06 October, 2016

Types of Batterie Management Systems (BMS); building new batteries for our equipment

Complementing the already abundant information on this blog about batteries, recycling and repair, and BMS, I will analyze the types of BMS and qualities that we can find among Chinese BMS. The main reason for the short life of batteries any type is often their poor maintenance ; either because they remain flat or that are downloaded more than convenient (both lead as Li-ion do not tolerate discharges well below a certain level). To protect the batteries (particularly lithium dangerous if overloaded or short -circuited), the " battery Management Systems " or BMS come into play to good use and long battery life.

How to Choose the BMS we need

Before going into detail compare loading controls, beginners in this world often wonder what control they need for battery want to ride . I'll try to explain their concepts, but more to inform you that you may be experience with this issue. The BMS is linked to the battery ; the type of technology, discharge rate, number of cells is what we need to know before you even buy anything. Moreover , we have well -planned battery according to the demand of the apparatus in question before you even ask for the material. Imagine you have a baby carriage powered by lead - acid battery. If you have two 6V batteries in series, needs a total of 12V, and looking at the consumer (in this case is the motor is 100W, and what most consumed) then we will need to mount a battery that can deliver at least 8AH (100/12). If we take a battery of Lico from those used in laptops (Lithium ion and cobalt) we need at least 3 batteries in each cell (as they have 1C discharge capacity, in this case around 2,5Ah each), with 3 - cell 3.7V nominal (voltages between 9 and 12.6), which 2,6Ah batteries 9 each are covered. The BMS in this case will have to be 3S (3 cells in series) and 8A minimum (recommended 10A or more so there are no intermissions to cut the flow of current in grubbed more motor consumption) and LiCo or LiPo (they are often grouped under the name Li-ion, erroneously because of Li-ion there . many different) chemical I hope it now be a little clearer ...: P

BMS for lead batteries

A good control system balance between cells is always recommended, since no battery is factory exactly the same, always have some difference (internal resistance, capacity), but in systems of lead batteries sometimes unfeasible by high currents they handle, the resulting economic batteries, and overload tolerance, although there are balanced systems that lengthen its duration twice like this, highly recommended in large packs of accumulation of solar energy:

Balancer 12V (4x6V balancing a pack in cells 2S)
These balancers have poser consumption in vacuum up to 50mA (depending on model) because they are constantly matching, so it is only recommended for batteries that are recharged often (accumulation of solar energy and often used equipment). To this self - discharge of between 4 and 10% per month of this type of battery adds.

BMS for Lithium ion batteries

There are the controls sale Chinese cargo with very economic balancing, but we must be careful that simply protects the battery against overload / over - discharge, which must be avoided, because in a few cycles ended are crippling one of the cells. By testee example the following BMS 8S to LiFePo to put on my electric bike , fully discharging one of the cells, and load stopped when any of the cells reached the maximum, without actually loading of all the emptier. If we examine, we do not have any microcontroller , simply voltage control cascade stops loading or unloading if any cell voltage exceeds a predetermined level . And why in the page indicates that YES balances , and 70mA, which is not true:

This type of BMS only serve to protect the batteries in the charge / discharge

The following however, properly balanced , thanks to its microcontrollers, and can deliver up to 10A without problem (15 or 20A with proper ventilation). 
The technical details indicated balancing with a current of up to 70mA, but I doubt pass 30mA :

You have to pay attention to where the cables are placed rolling.

Example BMS wiring (Ebikeschool.com)

I have found little LiFePo balancers offer, as this technology is rarely used in batteries, despite its incredible qualities. The same manufacturer, they also have to  LiFePo 10S and 60A discharge current .
So, in summary, uid of BMS without central microcontroller .

Preparing a 12V battery for Sai and strollers

In this case, I took the remaining me to place on the old UPS originally employed two 6V batteries lead / gel placed in series (and ANR26650 / A1 batteries was using with old car batteries ), but well might be other uses as even a car or motorcycle starting large displacement, as protector 300A battery can deliverinstant to 12V (there are people using this system for ultralight by weight):

Protector cell battery without rolling
By delivering 13,3V end in recharging, the 4 packs of 2 batteries in series (4S2P) stay loaded in a healthy 3,32V each , representing a 90% load capacity, and not keep 100% lengthen their longevity:

Thus weighs less and has the same capacity, a very useful UPS to avoid losing parts in the 3D printer in case the lights go :)

As with the BMS, we must be careful when choosing the type of battery, since each chemical Li-ion makes them more suitable for some projects than others , but any battery can be used for any project as long as is dimensioned so not enough to overcome the load currents / recommended by the manufacturer for each battery discharge.

In this case, he needed the UPS to the 3D printer, which comes to consume 60W / hour maximum(no warm bed), so that walking cutlery and considering efficiency inverter UPS is 85% approx I need that the battery can deliver me 80W / h.
These ANR26650A LiFePO already have almost 10 years, but still retain a capacity between 1885 and 2000 mAh each, although the internal resistance has tripled degradation chemistry over the years.
The calculation passing amperes (W = V * A) is 80W / 12V = 6,66Ah

Types of Chemical Li-Ion

General summary properties of the most used batteries

I used LiFePO (iron phosphate) because its spectrum voltages between charged and discharged to 3.4V 2,9V varies, so with four serial and have required 12-13V . Moreover accept quick reloads more than 2C without damage very well (although I have not checked what amps gives the UPS to recharge), without forgetting that they can give quietly to 5C download the state they are (10A / h for holding current) so could suffice one in each cell, although in that case we would only have 2000 mAh capacity (with a consumption of 70W we would last 70 / 12V = 5,83A in an hour, with 2000 mAh would be 2000 * 60/5830 = 20 , 58 minutes).
Do not confuse the current that is capable of delivering a type of Li-ion battery with capacity.The current is usually indicated on C's that is the multiplier maximum intensity (value for loading and one for unloading) ; a higher C (LiPo can reach 50C in download but not more than 0,5-1C in download) can deliver more power without damage. I talked about it more widely when I made the first bike battery .

Welding the BMS

To connect the BMS I connect the main battery cables first; positive and negative , which usually come indicated with B + (swinging) and B- , and then I'm connecting one to one wire roll, starting with the positive or negative side, and going in order, with very careful not to mistake of polarity or we can load the BMS. 
I usually play the BMS to see if any of the integrated heated , if heated much is a sign that something is not right since; then we have to drop everything quickly and review point by point.
The battery positive goes to positive motor / controller and charger positive in this case (image: Endless Sphere)

Connections vary BMS, and sometimes does not come clear or marks integrated or schemeprovided by the manufacturer laying cables swinging (sometimes even there) then you can find out connecting major battery (B + and B-) and measuring the voltage that there is in the cables; I indicate to which position corresponds (for example if the first da + 4.2V is a BMS LiPo / LiCo that cable and go into the first cell from the positive.

After everything is connected properly, if the BMS is OK (to me more than once has not worked for me some, because some vendors send them without testing), will be able to check that gives you the desired voltage at the P + connectors and P- that This is where a rule is loaded and unloaded and may use any charger with a tolerance between the total voltage of + 5V pack as the BMS is responsible for regulating the load and voltage and stop when fully charged.

In the near future I will make a video explaining when integrating the BMS on the bike (previously used by an external iCharger 1010+).

If you have any doubt, please coment!

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