Battery charger IC in a device not charging the battery - Page 1
Forum section: electronics / general

author: psysc0rpi0n
author_rank: Frequent Contributor
timestamp: February 06, 2025, 04:04:42 pm
content: So, I'm using a Lilygo T-SIM7600G-H and this device is using a CN3165 IC to control the charge of a single Li Ion cell.The datasheet says this IC should have a Vin betwen 4.4V and 6V.The circuit around the IC and also the battery protection circuitry is attached below. I took it from the Github of the device, yes it's open source!Ok, I'm using a small solar panel, rated at 5V, 2.5W and 500mA to charge the battery. But something is not working.If I place the solar panel outside and measure the voltage at OL, I get easily 5.90V. However, when I plug the solar panel to the device, this voltage drops to a very fixed 4.35V and therefore, no charge is happening because the CN3165 is supposed to operate within 4.4V-6V range.What and/or why is this voltage drop happening? The LilyGo device is powered OFF, so, proabbly only a neglectable load should be observed, and not enough to bring the solar panel voltage down to a point where the CN3165 is not being "activated".Does anyone have an idea why the CN3165 seems to be kind cutting down the solar panel voltage?PS: I tried the following and the charger IC seems to be working. I injected 5V to SOLAR_IN pin from an external power supply. I was also using a not fully charged cell and I could see that the cell was being charged! Current being pulled by the charger was around 500mA~600mA...

author: tunk
author_rank: Super Contributor
timestamp: February 06, 2025, 04:22:48 pm
content: Most likely the panel cannot provide enough power.The "5V, 2.5W and 500mA" is a absolute maximumat ideal conditions (or quite a bit less if it's fromaliexpress, ebay etc.). You could e.g. try to adjustISET to 100mA and see if it works.Edit: You could try to measure the current from thepanel, it may be charging.

author: tooki
author_rank: Super Contributor
timestamp: February 06, 2025, 04:42:28 pm
content: For what it’s worth, there are special charger chips and DC-DC converter chips designed precisely to deal with this situation (where loading down a solar panel causes its voltage to collapse). They use an approach called MPPT (maximum power point tracking) and essentially will back off the current draw to find the point where the maximum wattage can be extracted.

author: tom66
author_rank: Super Contributor
timestamp: February 06, 2025, 04:51:39 pm
content: Yep, this is clearly a foldback issue.The principle issue with a solar panel is you can model it as a voltage source with a resistor (kinda) in series.You do not know what that resistor or voltage will be (it is sunlight, temperature, age dependent). The manufacturer of the solar panel will provide some characteristics like the open circuit voltage (Voc) and the short circuit current (Isc). These will be given in the best case, maximum illumination of the panel, desert sun at noon kind of conditions. And if the panel is source from Aliexpress or eBay expect the figures to be goosed by a further 2-3x.The problem here is because you do not know these figures, other than the maximum, you cannot just apply any load to a panel and expect it to work. If you try to go past the Isc, the panel voltage is zero. If you want to get the most power out of the panel, itusuallyends up being somewhere around 80% Voc and 80% Isc... but again, sunlight/temperature/age dependent. Finding the actual point requires a controller that can test the panel. An MPPT controller will do one of a few things, the most common algorithm is 'perturb and observe', the load will be slowly increased until a local maxima in power is reached. The controller will then slowly oscillate around this point, searching for an increase in power (as the illumination or temperature changes). The best controllers can get 99% of the MPPT power.One solution to this problem is to just charge the cell very slowly, so that you know that during daylight with a 50mA load, you will get enough voltage from the panel to be able to charge the battery... but this isn't ideal as the panel will need to be significantly oversized for the charging of the battery.

author: Peabody
author_rank: Super Contributor
timestamp: February 06, 2025, 05:15:48 pm
content: Do you have a multimeter that will measure DC current up to maybe 1 Amp, or at least 600mA? If so, take just the panel out into full sun, and measure the short-circuit current. With the meter in DC current mode, connect the leads directly across the panel ouput. That will give you an idea of whether the panel is any good. If it's anywhere close to 500mA, then the panel is not the problem.Then connect the panel back to the circuit, take it back out into full sun again, and measure the voltage on the drain and source of Q6 when the panel voltage is 4.35V. The voltages should be almost the same.

