# Battery Schematic



## jskwigy (Oct 6, 2009)

For the first part of our senior design project my goal next weekend is to assemble and test the capacitance of our 72 Thundersky TS-LCP 50AHA batteries. I will be putting our BRUSA NLG503 charger in parallel with the circuit as this makes the most sense to me. Provided below is the drawing of my idea.

Input would be greatly appreciated.










J. Albrektsen


----------



## icec0o1 (Sep 3, 2009)

If you swap the return and feed to the outer terminals, than you won't need to use the two longer cables. Nope, wait that doesn't work 

Okay, if you do a 9 x 8 grid, then you won't have to use longer cables. You need an odd number of cells for one of the dimentions.


----------



## Qer (May 7, 2008)

That way you don't need the long interconnect wires, get the two terminals close to each other and (hopefully) limit the interference which might affect radio reception, PakTrakr or whatever. It's probably possible to try to cancel out noise even more by work more with the internal linking of the pack, twisting the cables etc.

Typically you want to run all high current as close to each other as possible so they cancel out the electro magnetic noise as much as possible.


----------



## zaxxon (Jul 11, 2009)

How are you planning to discharge and measure the batteries to check their capacity under load? 

Also, if your cells do not have a battery balancing circuit installed, you should measure each one to make sure they are within +/-0.1 volts before charging and discharging them all in series. To get them to the same voltage you could parallel all the batteries with a 1 ohm resistor in series which each positive terminal to limit the current until the voltages are the same.


----------



## IamIan (Mar 29, 2009)

jskwigy said:


> For the first part of our senior design project my goal next weekend is to assemble and test the capacitance of our 72 Thundersky TS-LCP 50AHA batteries.





zaxxon said:


> How are you planning to discharge and measure the batteries to check their capacity under load?


I thought he was trying to test the capacitance ... not the capacity?
They are not the same thing.


----------



## jskwigy (Oct 6, 2009)

I do not have a battery balancing system for our setup. I had read Jack Rickard's blog and he had stated that balancing wasn't too much of an issue and not worth the spaghetti nightmare of the wiring. Am I wrong to follow this advice? If I initially balance all of the batteries and then treat them as a single device I would think that they should maintain somewhat identical charges.

The BRUSA charger will monitor the total voltage of the package and cease to charge at 300(V), 72*4.2(V). I planned to create a resistive DL and a DMM to discharge the batteries individually so that they will all be near 4.0(V) or so.I do not have a battery balancing system for our setup. I had read Jack Rickard's blog and he had stated that balancing wasn't too much of an issue and not worth the spaghetti nightmare of the wiring. Am I wrong to follow this advice? If I initially balance all of the batteries and then treat them as a single device I would think that they should maintain somewhat identical charges.

And I meant capacitance, I want to make sure that these batteries which have sat in a warehouse for over 2 years will charge, hold a charge, and discharge at the 2% a month rate as advertised. Like I said they have never been used and are brand new in their crate.


----------



## IamIan (Mar 29, 2009)

jskwigy said:


> And I meant capacitance, I want to make sure that these batteries which have sat in a warehouse for over 2 years will charge, hold a charge, and discharge at the 2% a month rate as advertised. Like I said they have never been used and are brand new in their crate.


???

Capacitance is a property of capacitors ... and most batteries have some degree of this as well... but the batteries capacitance which is electro-static ... is not the same as the batteries electro-chemical ability to take a charge , hold a charge , and discharge it.

When most people refer to charging and discharging a battery to test it counting the self discharge rate ... or determining the amount of Ah that the battery will dish out from a full charge ... this is referring to capacity ... not capacitance.

This is not the say that capacitance can not act as an indicator to effects and behavior of a battery ... but capacitance which is electro-static ... is not the same as the electro-chemical capacity of the battery to take, hold, and discharge current and or energy.

I mentioned this because if this is part of a project you are doing for a class or a grade... you could loose points for using terms incorrectly.

yes capacitors store and hold energy also ... but they do it differently than batteries do... capacitors store the energy electro-statically ... like a static electric charge ... batteries instead store the vast majority of their energy electro-chemically ... they convert the electro-static energy supplied to them into chemical energy during charging and then convert it back from electro-chemical energy to electro-static energy during discharging ... the capacitor generally does not do the electro-chemical energy conversion step.

Capacitance is measured in Farads ... capacity is often measured in Ah, but is occasionally also measured in Wh.

I hope it goes well for you.


----------



## jskwigy (Oct 6, 2009)

I appreciate the clarification! I understood that capacitance is the value of energy stored in a capacitor and measured in Farads. From circuit classes I knew that batteries act pretty much like a capacitor. Granted my focus at school is in RF theory and antenna design. My group took on this project because it seemed fun and will created something more than a small PCB to look at and go "Ohhh wow! What is it again?". RF is sort of an invisible science.

With my return and feed lines going to my drive/converter, MES-DEA TIM 600, does this design look good? I do not think that the batteries will be going into the vehicle in a conventional way as storage space is extremely limited. I think I will have to have two separate battery locations all connected in series of course.

As far as EM properties I will probably use shielded cable for the links between battery locations. I hope that this will ground out any magnetic field generated by the current traveling along the lines.


