tag:blogger.com,1999:blog-369941762441967690.post8779216390041023424..comments2022-11-26T01:46:19.151-08:00Comments on EV Z3: Charging Mystery SolvedTim Catellierhttp://www.blogger.com/profile/02801279544184321528noreply@blogger.comBlogger5125tag:blogger.com,1999:blog-369941762441967690.post-79364875757794716302010-11-21T06:15:43.014-08:002010-11-21T06:15:43.014-08:00Tim:
I am a EE. I actually don't do that but...Tim:<br /><br />I am a EE. I actually don't do that but have the training and used to. It has taken two years to realize what is happening with these chargers because it happens with SOME of the chargers. What I don't know is how the other chargers get around it.<br /><br />The Brusa and the Elcon seem to allow me to set a voltage, and in the case of the Elcon, set it by e-mail, and it hits it within 0.6 volts and doesn't seem to matter how long or what kind of wires I use to connect it. It does NOT have separate sense wires.<br /><br />The Manzanita I had reported as having a 4.5v rise on the end AFTER you set the voltage. it does, but for the same reason. As the CURRENT decreases, the voltage drop across the cable ALSO decreases, and so it LOOKs like the voltage is rising. Not apparent since you can't see anything on the charger end - no meter.<br /><br />We're testing a new charger prototype right now - exactly the same problem. It cannot sense voltage accurately, and it varies depending on current.<br /><br />So don't feel mystified. It's taken me two years to figure out what's going on here. And as you have learned, that voltage is important on LiFePo4 cells in a way that just doesn't really matter on lead acid cells.<br /><br />I THINK this is what has led Rich Rudman to decide he HAS to have a BMS to shut off his charger or it "destroys" cells. He doesn't. But setting the voltage as you have learned is a little tricky. And you have to change it when you change current levels.<br /><br />Jack RickardJack Rickardhttps://www.blogger.com/profile/15936311474215791697noreply@blogger.comtag:blogger.com,1999:blog-369941762441967690.post-33868024750883745652010-11-20T21:10:57.908-08:002010-11-20T21:10:57.908-08:00This is the kind of problem I run into since I'...This is the kind of problem I run into since I'm not an EE. Not only do I not fully understand the problem, but I lack the knowledge needed to put the problem to words so that others can understand it.<br /><br />I had NO experience with electrical work before this project. Consequently, when something like this happens, not only am I completely caught off guard, but I'm at a loss to explain what caused it. The best I can hope for is to tinker around until I can repeat it and recognize a pattern in the behavior, and then adjust my plan accordingly. <br /><br />I've understood since this post WHAT was happening, but I really didn't know WHY. Thanks for the explanation Jack! If I'm not mistaken, this sounds like the effects described by Ohm's law. I've heard of Ohm's law before, but I never knew how to apply it or how it would affect me. I've got a lot to learn. It's a good thing I enjoy it.Tim Catellierhttps://www.blogger.com/profile/02801279544184321528noreply@blogger.comtag:blogger.com,1999:blog-369941762441967690.post-75450039078719937082010-11-19T21:21:16.906-08:002010-11-19T21:21:16.906-08:00We've run into this a bit. I've reread and...We've run into this a bit. I've reread and get it now.<br /><br />The Manzanita, like some chargers, is measuring the voltage at it's output. Let's say this reads 166 volts. Yo u aren't show this voltage, you measure it at your batteries as 163 volts.<br /><br />Where's the difference? 25 amps through the cables. The batteries of course get this current at the end, and the cables do have some resistance. This voltage drop will be a function of the resistance and the current through them. E=IR. If the difference is 3 volts at 25 amps you have a resistance of 3/25 = 0.12 ohms.<br /><br />So let's drop this currrent to 15 amps. 15 x 0.12 does not equal 3 volts. It equals 1.8v. So instead of measuring 166 volts which is set and putting 163 to the cells, you are now measuring 166 and putting 164.2 to the cells.<br /><br />So your pack charge voltage rises to 164.2 by the act of turning down the current to 15 amps.<br /><br />Hope this helps.<br /><br />keep up the great work.<br /><br />Jack Rickard<br />http://EVTV.meJack Rickardhttps://www.blogger.com/profile/15936311474215791697noreply@blogger.comtag:blogger.com,1999:blog-369941762441967690.post-8878830439556551802010-10-24T11:05:04.342-07:002010-10-24T11:05:04.342-07:00Hi Jack,
I appreciate your help. I never claimed ...Hi Jack,<br /><br />I appreciate your help. I never claimed to be an expert on any of this, so the more advice I get the better. Unfortunately I don't have a learned sage over me smacking my hand when I attempt something stupid.<br /><br />I had decided to do just what you've said, and essentially give up the top end. I had no intention of playing around with the cut off voltage once it was set, but I discovered this oddity in the charger's behavior when I changed the current input. Now I have that to contend with. <br /><br />At this point, if I charge to a 164 cut off, by the time the charger has ramped down and shut off, the highest battery is under 3.5 volts. That seems plenty safe to me. Do you disagree?<br /><br />Since the over charging episodes mentioned in the post, I've made sure they've never gone above 3.6. It took a lot of watching, and adjusting but my goal all along has been to make sure none travel north of 3.5. <br /><br />I do wish I'd never tried to balance them, but that milk is spilled so I have to live with it. I realize that the best way to maximize their life now is simply stay in the limits.Tim Catellierhttps://www.blogger.com/profile/02801279544184321528noreply@blogger.comtag:blogger.com,1999:blog-369941762441967690.post-41094585646876047542010-10-24T10:03:54.651-07:002010-10-24T10:03:54.651-07:00Tim:
You're killing me here watching you stru...Tim:<br /><br />You're killing me here watching you struggle with these chargers and batteries. You're wearing the spots off of em. <br /><br />So drop your charge voltage to 160 and leave em alone. They will INCREASE in capacity and then they will DECREASE in capacity and not at all in lock step. But you're dinking around with 150 wH of power playing with it at the top.<br /><br />The cells will last much longer if you avoid the two ends. T hey are not "sliding around". You did a BAD thing top balancing them. Bottom balancing them now is a LOT of work. So just give up the top end. Lower your voltage and take a smaller pack. If you're driving to the bottom endge anyway, you're not out anything.<br /><br />You're gradually working your way around in a great big circle right back to where I started you out at. <br /><br />At least you're measuring and observing. You will eventually learn this way.<br /><br />Jack RickardJack Rickardhttps://www.blogger.com/profile/15936311474215791697noreply@blogger.com