author: psysc0rpi0n
author_rank: Frequent Contributor
timestamp: February 06, 2025, 05:18:51 pm
content: Ok, I did the following test and to be honest, I don't even know how to interpret the result.The panel is not from Aliexpress or ebay. It's from a local shop. Where the local shop got it, I don't know. But cannot grant that it's not one of those.Anyway, I have here those high power resistors. One is 5W, 5 ohm and the other 5W, 4 ohm. I connected each one from the positive to the negative leads of the solar panel and put the DMM in series to measure current.What I get is not what I expected to get, at all. I got around 5.8mA of current flowing, for around 4.71V (OL measurement before adding the resistors).So, I was expecting something like 4.71V / 5ohm = 0.942A and 4.71V / 4ohm = 1.178A. So, way too far from what I got! I'm doing something wrong for sure, no?

author: psysc0rpi0n
author_rank: Frequent Contributor
timestamp: February 06, 2025, 05:20:30 pm
content: Quote from: Peabody on February 06, 2025, 05:15:48 pmOk, good one. I didn't remember to do that.Toorrow I'll do that. Sun is almost gone here (almost at the end of the work day) and probably not the best time to do those tests!

author: tunk
author_rank: Super Contributor
timestamp: February 06, 2025, 05:43:26 pm
content: I assume you have an 18650 cell?You could try to bypass the charging circuit andonly use a BMS and Schottky diode. Not ideal,but I think that's used in cheap solar power banks.

author: tom66
author_rank: Super Contributor
timestamp: February 06, 2025, 06:08:17 pm
content: Quote from: tunk on February 06, 2025, 05:43:26 pmThis is a bad idea. It's okay to do it with Ni-MH (no risk of fire), but not with Li-Ion. It is possible to cause dendritic damage to a Li-Ion cell by overcharging it, which can result in fire, even if the energy source cannot supply the required current to put the cell into a thermal runaway condition itself.

author: Peabody
author_rank: Super Contributor
timestamp: February 06, 2025, 06:22:18 pm
content: I have a solar panel with the same specs as yours, and I've confirmed that it meets those specs. It is this one:https://www.amazon.com/ALLPOWERS-Battery-Charger-Encapsulated-130x150mm/dp/B074TYH68ZNo longer available on that listing, but seems to have several sellers on eBay. Apparently Allpowers is a legit company.Today is overcast, and I'm in winter, but when I put the meter and the 5R resistor in series across the panel, I get about 25mA. Without the resistor, it's about 27mA. Full open-circuit voltage today is 5.35V. Normally in full summer sun that would be around 5.85V, so as I said, overcast.It may be that your panel is just not as capable as the specs say. But you really need to test it in your full summer sun. You already know the open circuit voltage is 5.9V, which is right for a 5V panel. But the key test is the short circuit current test. That should be somewhere close to 500mA. It may only be 400mA because the spec is probably at the maximum sun you would get at noon on a perfectly clear day at the top of Mt. Kilimonjaro. But 400mA is close enough.And we need to be sure that Q6 is fully turned on.Edit: You are doing all of this solar stuff with nothing plugged into the USB port, right?

author: psysc0rpi0n
author_rank: Frequent Contributor
timestamp: February 07, 2025, 08:50:58 am
content: Quote from: tunk on February 06, 2025, 05:43:26 pmHum, ok, but even if I wanted to do that, I couldn't because I don't have here spare parts. And someone said it could be potentially dangerous, so I'll avoid it as I'm not very experienced with Li Ion cells either!Quote from: tom66 on February 06, 2025, 06:08:17 pmOk, I won't even try it, and even if I wanted, I couldn't because as I just said above, no spare parts! Thanks for warning.Quote from: Peabody on February 06, 2025, 06:22:18 pmMy solar panel was purchased in a local store. But obviously I don't know where do they get them from. They may also purchase them from China or so.Yeah, it's raining here today but I'll measure the short circuit current to see what I get even in a rainy day like today. After all I also need to know what the panel is capable in wrost case scenarios!PS:yeah today is not good for SC measurements.V_SC = 3.58V ~ 3.62VI_SC = 1.08mA(I really think this value should be way higher even in poor conditions like today)

author: tom66
author_rank: Super Contributor
timestamp: February 07, 2025, 02:16:57 pm
content: Generally I'd expect a panel to produce 10-20% of the normal output power in overcast conditions. It sounds like a defective or fake solar cell.I assume V_SC in this case is V_OC, open circuit voltage? As short circuit voltage should be zero, otherwise it is not a short. The V_OC should be able to reach around 4-5V if it is a 5V cell with even reasonable illumination.

