that one charger is off even though its half of the pack is still not full.

A somewhat larger problem is that, with 2 chargers, the currents in the two halves of the battery are different. You can place the current sensor on one charger's output or on the other. The BMS will be able to estimate the SOC of whichever battery half has the current sensor. For the other half pack, the SOC will be off, in proportion to the difference between the output current of the two chargers. Even if the chargers were absolutely identical, they would behave differently once they go into the Constant Voltage mode, because of differences in the cells in their respective half of the battery.

So, yes, it will work, but the SOC of one of the 2 halves (the one without the current sensor) will be off.

CAN bus

The problem does not go away if the chargers report the charger current through the CAN bus: the BMS can only handle one input message with pack current data.

Another problem is raised if using the CAN bus: the value for the maximum pack voltage that the BMS reports to a CCCV charger.

If the Constant Voltage point of the chargers is set independently of any data on the CAN bus, then there is no problem.

But, if the Constant Voltage point of the chargers is set through the CAN bus, then the BMS must be configured as if the two halves of the battery were two strings in parallel (number of parallel batteries = 2); that way, the BMS calculates the correct CV point for the chargers: 1/2 the pack voltage.

That solves the problem when charging, but then you may have a problem when the load is on, because the BMS reports only 1/2 the pack voltage.

The solution involves adding some intelligence to a VCU (Vehicle Control Unit) or some such controller, to do one of two things:

• Double the value of pack voltage reported by the BMS (by saying that the units are 2 V instead of 1 V), or
• Switch the configuration of the BMS, through the CAN bus, from 2 batteries in parallel to 1 (switching back when the ignition goes off can be a challenge)

As you can see, the first solution is much easier.

1 BMS and rectifiers

Here is a clever circuit to split a pack: parallel charging, series discharging.

When the AC is available, the charger is on, and a contactor opens the series connection between the half packs.
Rectifier diodes are forward biased, effectively connecting the two half packs in parallel, and the charger charges both half-packs.
The BMS needs to be told that the half-packs are in parallel, so that it can report the correct pack voltage.

When the AC is gone, the contactor closes, and the packs are connected in series.
The rectifier diodes are reverse biased, disconnecting the charger from the half-packs.
The BMS needs to be told that the half-packs are in series, so that it can report the correct pack voltage.

To our knowledge, the Lithiumate BMS is the only BMS that can handle strings in parallel, and specifically the only BMS that can be switched on the fly between 1 series string and 2 strings in parallel.

2 BMSs

In this approach, 2 BMS are used, one for each half of the battery.

Each BMS controls its own charger; therefore, the chargers are used more optimally. Also, each charger has its own current sensor; therefore, the SOC of each half is computed correctly.

If each BMS controls its charger through the CAN bus, and there is no CAN bus to the load, then you can use two separate CAN buses, one for each charger. To control the load, the limit outputs of the 2 BMSs must be configured for normally open, and grounded if limited; that way the corresponding limit outputs of the 2 BMSs can be paralleled (LLIM to LLIM, HLIM to HLIM), and sent to the load.

If a common CAN bus is used, then one of the BMSs must be configured so that the IDs of its messages do not conflict with the messages from the unmodified BMS; each charger must be configured to accept messages from its own BMS.

If that common CAN bus is used to report to the system (say, a vehicle) the status of the battery, then a VCU (Vehicle Control Unit) is required; the VCU must be programmed to receive messages form both BMSs, each with its own set of IDs; the VCU must intelligently decide what the battery SOC is, given the SOC reported by each BMS.

Note that you cannot use two HVFEs simultaneously to do an isolation test, as they will interfere with each other.

⇪Can I break the comm cable with a connector?

Yes.

The option of breaking the comm cables through a set of connectors is not something that we designed into the product.

Therefore, we are not able to recommend a specific connector for the job.

