9V LiPO charging circuit - Page 1
Forum section: electronics / beginners

author: alex-sh
author_rank: Regular Contributor
timestamp: February 13, 2019, 03:10:43 pm
content: Hello,I have Soshine 9V 650mA LiPO battery, which I want to use in my circuit.I use an external power supply DC 12-25V to be able to power the project/charge the battery.The project has got IC 7805 (input min 7V, max 25V) on input, therefore I can power the project directly from 9V battery. Project consumption is below 60mA. I have had experience with 3.7V / 7.4V LiPOs, but have no idea how to charge this 9V battery. There is an AC charger which comes with the battery.Could anyone please help me re designing a charging circuit?Many thanksAlex

author: Peabody
author_rank: Super Contributor
timestamp: February 13, 2019, 05:57:59 pm
content: There are a few Youtube videos on this product. It appears to be two LIPO cells in series, so really a nominal 7.4V battery, not 9V. But that means it may be possible to charge them as you would any 2S LIPO battery. But unless there is further circuitry inside the battery, you can't access the individual cells for charging, which could lead to unbalance problems. I think the RC guys know all about how to charge a 2S setup, but I never made it beyond 1S. Hope you find an expert here.

author: Audioguru
author_rank: Super Contributor
timestamp: February 13, 2019, 07:36:08 pm
content: The Soshine "9V" battery is 7 years old. There are newer 7.4V or 8.4V when fully charged Li-PO batteries available today.Nobody cares about balance-charging them, simply let it blow up then replace it.I charge ALL my 2-cells Li-PO batteries with a balanced 2-cells Li-PO charger. My "9V" Ni-MH batteries (6 or 7 cells?) do not last long.

author: alex-sh
author_rank: Regular Contributor
timestamp: February 13, 2019, 07:43:08 pm
content: Quote from: Peabody on February 13, 2019, 05:57:59 pmYeah, but non of these videos is about circuitry. At least I could not find one.Unfortunately, it is not 7.4V battery. It is more. I’ll measure voltage shortly

author: alex-sh
author_rank: Regular Contributor
timestamp: February 13, 2019, 07:47:33 pm
content: Quote from: Audioguru on February 13, 2019, 07:36:08 pmYou are correct. It is 8.2V. I fully charged it a month ago.Guys, I do not care about balance charging. I just need to charge the battery and have my project run on either (1) battery. Minimum voltage is 7V for 7805. (2) DC power 12-24VIf I do not find how to utilise this battery, i’ll just use a single 3.7V battery with a 9V boost converter. There are many options for a 1S

author: Nusa
author_rank: Super Contributor
timestamp: February 13, 2019, 08:03:44 pm
content: Quote from: alex-sh on February 13, 2019, 07:47:33 pm9V is just what they call it. As you say, it's 8.2V mostly charged, which means its a 2S arrangement under the skin of ~3.7V cells that should be charged to 4.2V each, or 8.4V together. Which is an arrangement you said you already knew how to deal with.

author: alex-sh
author_rank: Regular Contributor
timestamp: February 13, 2019, 08:23:42 pm
content: Yes, it is 2S. This makes it easy.I did notice another issue though. Minimum voltage in my case should be 7V.9V LiPO has a cut-off voltage of 5.5V. This is too low for me. This means I cannot use full battery capacity.I think this has to be abandoned in favour of a single 3.7V cell 2000mA. More juice and easy setup with a 9V boost converter. Did anyone use this module:https://www.ebay.co.uk/itm/USB-Lithium-Li-ion-Lipo-Battery-Charger-Module-3-7v-4-2v-Boost-Step-Up-5V-9V-12V/192683311240?hash=item2cdcd20088:g:q5cAAOSwt6Nbzb-tCheap and I suspect is probably rubbish?

author: Peabody
author_rank: Super Contributor
timestamp: February 14, 2019, 04:57:45 am
content: alex-sh, I suspect your Ebay module will work fine. It's a combination of the TP4056 charger and B62860 boost converter, which is the same as the MT3608. I used exactly that combination to get 9V, but using two separate modules. No reason why they can't be on the same board.But I do wonder what happens when USB is plugged in as far as isolating the battery charging from everything else. Ideally there should be a load sharing circuit to let USB directly power the boost converter so battery charging can proceed indepently to normal shutdown. But you can test for that when your module arrives.Thanks for finding the module.Nusa, yes they pretend it's 9V because it's in that standard package with 9V battery connectors. And for a lot of uses, it should work ok. By the way, did you see my video on multiplexing by segment? You and ogden got credit at the end.Now if I could just understand what balanced charging is.

author: Nusa
author_rank: Super Contributor
timestamp: February 14, 2019, 07:49:38 am
content: Quote from: Peabody on February 14, 2019, 04:57:45 amYes, I saw it. Glad you had fun learning how led matrices work. It's the sort of thing you will use again in the future.Balance charging is where you use some method to selectively favor one or more serial elements in a battery with the goal of having all elements end up in an equal state of charge. If you just charge the battery as a whole, you depend on all elements being so equal that they accept the same charge without direction. Batteries that are balanced charged, at least occasionally, generally last much longer than if they aren't. If you want to know more, just google "battery balancing" and start reading.

