SMPS for charging circuit readings wrong?

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bike4life   10 W

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SMPS for charging circuit readings wrong?

Post by bike4life » Jul 23 2021 1:51pm

i purchased a 1000W SMPS 120v AC --> 36V DC supply. This is for charging my ebike. I wired it up against the battery for charging and the following readings are done with a ac/dc clamp meter.

I am measuring 12 amps on the input and 27 amps on the output.

12 x 120 = 1440w.

36 x 27 = 1000w

roughly 70% efficient i guess. 1000/1440 = 70%

I am feeling the case and its cool too the touch, attached to the case i can see the screws which hold the mosfets / igbt which are heatsinked to the case and i can feel them and it feels like 10 watts, very low, yet i dont get why my readings say its losing 400 watts. I dont feel 400 watts of heat for sure. I dont think i am losing 400 watts from power factor as SMPS do not affect power factor.

comments????

This is for a special build where i need at least 95% efficiency. I feel like AC / DC current meters / clamp meters which i used are not accurate at all, and maybe i should go oldschool with a shunt.

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E-HP   100 MW

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Re: SMPS for charging circuit readings wrong?

Post by E-HP » Jul 23 2021 8:38pm

bike4life wrote:
Jul 23 2021 1:51pm


I am measuring 12 amps on the input and 27 amps on the output.

12 x 120 = 1440w.

36 x 27 = 1000w

roughly 70% efficient i guess. 1000/1440 = 70%
12 x 120 = 1440 VA, not watts.

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bike4life   10 W

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Re: SMPS for charging circuit readings wrong?

Post by bike4life » Jul 23 2021 11:04pm

they are =

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E-HP   100 MW

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Re: SMPS for charging circuit readings wrong?

Post by E-HP » Jul 23 2021 11:21pm

bike4life wrote:
Jul 23 2021 11:04pm
they are =
Only for a pure resistive load. The AC is providing power to the power supply, which is not a resistive load, therefore you have to take into account the power factor. Only a pure resistive load will have a power factor of unity.

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Chalo   100 GW

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Re: SMPS for charging circuit readings wrong?

Post by Chalo » Jul 24 2021 2:11am

bike4life wrote:
Jul 23 2021 1:51pm
This is for a special build where i need at least 95% efficiency.
Do you really? If so, why?
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

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bike4life   10 W

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Re: SMPS for charging circuit readings wrong?

Post by bike4life » Jul 24 2021 4:38am

E-HP wrote:
Jul 23 2021 11:21pm
bike4life wrote:
Jul 23 2021 11:04pm
they are =
Only for a pure resistive load. The AC is providing power to the power supply, which is not a resistive load, therefore you have to take into account the power factor. Only a pure resistive load will have a power factor of unity.
i thought only motors, capcitors, affect power factor, i thought SMPS's and fancy silicon is exempt.

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E-HP   100 MW

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Re: SMPS for charging circuit readings wrong?

Post by E-HP » Jul 24 2021 11:05am

bike4life wrote:
Jul 24 2021 4:38am
i thought only motors, capcitors, affect power factor, i thought SMPS's and fancy silicon is exempt.
I guess you should reconsider some of the reasons that you've already eliminated? The efficiency of a power supply is based on real power in vs real power out. By using the AC voltage and measured AC current to calculate "watts" for the input, you are assuming unity/PF=1. If you want to know real power in, use a wattmeter to measure the AC input, rather than using your clamp meter and calculating the apparent power in. They sell cheap watt meters in the big box stores if you are only dealing with house current/voltages. You could also get better instruments that will provide all of the values and are more versatile, but why spend the money since it doesn't seem like you're trying to solve a real issue.

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