I did this type of battery shunt test a little bit different over 50 years ago when I working in a military battery shop. I apply this method to every battery pack I had in my EV,s. We use a amp meter instead of a volt meter. We connect a amp meter shunting a mechanical fasten battery link to the two posts that the link was connecting to.
Making up a new battery pack, we first torque all the link connections to the same torque reading. Turn on the battery charger and set it for a known ampere. We check the amp reading of each link and find the highest ampere reading of one link. Then we re-torque all the other battery connections until the amp meter reads the same as the highest reading. Run a load on the batteries with a load bank, or in a EV, just run the EV for about 5 miles. Do the shunt test again which in my EV only takes less than 15 minutes. It is normal to find one battery connection at about 5 inch lbs less than the initial torque of 75 in.lbs in my batteries. I than apply a thick coating of petroleum jelly to the link connection all the way down to the battery surface. The batteries are enclosed in a epoxy seal battery box that has incoming filter air drawn in with a acid proof exhaust fan. In about a month I will be getting three Nissen Leaf batteries which I will reconnect for 180 ah at 210V nominal. It is recommend to use the battery in the 3.65V - 4.15V per cell range. Do not charge over 4.2V per cell. The pictures that they sent me looks like the battery links are copper which I assume the battery load terminals are copper too. I am going to have to remove them so I can parallel three modules in parallel and series 81 of these parallel modules in series. I was planning to buff the copper bars with my metal bench mount buffer with a new buffer wheel, because the other ones had compound infuse into for other metals. After you polish or clean any links, it is best to wear throw away latex gloves, to keep the finger print oil off polish metal. I will then apply the petroleum jelly over these bars and connections. The weight of my EV which is now at 7020 lbs will weigh 5500 lbs which was about the original weight of the vehicle. My 1st gear overall ratio is 25.7:1, 2nd gear is 17.6:1, 3rd gear is 10.0:1 and 4th gear is 5.57:1. At 7020 lbs, I normally use the third gear to accelerated up to either 25, 35, or 45 mph which is max speed in this town and 4th gear at speed drawing 75 to 125 battery amp and 200 to 300 motor while accelerating and 75 battery ampere or 200 motor ampere at 45 mph. I try the Uve Rick's EV Calculator and its way off on the Lithium battery with a EV weight of 5500 lbs. The 1st gear range is listed as 616 miles, the 2nd gear range is at 582 miles, the 3rd gear range is 537 miles, and the 4th gear range is 495 miles. I think if you delete the last digit in each number, it will be closed. At one time we had a formula to give a estimate range or is there another range calculator that can be use? Roland ----- Original Message ----- From: Lee Hart via EV<mailto:[email protected]> To: Electric Vehicle Discussion List<mailto:[email protected]> Sent: Thursday, July 31, 2014 12:48 PM Subject: Re: [EVDL] Lithium battery setpoints... Michael Ross wrote: > In air, aluminum oxide forms nearly instantly. Therefore, sanding > is a useless activity, if the goal is to remove aluminum oxide... You're right; aluminum oxide forms very quickly. However, the longer it is exposed to air, the thicker the insulating layer gets. So cleaning the terminal to remove the oxide immediately before assembly minimizes the thickness, and thus *does* reduce the resistance. Very thin insulating layers behave strangely. First, the very thin oxide layer is porous; it has lots of holes. Like spray painting something; before you have enough paint to completely cover, you can still see the underlying surface through the holes. With enough contact pressure, the metal can deform in to fill these holes to make contact anyway. Electrons can also "tunnel" across very small gaps even when there is an insulator in the way. The contact resistance doesn't go from 0 to infinite as soon as there is a tiny layer of some insulator; it gradually rises as the layer gets thicker. > I don't like the idea of sanding terminals. You want then to have the > flat machined surface they have leaving the factory o get a good bolted > joint with as much contact area as possible... What you think is a flat machined surface is actually a mountain range under a microscope. Machining, sanding, polishing etc. just reduces the scale of the mountains. When the two surfaces touch, only the peaks actually make contact. Increasing the contact pressure makes the metal deform, flattening the peaks, and improving the contact area. The deformations also break any oxide layer that may have formed, if it's thin enough and weak enough. (Aluminum oxide is a tough one, because it grows strong and thick). If you're bolting together steel, the contact pressures needed to deform it are tremendous. But lead, copper, silver, gold, and aluminum are all very soft metals -- it takes a lot less contact pressure to make them deform to improve the contact. > I suppose one might prove whether the resistance is changed for the > better if you have a really good instrument to check it. But this > will not be your garden variety multi-meter. It's pretty easy to measure what's happening yourself. The test is not difficult. I would urge people to try it themselves. It's especially enlightening with hard-to-connect metals like aluminum. You need a digital multimeter with a millivolt scale (usually 200mv or 400mv full-scale). And, you need a source of a known DC current of an amp or more. A 10-amp battery charger with a ammeter will do. Let's say you want to measure the resistance of the connections to a 12v battery: Run the battery down, so it will actually charge at 10 amps. Connect the charger at a point somewhat away from the battery, so the will be current is flowing in the wires and terminals you want to check. Set your meter to its millivolt scale. Connect one lead to the post of the battery itself. Connect the other lead to the terminal that connects to this post. Read the millivolt drop of the terminal, and the charging current from the charger. Use Ohm's law to calculate the resistance. For example: R = V / I = 10 millivolts / 10 amps = 1 milliohm (0.001 ohms) Under normal circumstances, 0.001 ohm would be a good connection. But it's a *bad* connection in an EV traction pack! At 100 amps, it would have a 1 volt drop, and so produce 100 watts of heat! Chinese lithiums I've tested straight from the factory are this bad, and sometimes worse! If you don't believe that cleaning, bolting, and contact "greases" help, try an experiment. 1. Get two pieces of aluminum that's been sitting around a long time. Bolt them together. Measure the torque if you can; if not, use a socket wrench and apply a "know" force. Measure the resistance between them (as described above). Notice that the tighter the bolt, the lower the resistance (to a point; then it doesn't matter any more). 2. Take them apart. Clean the two surfaces with sandpaper, file, wire wheel, etc. Clean off any resulting dust. Bolt them together again, and measure the resistance again at several different bolt torques. You will find that the resistance is lower, at every bolt torque (though it still reaches a point where more torque doesn't reduce resistance). 3. Add any kind of contact "grease". Noalox, axle grease, vaseline, etc. Repeat the test. You will find no difference in resistance, with or without the grease, no matter which one you use. But... leave the bolted pieces of aluminum outdoors for a while, where they will get hot/cold/wet/dirty etc. Without the grease, the contact resistance will go up. With the grease, it will stay about the same. This is a complex subject. I hope I have not oversimplified it too much. The experts already know it, and can ignore my analogies. But I hope those with only a little knowledge may gain some understanding. And, I hope people will *measure it for themselves*. That's far better than listening to experts debating how many electrons can dance on the head of a pin. :-) -- The definition of research: Shoot the arrow first, and paint the target around where it lands. -- David Van Baak -- Lee Hart's EV projects are at http://www.sunrise-ev.com/LeesEVs.htm<http://www.sunrise-ev.com/LeesEVs.htm> _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub<http://www.evdl.org/help/index.html#usub> http://lists.evdl.org/listinfo.cgi/ev-evdl.org<http://lists.evdl.org/listinfo.cgi/ev-evdl.org> For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA<http://groups.yahoo.com/group/NEDRA>) -------------- next part -------------- An HTML attachment was scrubbed... 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