----------



## Tesseract (Sep 27, 2008)

jskwigy said:


> ...
> As far as EM properties I will probably use shielded cable for the links between battery locations. I hope that this will ground out any magnetic field generated by the current traveling along the lines.


Wrong type of shielding... EMI from the battery cables comes from rectangular pulses of current being drawn by the motor controller, so you need to worry about the H-field (since you are a student, quiz time: what "shielding" method is used to suppress radiation in the H-field?).

On the motor side of the controller the opposite problem exists: the voltage is rectangular but the current is smoothed out (integrated) by the motor's winding inductance (whether that winding be the field of a DC motor or the phase legs of an induction motor). Thus, noise from the motor cables is predominantly E-field.


----------



## IamIan (Mar 29, 2009)

jskwigy said:


> I appreciate the clarification! I understood that capacitance is the value of energy stored in a capacitor and measured in Farads. From circuit classes I knew that batteries act pretty much like a capacitor.


Your welcome... 

Just one minor correction.

Farads are not a measure of energy stored.
They measure capacitance which also requires you to know the voltage in order to determine the amount of stored energy... or the potential voltage in order to determine the potential energy storage.

Kind of like ... if you just knew a Battery held 100Ah that would not give you enough information to determine how much energy in Wh that battery potentially had... if it was a NiMH cell at a nominal 1.2V it would be very different from a Li Cell at a nominal 3.6V.

It would be possible to try to use a measured Farad amount in order to extrapolate the batteries potential Ah capacity ... but I think it would be much simpler to just directly measure the Ah or Wh of capacity during a discharge cycle.

Best of luck ... tell us how it turns out when you'll all done.


----------



## jskwigy (Oct 6, 2009)

I believe that a Gaussian Cage would protect from an H-field... but that means that I would be shielding my components and not my cables. If this is so how important is this? My equipment, converter/motor/accessories, will be grounded and have a metal frame. Do I need to place a metal shield around components? In most designs I have never seen people go to that extent. I figured just go with a steel braided copper cable to and from the battery components. Of course the steel braids would be grounded to the chassis.

Call me out if I'm wrong here. My emag book is at home and I am currently at work.


----------



## zaxxon (Jul 11, 2009)

jskwigy said:


> I do not have a battery balancing system for our setup. I had read Jack Rickard's blog and he had stated that balancing wasn't too much of an issue and not worth the spaghetti nightmare of the wiring. Am I wrong to follow this advice? If I initially balance all of the batteries and then treat them as a single device I would think that they should maintain somewhat identical charges.
> 
> The BRUSA charger will monitor the total voltage of the package and cease to charge at 300(V), 72*4.2(V). I planned to create a resistive DL and a DMM to discharge the batteries individually so that they will all be near 4.0(V) or so.I do not have a battery balancing system for our setup. I had read Jack Rickard's blog and he had stated that balancing wasn't too much of an issue and not worth the spaghetti nightmare of the wiring. Am I wrong to follow this advice? If I initially balance all of the batteries and then treat them as a single device I would think that they should maintain somewhat identical charges.
> 
> And I meant capacitance, I want to make sure that these batteries which have sat in a warehouse for over 2 years will charge, hold a charge, and discharge at the 2% a month rate as advertised. Like I said they have never been used and are brand new in their crate.


Sorry, I did not know the history on the Batteries. I was only trying to make sure you made sure the batteries were at the same voltage before you start discharging and charging the batteries. You are correct, if the batteries are from the same build lot, and have had the same history they will track very well without the use of a balancing circuit. Overtime and several charges and discharges the small difference will start to accumulate and you will need to rebalance them.


----------



## Tesseract (Sep 27, 2008)

jskwigy said:


> I believe that a Gaussian Cage would protect from an H-field...


You are likely thinking of a Faraday Cage, which would work to a large extent, but it's not exactly practical as you correctly identified.

Practically speaking, _shielding_ H-fields is not practical. They are magnetic fields and therefore only magnetic materials with extremely high permeability (or which are sufficiently thick) can block them (e.g. - Mu metal... aka, snake oil, in my opinion).

However, it is eminently practical to suppress the production of H-fields in the first place, and that is by following a very important rule for both power conversion and RF: make sure the source and return conductors are as close to each other as possible. Even better is to twist them together (if it's good enough technique for 100MHz ethernet cables - which use _unshielded _twisted pair - then it's good enough for a lot of other applications).

There is a thread on here with an excellent illustration of just how dramatic a reduction in radiated noise can be obtained by merely twisting the battery cables together in the vicinity of the controller.

Anyway, keep this in mind: changing currents radiate H-field (magnetic) noise; changing voltages radiate E-field noise.


----------



## Grant_NZ (May 28, 2008)

Would twisting the cables together generate heat under load?


----------



## Qer (May 7, 2008)

Grant_NZ said:


> Would twisting the cables together generate heat under load?


No. Heat is generated by current through resistance and the resistance in the cable is defined by the copper area of the cable. See the column for resistance in this table:

http://en.wikipedia.org/wiki/American_wire_gauge#Table_of_AWG_wire_sizes

Of course, if you twist them very hard so the cables have to be longer to reach the same distance then resistance goes up and thus they produce more heat, but don't twist them that hard...


----------

