am i understanding this amplifier module correctly? - Page 1
Forum section: electronics / beginners

author: altruan23
author_rank: Contributor
timestamp: November 06, 2022, 08:22:04 am
content: Hello. So I want to drive a Peltier Module which needs 12V and 6A. My PLC can give me on the analog output maximum 10V. So basically I need a converter,which will linearly convert the 0-10V into 0-12V and provide 6A, my PLC can only provide maybe 20mA maybe a bt more but not even close to the 6A.I found this amplifier:https://www.joom.com/en/products/1522062941592548469-218-1-26193-3083599015When you look at the pictures, there is a picture on how you need to wire this thing. I see in the specs that you need to input your signal voltage from 0-5V which is ok,because my PLC can give 0-10V so I will just use a voltage divider. But the module also wants a supply power from 5-24V and it will provide an output signal which can be between 0-10V or 0-12V or 0-24V and 10A.My questions are: Do I need to provide him the power 5V and 10A? Or will he generate the 10A just from the 5V from power? I have a laptop cable which can provide 12V and 6A, so will this power be enough for him, that he will convert my input signal 0-5V into output signal 0-12V and 6A? It is also mentioning a PWM, i suppose it is an output PWM but I dont have any problems with it, my peltier will be able to operate with PWM. Please dont be angry if these are stupid questions, I am just a beginner.

author: pcprogrammer
author_rank: Super Contributor
timestamp: November 06, 2022, 09:06:40 am
content: Not a stupid question at all.The description on the site you refer to is not to clear, and my understanding is that you have to supply the working voltage, and that it needs to be in the range you want for your output. So for the 0-10V you would have to supply at least 10V, but probably more. The working supply also has to be able to deliver the needed current.The input signal will be amplified to the range of the supplied working voltage. The fact that it can do PWM probably means that you can put a PWM signal on the input and the output will switch in the same way, but at the higher voltage.Did not check the pictures on what components are used, but that can also give you clues about the working. For instance, get the part name of the big chip and search for the data sheet.

author: wasedadoc
author_rank: Super Contributor
timestamp: November 06, 2022, 03:38:33 pm
content: That module is not an amplifier. It is also not a voltage converter in the usually accepted sense of that term.It is a PWM switch. The component LR7843 is a MOSFET and is used as a switch between the negative of the power input and the negative of the power output. The switch is turned on and off at high speed. The ratio of on time to off time depends on the voltage input at the other end of the module. That means you can vary the average voltage at the output. The peak output voltage is not changed. If you apply 12 volts as power input, the power output is continuously switching rapidly from 0 volts to 12 volts to 0 volts to 12 volts and so on.

author: altruan23
author_rank: Contributor
timestamp: November 06, 2022, 05:37:03 pm
content: Thank you very very much for both replies and nice explenation. The perfect module for what I need, couldnt be happier.

author: Ian.M
author_rank: Super Contributor
timestamp: November 06, 2022, 06:20:39 pm
content: However, driving a Peltier module with unfiltered PWM is *NOT* recommended, as it typically causes around a 30% loss of cooling performance over well smoothed DC at the same average current, due to the much higher I2R losses.Seehttps://www.meerstetter.ch/customer-center/compendium/71-peltier-element-efficiency#DCvsPWMandhttps://www.ti.com/lit/an/slua979a/slua979a.pdfAs your proposed module from joom.com doesn't have any noticeable inductors on its PCB, its impossible for it to offer a filtered (smoothed) output at the current it claims to be capable of so it must output raw PWM. From the connections and components visible, it appears to be a PWMed MOSFET low side switch. As a minimum, you'd need a large choke in series with the Peltier module, rated to carry the max. load current without saturating, + a beefy Schottky diode across the module's Out+ and Out- terminals, cathode positive, rated to carry the max load current, to allow it to recirculate through the choke and Peltier while the MOSFET is off. The choke should be sized so the current doesn't drop more than 10% during the MOSFET off time. Without knowing the PWM frequency and min. duty cycle, we cant specify the choke.

author: EPAIII
author_rank: Super Contributor
timestamp: November 07, 2022, 09:33:27 am
content: If it needs 6 Amps at 12 Volts, just buy a 12 Volt, 6 Amp power supply.DONE!

author: wasedadoc
author_rank: Super Contributor
timestamp: November 07, 2022, 09:38:25 am
content: Quote from: EPAIII on November 07, 2022, 09:33:27 amMy understanding of the first post is that variable control is required. Also, the first post states that a laptop supply that can provide 12v 6A is already to hand so why buy another one?

author: altruan23
author_rank: Contributor
timestamp: December 19, 2022, 08:52:27 am
content: Hello. I measured yesterday the PWM frequency an it is 66-67Hz, it doesn't go higher than 67Hz. The peltier isn't working the way I wished. Would a diode and an inductor help? If yes, how can I choose the right one? The maximum output voltage is 12V, the output current can't go above 6A.

author: jonpaul
author_rank: Super Contributor
timestamp: December 19, 2022, 09:10:14 am
content: get a lab or OEM PS with filtered DC output, many have external R or V control.common industry commodityj

author: Ian.M
author_rank: Super Contributor
timestamp: December 19, 2022, 09:37:58 am
content: You'd need around 80 Henries of inductance to smooth the output of that PWM module. This is obviously impractical, as it would be far far more expensive and much larger than a module with a smoothed output operating at a much higher PWM frequency.Aside from Jonpaul's suggestion, if you are trying to do this on a limited budget, another option would be to hack a high current DC-DC buck converter module, connected between your 12V PSU and the Peltier element, by injecting a small current at its feedback pin to offset the output voltage. This could be as simple as a carefully chosen resistor between its feedback pin and the 0-10V control voltage, which would lower the output voltage as the control voltage is increased.

author: RoGeorge
author_rank: Super Contributor
timestamp: December 19, 2022, 09:44:08 am
content: Peltier elements does not work well with PWM. You need to use smooth DC, not pulses.

author: MathWizard
author_rank: Super Contributor
timestamp: December 24, 2022, 06:11:34 pm
content: Quote from: Ian.M on December 19, 2022, 09:37:58 amA small desktop ATX powersupply, like 350W, 450W, would put out 12V at 6A , work fine, and only wish the current was higher. Aside from that, a lot of them still run at a mainly fixed 50-100kHzBut yeah a used 450W ATX PSU should be pretty cheap, (there's a lot of junk ones though too).But for something can can do 12V and way over 6A, and for resistive/capactive loads, I'd try that.But yeah IDK how that gets regulated like the OP wants from the control signal.