author: Peabody
author_rank: Super Contributor
timestamp: February 07, 2025, 03:06:30 pm
content: Yes, those numbers seem pretty low. But earlier you reported 5.90V OC voltage. Was that in bright sun?The panel will respond to artificial light too, like maybe a car's headlight or a high-wattage spotlight. But you really need a good sunny day to find out for sure if your panel is up to the task.

author: Peabody
author_rank: Super Contributor
timestamp: February 09, 2025, 07:51:59 pm
content: I finally got a clear day here. With my panel pointed directly at the sun, I get very slightly above 500mA short circuit current. So your panel should come close to that. My panel measures 15 x 13 cm.

author: psysc0rpi0n
author_rank: Frequent Contributor
timestamp: February 10, 2025, 12:03:34 pm
content: Quote from: tom66 on February 07, 2025, 02:16:57 pmWell, today I went outside again. It's cloudy but there is plenty sunlight.V_OL = 5.99VAnd at some point, I was able to measure around 180mA of short circuit current. But then, like a couple of minutes later, I tried to measure again the short circuit current, and values were very low again.I'm going outside again to try once more to check the V_OL and short circuit current!Quote from: Peabody on February 07, 2025, 03:06:30 pmYes, the 5.90V were V_OL and not really bright but the sunlight was pretty good. Cloudy day just like today but the sunlight is abundant!Quote from: Peabody on February 09, 2025, 07:51:59 pmMine is also 15 x 13 cm but I could only get around 180mA!Edited;Yeah, somehow I cannot measure any reasonable short circuit current right now! Either the solar panel is defective or the DMM is doing something wrong! The V_OL seems reasonable. Right now, I have the solar panel next to a window and V_OL = 5.24V.

author: tom66
author_rank: Super Contributor
timestamp: February 10, 2025, 02:32:25 pm
content: So, rough numbers, if V_MPP is 80% of V_OC, and I_MPP is 80% of I_SC, you have a 700mW panel, capable of 4.8V @ 140mA. Not a 2.5W, 500mA panel. Sadly, many panels are oversold on capability - though you will need to be sure that you are testing under the same conditions that the manufacturer claims. I imagine the weather in Argentina is pretty good right now, but I do not know for sure about your local conditions. There should be no clouds and testing should be done around noon if possible with a direct line of sight to the sun. Try adjusting the panel angle to see if current changes. The best angle is parallel with the sun's rays.

author: Peabody
author_rank: Super Contributor
timestamp: February 10, 2025, 02:40:46 pm
content: Also make sure nothing is shading any part of the panel. What model meter are you using?

author: psysc0rpi0n
author_rank: Frequent Contributor
timestamp: February 10, 2025, 02:42:56 pm
content: Quote from: tom66 on February 10, 2025, 02:32:25 pmYeah, the problem is that I cannot measure any short circuit current right now! Just for a small test, I built a small circuit with a 555 timer, a couple of resistors, capacitors and a LED, and the panel is close to a window and the circuit is working. However, this is a very low power circuit, but it's working.i'm going outside again to try to measure short circuit current once more. I'll report in a few minutes!I'm in Portugal and weather is partly cloudy yet sunny...Edited;Well, this is weird and I don't know why this happens but my multimeter, which is a UNI-T UT33D, when I set it to 2000uA scale, it read 8uA, if I set it to the 20mA scale, it reads 0.08mA, when I set it to the 2000mA scale, it reads 0.8mA and when I set it to 10A and change the black probe to the 10A plug, it reads around 0.11A. (I forgot to measuer the V_OL though).

author: Peabody
author_rank: Super Contributor
timestamp: February 10, 2025, 03:10:19 pm
content: The black probe? Can someone clarify which probe should be moved to the 10A socket? I thought the black probe is always in the COM socket, but I don't have a meter like this. Anyway, does someone know for sure?

author: tom66
author_rank: Super Contributor
timestamp: February 10, 2025, 03:19:03 pm
content: Your country flag shows Argentina -- but if you are in Portugal you are in winter and the sun level is not that much better than the UK right now. So you cannot expect the full performance even with a sun tracker.Also, it sounds like your meter might have a blown fuse for the low current range.

