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FAQ

Can I mount the cell boards off to the side?

NO.

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

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

Can I use external temperature sensors?

Please don't.

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?

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?

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. One such logger is the CarChip

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

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

You have two options:

• Use CurrentWays chargers, which can be connected in series (with no center tap connection to the battery pack), for up to 900 V operation

• Use Brusa chargers (or such chargers), which 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?

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 256 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.

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 BMSs 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 BMS must be configured for normally open, and grounded if limited; that way the corresponding limit outputs of the 2 BMS 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.

It 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.

Placing a connector on the comm cable

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 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?

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

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