| Electronics > Beginners |
| Switching from Nicad battery to Lipo: Am I doing this right? |
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| Nohippychicks:
--- Quote from: kjr18 on July 29, 2018, 12:47:07 pm --- First problem: Your battery protection ic triggers because of too high current draw. Solution for this is to use different source. ... --- End quote --- I think this is the issue here! I'll take a picture of what I have when I get home, but that beautiful Paint rendition is pretty much the way I have it hooked up and those even look like the same charge circuits and boost converter I'm using, but it's tough to tell for realsies. |
| kjr18:
I did some "tests" using a power supply, a boost converter and some load. With 300mA load at 12.8V this crappy chinesium boost converter takes 1.3A at 4V. With 500mA load at 12.8V it's 2.3A at 4V. With 1A load at 12.8V it takes 3.7A at 4V. What a piece of crap, 60% efficiency. You can use some notebook power supplies with some buck converters to drop voltage a bit, to desired level. |
| KL27x:
^ But... 4kAh LiPo can output at least 40 amps without batting an eye. And possibly close to 200. Depending on what kind. The discharge protection on the charge controller does not measure current, does it? It measures voltage, no? I think it doesn't care how much current is passing unless it causes a voltage drop below threshhold, which will be around 3V, min. Most popular cutout probably 2.9V and under. That size LiPo will sustain 3.3V+ easy at 40 amps. So the max current output cutout depends on the output impedance of the battery, which in this case is really really low. I would suspect the boost circuit is the potential weak link, here. This can* cause the radio to not function. But this shouldn't create the 1.1V readings (unless there is some additional problem/malfunction/miswiring). *I have no idea what the current draw of the radio is. But at any load, it shouldn't happen like what the OP described. If the output FET of the charge controller is tripping, there should more than likely be some other malfunction. The 5/6 pin SOT could be a dual voltage detector. It could theoretically sense the voltage drop across the output FET as a true max current shutdown. I'd be curious if it is wired up like that. OP could tell by looking at the traces coming off of it. Just looking at the pics, it does not look like this is the case. Edit: Ok I didn't find a datasheet. But I found this video. I can't listen to the whole thing, but I scanned, and HE has a copy of the datasheet. At 1:08/9 is where you can get a peek that shows it. The FET is a dual FET. It lists voltage of the second detector to be 150mV. It probably measures the voltage drop across the output FET. How many amps that translates to, I don't know. And it looks like thm_w figured all this out sometime last year. I'll be busy removing foot from mouth. |
| Nohippychicks:
Ok, I finally got home so I could piddle around with this thing again.. I attached a picture of the little setup I have, and I'll edit this post if it doesn't show. The white and red wires opposite of my hand are nothing, they were part of the old battery and attach to a little barrel jack. The black wire swinging in the breeze is the negative out of the boost converter and is normally attached to a negative terminal on the other half of the plastic battery housing, I removed it for clarity. Of course, the circuit stuck to the side of the battery is the boost converter and the other is the charge circuit, which I feel is the culpret. I was able to get a semi-reliable connection to my meter and wall wart. With the radio not programmed, I can't transmit even to test, so the most load I was able to get was by turning on the back light. I read .066A with the radio on and squelch off and .101A with the backlight on. I think tomorrow, or maybe Tuesday, my newer charge controller should arrive. I should get a steady output from that one...and if that's the case and all this is fixed, I'll steer clear of buying the cheapest stuff I can get from now on, maybe. Once again, thank you all for the help in this! |
| KL27x:
I found the datasheet for the output protection IC. I wondered if/how one could increase the output current threshhold. --- Quote ---The discharge overcurrent detection voltage (VDIOV) is V6 when VDO is set to "L" after increasing V6 gradually from the initial status 1. 2. 4 Load Short Circuit Detection Voltage (VSHORT) The load short circuit detection voltage (VSHORT) is V6 when VDO is set to "L" after increasing V6 gradually after setting S3 to ON from the initial status 1. 2. 5 Charge Overcurrent Detection Voltage (VCIOV) The charge overcurrent detection voltage (VCIOV) is V6 when VCO is set to "L" after decreasing V6 gradually from the initial status 1. --- End quote --- --- Quote ---I think tomorrow, or maybe Tuesday, my newer charge controller should arrive --- End quote --- Good plan. Just plugging in a vanilla guesstimate of 100R tops for the Rds of the output FET, and overcurrent voltage detector of 150mV, that puts the max current in the ballpark of 1.5A, min. Perhaps up to something like 10A realistically, on the high end (unless it has charge pumps for the gate driver). This is just guesswork from what I understand in there. I just can't figure out that datasheet. It's a doozy. I suppose there's some oscillation of this circuit if that is what is creating the 1.1V. It 'posedly has some hysteresis/smarts, but damned if I can read that schoo. --- Quote ---With 1A load at 12.8V it takes 3.7A at 4V. What a piece of crap, 60% efficiency. --- End quote --- I had to do a doubletake; I would be happy with those numbers on my own boost circuit. So with my calculator, I come up with 86.5% :-// |
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