author: tunk
author_rank: Super Contributor
timestamp: February 10, 2025, 03:22:49 pm
content: Quote from: psysc0rpi0n on February 10, 2025, 02:42:56 pmMultimeters measure current indirectly by measuringvoltage across a resistor. Low current ranges usehigher resistances than lower ranges. This explainsthe different current readings you see.Edit: It's called burden voltage:https://www.eevblog.com/forum/blog/eevblog-1604-beware-multimeter-burden-voltage/

author: Peabody
author_rank: Super Contributor
timestamp: February 10, 2025, 03:24:09 pm
content: I want to comment on this from the first post:QuoteWhile the datasheet says 4.4V is the minimum normal operating voltage, if you read through the description, it says charging will begin if the input voltage is above the UVLO voltage, which is 2.4V. Beyond that, the input voltage just has to be higher than the battery voltage, plus a little headroom for the circuit to operate properly. This is a linear charger, so the battery won't charge otherwise. But at 4.35V input from the panel, it is almost certainly charging the battery. It is fixed at that level because the battery is a low-impedance current sink at its current voltage, plus that headroom voltage, and the panel simply provides as much current as it can at that voltage.So if you can measure the current flowing from the panel, I think you will see that some charging is going on.Re my previous post, the black lead should go in the COM port, and the orange lead in the 10A jack to measure the current. If you get less than 0.2A, then you should also get a similar reading in the 200mA range with the orange lead moved back to the center jack. If you get nothing from the 200mA range when you know the current is actually there, but not over 200mA, then you need to replace the fuse.Edit: It looks like the UT33D has the COM jack on the right, and I assume that's what you have. However, the UT33D+ seems to have the COM in the middle. Either way, the black lead always goes in the COM jack.

author: Peabody
author_rank: Super Contributor
timestamp: February 10, 2025, 03:35:16 pm
content: Lisbon is within one degree of lattitude from me, so we should get the same results if our panels are the same size and have the same specs. I get 500mA SC current around noon on a clear day, with the panel pointed directly at the sun.

author: psysc0rpi0n
author_rank: Frequent Contributor
timestamp: February 10, 2025, 04:06:25 pm
content: Quote from: Peabody on February 10, 2025, 03:10:19 pmThere are some DMMs which you need to change the probes to measure current. Some other DMMs doesn't need this. Yet some other DMMs have a socket for higher currents because they also have a proper fuse for these higher currents which is the case of the DMM I have with me. With this DMM, I don't need to change the probes up to 200mA. And there is a 3rd socket for currents up to 10A. I know I didn't need to do this but I was suspecting that the fuse of the lower currents could be blown up, so I tried to measure current with the 10A socket!And sorry, I meant the red probe. Not the black, of course!Quote from: tom66 on February 10, 2025, 03:19:03 pmYeah, I know about the flag. But I'm in Portugal.Quote from: Peabody on February 10, 2025, 03:35:16 pmI'll bring my own DMM tomorrow to check if there is something wrong with the DMM I have at work. I can't measure any reasonable currents right now but the 555 timer circuit works!I also checked visually the 200mA fuse inside the DMM and it looks like the wire is intact but I'm not 100% sure! Tomorrow I'll make sure of the fuse and also the current of the solar panel using my own DMM which is a bit better than this one. It's a Brymen 869s

author: tunk
author_rank: Super Contributor
timestamp: February 10, 2025, 04:27:30 pm
content: Quote from: psysc0rpi0n on February 10, 2025, 04:06:25 pmYou can check the fuse with the UT33D itself by taking it out, andtest it with the continuity/diode range. It should beep if it's ok.

author: psysc0rpi0n
author_rank: Frequent Contributor
timestamp: February 11, 2025, 11:49:12 am
content: Quote from: tunk on February 10, 2025, 04:27:30 pmI just checked and yes, the 200mA fuse is blown. No continuity. I also checked with my Brymen.Today is cloudy and the solar panel can only go up to around 4.75V (V_OL).But it can still feed the test circuit I put on a breadboard (555 astable oscilator).So, I guess I can conclude that the Solar Panel is not providing enough power to the device when connected to it.But I still want to go outside with my DMM and measure Short Citcuit current again. To see if I get any reasonable values even for a cloudy day!