Should you decided to split the comm cable with a connector, do follow these guidelines:

• Use a 5-way connector for each bank, to carry through all 5 wires (one of which is the shield)
• Alternatively, use 4-way shielded connectors, but make sure you do not let the shield touch the chassis, as that would result in loss of noise immunity
• Avoid bulkhead shielded connectors that are mounted to the metal chassis, as that would result in loss of noise immunity
  • In any case, absolutely do not connect the shield of the comm cable to the shield of a bulkhead mounted shielded connector
• Running multiple banks through the same multi-way connector (such as 10-way for 2 banks, 15-way for 3 banks) is not recommended, due to cross talk
  • In any case, absolutely do not connect the shields of the comm cables together: each shield must remain isolated from the other shields
• Do not expose more than 3/4" (2 cm) of unshielded wire on either side of the connector.

⇪Can I use a different current sensor?

Yes.

While you are certainly free to use a different current sensor, other than the ones we sell, it is really your responsibility to assure that that sensor is compatible with your application and with the BMS controller.

• The BMS controller provides 2 supplies:
  • Ext Curr connector (black): +/-15 V (up to 30 mA)
  • Control connector (white): +5 V (up to 50 mA)
• The BMS controller has 2 analog inputs for a current sensor:
  • Ext Curr connector (black): accepts a +/-5 V signal
  • Control connector (white): accepts a 0 to 5 V signal
• The BMS controller software can at most be set for a gain of 255 A/V, therefore the maximum current is 1275 A

⇪Can the BMS handle 2000 A?

Yes, though with some limitations:

• The biggest current sensor we offer is rated for 600 A nominally, but is able to report as much as 900 A.
• The BMS can be configured for up to 637 A (bidirectional) or 1275 A (unidirectional).

We offer workarounds, based on the application:

1) For applications that have continuous currents up to 600 A, and peaks up to 2000 A (e.g.: a race car):

• Use a 600 A sensor and split the current in half or 1/4 with a current splitter, or
• Use a 600 A sensor and live with the fact that the SOC will be slightly off because the BMS saw 900 A instead of 2000 A for 10 seconds or so during your acceleration, or
• Use a 600 A sensor and come to the realization that, even though your motor driver is rated for 2000 A, in reality the battery current is almost always lower than the motor current, and so the battery will never see 2000 A, or
• Use a 600 A sensor and come to the realization that your particular battery may not possibly be able to put out 2000 A, or
• Find a different current sensor, one that can handle 2000 A, and that is compatible with the Lithiumate Pro, or

2) For applications that have continuous currents of 2000 A.

• Enable the BMS to sense a higher current in one of these 2 ways:
  • Find a different current sensor, one that can handle 2000 A, and that is compatible with the Lithiumate Pro, or
  • Use a 600 A sensor and split the current in half or 1/4 with a current splitter
• Configure the BMS for 1/4 the actual current.
• Configure the BMS for 1/4 the actual capacity.

For example, if the battery is 1000 Ah, and the current is 2000 A, configure the BMS for 250 Ah to report 500 A instead of 2000 A.
That way, the SOC will be reported correctly.

⇪Are the boards conformally coated?

Some.

• The prismatic, small cylindrical and large cylindrical cell boards are.
• The pouch cell boards are not.
• The controllers (BMS master and HVFE) are not.

The pouch and small cylindrical cell boards are soldered by the user; conformal coating would get in the way of soldering.

The controllers include connectors that are not compatible with conformal coating: the coating would wick up onto the contact area and cause problems.

In any case, our experience of systems that were inappropriately used in harsh environments is that the electronic boards have no problem, while the connectors can become badly oxidized. Conformal coating may give the user the false impression that these products may be used in harsh environments, when in reality, they cannot.

The user must assure that the entire battery, including the BMS, be used in a protected environment.

For marine applications, and other harsh environment applications, please contact us to discuss our sealed version of the product, available only in large volumes to industrial manufacturers.

⇪Can I use 1 BMS to manage 2 batteries?

No.

1 BMS = 1 current sensor = 1 SOC value = 1 set of on-off control lines

With two batteries, you have 2 currents, 2 SOC values, and each one needs to be turned on and off independently of the other.