author: Zero999
author_rank: Super Contributor
timestamp: February 14, 2019, 09:19:29 am
content: Quote from: alex-sh on February 13, 2019, 08:23:42 pmWhy not swap the LM7805 with a low dropout regulator?http://www.ti.com/lit/ds/symlink/lm2940c.pdfhttp://www.ti.com/lit/ds/symlink/lm1085.pdfhttp://www.taitroncomponents.com/catalog/Datasheet/LM78D25.pdf

author: alex-sh
author_rank: Regular Contributor
timestamp: February 14, 2019, 09:48:31 am
content: Quote from: Zero999 on February 14, 2019, 09:19:29 amI cannot change it as the pcb is done and components are placed and I suppose there is no point - 95% time project will be powered by the external PSU. I am more concerned now about 5% - charging circuitry and the battery.PS I did just notice a few of the above LDOs have TO-220 package (my pcb footprint). I am going to order LM2940CT-5.0

author: Zero999
author_rank: Super Contributor
timestamp: February 14, 2019, 11:30:48 am
content: Quote from: alex-sh on February 14, 2019, 09:48:31 amThe pin-out of the regulators I suggested is exactly the same as the LM7805, so no modification of PCB layout is necessary.

author: alex-sh
author_rank: Regular Contributor
timestamp: February 14, 2019, 11:50:17 am
content: Quote from: Zero999 on February 14, 2019, 11:30:48 amI have noticed it too. Thank youIf I used 9V boost converter, there is no need to have an LDO.I need to come up with a battery charging circuitry first I think.

author: Peabody
author_rank: Super Contributor
timestamp: February 14, 2019, 07:59:43 pm
content: Do I understand correctly that the Soshine "9V" battery cannot be balance charged? If the only connection to it is the 9V connectors, there's no way to charge the two cells individually - no connection to the point where the two cells are connected in series.

author: alex-sh
author_rank: Regular Contributor
timestamp: February 14, 2019, 08:44:01 pm
content: Quote from: Peabody on February 14, 2019, 07:59:43 pmThat's correct. In fact, this is not only Soshine. Other 9V LiPO PP3 batteries are the same - there are only two contracts "-" and "+" and that's it.IMHO I do not understand why even bothering with balance charging. This is not a very expensive LiPO for a powerful quadrocopter or a car.

author: Audioguru
author_rank: Super Contributor
timestamp: February 15, 2019, 12:31:51 am
content: All the low dropout regulators I have seen need a certain fairly high value output capacitor to avoid oscillating. The LM2940 needs at least 22uF with very short leads.all my 2S Li-PO batteries for my RC model airplanes are charged safely with a balance charger.2 cells in series might develop one cell weaker than the other. If charged in series without balancing then the weak cell will become charged higher than the 4.2V limit which will cause a fire or explosion.

author: alex-sh
author_rank: Regular Contributor
timestamp: February 15, 2019, 12:54:15 pm
content: Quote from: Audioguru on February 15, 2019, 12:31:51 amThere is protection in place for overcharging / cut-off.The problem is that without breaking the battery I cannot have access to balance charge it. There are only two wires "-" and "+" as on any PP3 battery. That's it. Balance charging is not an option with this battery.

author: Zero999
author_rank: Super Contributor
timestamp: February 15, 2019, 01:50:00 pm
content: Quote from: alex-sh on February 15, 2019, 12:54:15 pmEach cell should already have built-in protection to prevent fire.I'd be more worried about over-discharging, then trying to recharge it, which can cause fire. Again there should be a built-in protection system, but it might be a one-shot: once the battery voltage drops below a certain level, the cells will go open circuit and no recharging possible, without dismantling the battery. The circuit or power supply should have a separate undervoltage cut-off circuit which activates before the battery's built-in protection system.

author: Peabody
author_rank: Super Contributor
timestamp: February 15, 2019, 03:01:19 pm
content: I've found a lot of tutorials on balanced charging, parallel charging, etc., but they basically start with an already existing charging device, and pretty much only deal with how to connect batteries to them. Does anyone know of a good tutorial that deals with what actually happens, including circuits if possible? So for example, how does the device in the picture work?

author: Nusa
author_rank: Super Contributor
timestamp: February 15, 2019, 11:28:28 pm
content: Try this to give you an idea how they might work.https://www.electronicdesign.com/power/look-inside-battery-management-systems

author: alex-sh
author_rank: Regular Contributor
timestamp: February 18, 2019, 09:12:59 am
content: Not sure why we are discussing balance charging.Soshine 9V Lipo or any other similar LiPO does not have any other leads but "+" and "-". Balance charging is not possible.BTW - I did check their web-site. Funny enough, it says "New 9V Li-po Rechargeable: 650mAh 7.4V"http://www.soshine.com.cn/a57.aspxThe battery is sealed.