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I read from different posts the limit is 4, if you put more the motherboard cannot supply enough energy.

But I read also about rigs having 6 without issues for years.

Is that why i am asking which is the real limit ?

I am asking because I wish to make a new rig with both powered and unpowered risers but I need to know how much unpowered can be use safely?

It would depend on your mobo and GPUs. If your going to setup a rig, just get powered risers and be done with it. And I have run 2 GPUs on empowered risers no problem .

Back in the early days of BTC GPU mining the cards drew almost all their power through the PCIe connectors with exception of the low powered cards which drew their power from the PCIe bus. That bus is spec'd to provide up to 75W over all the slots. This is why you can run a 1050Ti without a PCIe connector - it typically shouldn't need more than 75W.

The problem comes from cards that now rely on the bus power. RX 470s, for example, were pulling a lot and were burning out some motherboards since just one card was pulling up to 60W sometimes.

Unless you're willing to clamp and measure the power pull of each card, just go with powered risers unless you want to RMA your motherboard.

Is there any tutorial to know with tester, how much energy required and how much the motherboard can give?

I use 1070ti at 60TDP, maybe no need of powered riser.

I use powered riser even with RX550 (50W TDP).