author: Peabody
author_rank: Super Contributor
timestamp: February 11, 2025, 03:42:39 pm
content: Quote from: psysc0rpi0n on February 11, 2025, 11:49:12 amAs I stated in Reply #21, if the panel voltage is 4.35V in full sun when supplying the charging circuit, it almost certainly is charging the battery, although possibly with not much current. The UVLO voltage (undervoltage lock-out) is 2.4V, not 4.4V. While 4.4V may be the "normal" minimum operating voltage to get to a full charge in a reasonable time, charging will take place at any input voltage that's about 0.2V higher than the battery voltage. I suspect if you left it charging, the voltage would increase from 4.35V to well over 4.4V as the battery charges. Does the Charging LED light up?QuoteYou should be able to measure SC current with the UT33D on the 10-amp jack and scale, or on the Brymen even on the mA scale, which goes up to 600mA.

author: psysc0rpi0n
author_rank: Frequent Contributor
timestamp: February 11, 2025, 05:16:57 pm
content: Quote from: Peabody on February 11, 2025, 03:42:39 pmI already did the test and the battery didn't go up past 2.99V or 3.00V. I left the battery and the solar panel connected for like 2 days and the battery voltage stopped at around 3V.There is a red led and a green led and if I understood correctly, while the red led is on, the battery should be charging. When the charge is complete then the red led goes off and the green led turns on. But I've never seen the green led to turn on while charging batteries with the solar panel. Only way to see the green led is to charge the battery with an external power supply and when it is charged, place it in the device and connect the solar panel. Only then the green led turns on.About the short circuit current, on a cloudy day like today I could only measure around 23mA. The other day, with plenty sunlight, I was able to measure 180mA. But still looks like to low values! I have to wait for better days to test the short circuit current again!

author: Peabody
author_rank: Super Contributor
timestamp: February 11, 2025, 11:33:02 pm
content: Well I'm confused. In your first post, you said:QuoteAre you saying with the panel generating 4.35V the battery doesn't charge past 3V?Edit: Q6 sits between the solar input and the charger. Maybe that's not turning on fully with the panel being the only power input. With the panel connected to the circuit, but not USB, can you measure the voltage on physical pin 4 of the CN3065, and the panel voltage? They should be almost the same.

author: tom66
author_rank: Super Contributor
timestamp: February 12, 2025, 09:57:34 am
content: Q6 might not be turning on fully if VBUS is floating, perhaps add a 100k pull down to it to ensure it does go to ground when there is no USB connection. I assume the purpose of this circuit is to allow USB or solar to be used, but if you do not need USB function, you can delete Q6 and D4 and feed directly into C7.

author: Peabody
author_rank: Super Contributor
timestamp: February 12, 2025, 03:17:54 pm
content: I found the full schematic here:https://github.com/Xinyuan-LilyGO/T-SIM7600XIn the VBUS-VCC4.2V section on page 4 of the schematic, it shows Vbus pulled down through two 100K resistors in series. So that shouldn't be a problem. But Q6 could still just be bad. Measuring the voltage drop across Q6 should make things clear.

author: psysc0rpi0n
author_rank: Frequent Contributor
timestamp: February 12, 2025, 05:54:47 pm
content: Quote from: Peabody on February 11, 2025, 11:33:02 pmYes, that's what I was saying.I'll make those measurements tomorrow if weather is sunny. It has been cludy and rainy for the last 2 or 3 days!Quote from: tom66 on February 12, 2025, 09:57:34 amThat was one of my initial questions. I couldn't figure out if the solar panel was supposed to feed the circuit AND charge the battery or ONLY to charge the battery. But from what I was said by support, and if I understood what they told me, the panel won't be able to feed the circuit, mostly because if there is a SIM card working with 4G, the current needed is higher than what most panels can provide. So, I assume the circuit is made to only charge the battery!Quote from: Peabody on February 12, 2025, 03:17:54 pmYes, chematics are in Github but some of the components have changed over time and schematics weren't updated. It's the case of the charger IC that is the CN3065 in the schematic but was changed to a CN3165 on the revision of my board of the device I bought!