Therefore, 2 batteries = 2 BMSs.

(To manage a small, 12 V, Li-ion battery, use a PCM - analog protector.)

⇪Can I use 1 BMS to manage more than 1 charger?

In general, yes:

• Yes: Dumb chargers (no CAN bus) (e.g.: Manzanita Micro, ElCon w/o CAN...)
• Yes: Smart chargers (with CAN bus), where 1 charger is the master (e.g.: CurrentWays, Brusa with Booster)
• Depends: Smart chargers (with CAN bus), where all charger are peers (e.g.: Eltek, ElCon w/CAN, Brusa w/o booster)
  • Yes: if used as dumb chargers (on/off control only; use a current sensor to read the total charging current)
  • Not directly: it you want the BMS to control the charging current through the CAN bus and receceive from the chargers the total actual charging current

There are multiple problems when using multiple smart chargers, where no one charger is the master:

• The BMS does not know how many chargers there are; so, if it says (10 A max), each charger will put out 10 A (for a total of, say, 100 A if there are 10 chargers)
• If all the chargers talk on the same CAN ID, the BMS knows that some chargers are putting out, say 10 A, some 10.2 A, some 10.5 A, but it doesn't know if is one charger whose current is changing rapidly, or multiple chargers each with its own current; and, in the latter case, not knowing how many chargers there are, the BMS doesn't know how to add all the values it receives
• If each charger talks on its own CAN ID, as the BMS is only able to listen to one CAN ID, it misses all the others

So, for smart chargers where no one charger is the master, you need a specialized controller that acts as the master. That way, the BMS only has to talk to one device, and listed to one device: that controller.

To date, no charger manufacturer offers that product; specifically, Eltek told us that they do not intend to offer such product.

Therefore, you will need to design your own solution (using a CAN bus gateway), or you can hire Elithion to design one for you.

⇪Does the BMS use CANopen?

No.

CANopen is a closed standard (ironically), and having a product certified is an expensive process. Also, CANopen adds a significant layer of complexity to the communications on the CAN bus, making it more busy than it needs to be.

Therefore, Elithion products are not CANopen compatible, at least not directly.

However, Gateways that convert a standard CAN bus communication to CANopen are readily available on the market.

⇪Does the BMS interface to motor drivers through the CAN bus?

Some.

From the point of view of control mothod, there are 3 types of motor drivers today.

1. No support for CAN bus (e.g.: Kelly)
2. May be controlled by CAN bus, through there are no mesages that allow for direct interface to a BMS (e.g.: UQM)
3. May be controlled by CAN bus, including mesages that allow for direct interface to a BMS (e.g.: MES-DEA)

The Lithiumate BMSs (Lite and Pro) are compatible with all motor drivers through simple wire control (# 1through 3 above)

The Lithiumate Pro BMS is directly compatible with all motor drivers that include mesages that allow for direct interface to a BMS (# 3 above)

The Lithiumate Pro BMS is indirectly compatible with all motor drivers that do not include mesages that allow for direct interface to a BMS (# 2 above); this is one through a central controller (usch as a VCU - Vehicle Control Unit).
The central controller must be programmed for the specific application to interfcace with all CAN enabled devices in the application, including the motor driver and the BMS.
The central controller is the brain that, given the input data, will tell the motor driver how to control the motor.
For example, given the throttle position, the present speed and the maximum battery current (reported by the BMS), a VCU will feed those data to a servo loop, whose output defines the desired motor speed and torque.
The effort required to program such a central controller is extensive; it is impraqctical to do so for just one unit, or just a few units.
Therefore, unless a product is intended to be produced in high volume, it is much better to:

• Forgo CAN control (use wire control), or
• Select a motor driver that does include mesages that allow for direct interface to a BMS

This list of motor drivers shows which ones have CAN bus support, and, of those, which ones are directly compatible with a BMS in general, and therefore compatible with the Elithion Lithiumate Pro BMS.