author: psysc0rpi0n
author_rank: Frequent Contributor
timestamp: February 13, 2025, 02:25:32 pm
content: Ok, today is somewhat sunny and also partially cloudy but I went outside with the panel alone and my DMM and today I could measure the short circuit current of the panel at around 470mA, so quite close to the stated value!And the V_OL was around 6.001V.Then, I came inside to pick the device and a battery at storage voltage (at around 3.8V) and I took it outside to plug the solar panel to it. Then I measured the voltage at the panel input on the device and the voltage is around the same 4.35V. However, in this case, I think the battery is charging. I left the solar panel and the device outside and I came inside to reply here. I'll give it some time and will measure the battery voltage later to see if it charged anything or not!

author: Peabody
author_rank: Super Contributor
timestamp: February 13, 2025, 05:52:23 pm
content: Is the device switched off while the panel is charging the battery?

author: tom66
author_rank: Super Contributor
timestamp: February 13, 2025, 09:51:34 pm
content: Quote from: psysc0rpi0n on February 12, 2025, 05:54:47 pmThe circuit will draw power from either solar or USB. If USB is present, solar input is disabled. The way this is achieved is Q6 is a PFET. The PFET gate is pulled down by two 100k resistors (as @Peabody notes). That means if USB is present, the source of the PFET will be at ~5V minus one diode drop due to D4, say 4.5V, and the gate will be at VBUS, so Vgs=+0.5V, and the transistor will be switched off. (PFET needs a negative bias wrt to source to turn on.) If, instead, USB is not present, assuming some solar energy is present, the gate will be near ground via the 100kohm resistors, and the source will be high due to the solar panel, so the PFET will turn on hard. The body diode (parasitic element) inside the PFET provides the initial bias, and then the PFET switches on. This circuit avoids the need to use a diode for the solar panel input which is typically the one you need to be the most efficient.

author: Peabody
author_rank: Super Contributor
timestamp: February 13, 2025, 10:50:12 pm
content: Yes, but as far as I can tell, there's no path from the panel around the charger to supply the load directly. In other words, there's no load sharing or power path circuit around the charger. So that may mean that power to the rest of the circuit has to be cut off when you're charging. Otherwise the CN3165, which can only supply 1A, has to source the charging current and the load current at the same time. Do we know what the circuit draws when operating?

author: psysc0rpi0n
author_rank: Frequent Contributor
timestamp: February 17, 2025, 09:39:41 am
content: Quote from: Peabody on February 13, 2025, 05:52:23 pmSorry the late reply. Yes, it was turned off while the battery was charging.Quote from: tom66 on February 13, 2025, 09:51:34 pmOhh, thank you for the clear explanation. that really helps to understand how the circuit works! I wouldn't be able to perform that analysis even though I should be able!The 100k pull-down resistors you refer are the ones in page 3 of the schematic inside the TEST square, SOLAR_IN test point?

author: psysc0rpi0n
author_rank: Frequent Contributor
timestamp: February 17, 2025, 04:04:36 pm
content: Quote from: Peabody on February 11, 2025, 11:33:02 pmYes, I identified pin4 of CN3165 and Source pin of Si2301 (A1SH ic on the board), and they both measure 4.30..V. I'm inside my office now with the panel at the window! Just to note!

author: Peabody
author_rank: Super Contributor
timestamp: February 17, 2025, 04:51:52 pm
content: If you have 4.35V at pin 4 of the CN3135, and the main circuit is switched off, then the battery should be charging if it needs to be charged. So either the "Charging" or the "Charged" LED should be on.In any case, it seems your solar panel is good, so if things still aren't right, it's not the panel's doing.

author: psysc0rpi0n
author_rank: Frequent Contributor
timestamp: February 17, 2025, 05:15:10 pm
content: Quote from: Peabody on February 17, 2025, 04:51:52 pmYeah, maybe inside the office the panel isn't getting the so needed sunlight to be able to deliver all it has to deliver. But even so, I don't know why the other day the battery I tried to charge, didn't go past 3V of charge!

author: Peabody
author_rank: Super Contributor
timestamp: February 17, 2025, 09:39:16 pm
content: Is it possible you didn't have the power switch turned off for the rest of the circuit?

author: psysc0rpi0n
author_rank: Frequent Contributor
timestamp: February 18, 2025, 11:51:29 am
content: Quote from: Peabody on February 17, 2025, 09:39:16 pmSince I started this thread, I'm pretty sure the switch has been always off!