I was playing on 1.6.4 DNSTechPack and used Electrolytic Separator with Hydrogen Generator.
The first consuming 200RF/t and second producing 2kRF/t if I remember well.

Now in 1.7.10 client with 7.1.0.94 mekanism, Electrolytic Separator consume 2kRF/t and Gaz Generator produce the same amount. So this setup cannot be used anymore to generate energy.

Bug or expected change?

Intended change. See #1037. Basically previous behaviour was in flagrant violation of conservation of energy.

You can alter the amount of energy needed to run the separator using the hydrogen energy density config option, but it will make the same difference to the hydrogen generator's output. In order to be energy-positive, you'll have to make ethylene in a pressurized reaction chamber which you can then burn in a gas-burning generator to get more energy out than you're putting in.

this is fine, but the generators dont really come anywhere near the ability to support their use at a game-playable rate without SCADS of solars and heat generators to support JUST ONE electrolytic separator. Now i know could go and CHANGE it, but out-of-the-box that makes things run far too slow.

@kotoroshinoto Really? With a bit of energy for a jump start, a single Gas Burner, burning Hydrogen, will run a Separator producing Oxygen, at half speed, indefinetly. If you set up a PRC, a small bank of Gas Burners (3/4) running on Ethylene, will achieve the same result with plenty of leftover Hydrogen.

I was getting crashes upon connecting any sort of hydrogen to a gas burner. Additionally, wasn't the Hydrogen production brought in-line with the cost of running an electrolytic separator? Maybe i'm running a beta or alpha version? the version is 7.1.1

That's exactly what I mean. A Gas Generator running on Hydrogen produces exactly the same amount of energy, as the a Separator needs to produce the same amount of Hydrogen. So a closed Hydrogen <-> Energy loop with a single Separator and a single Gas Generator will work forever, producing Oxygen, at half max speed.

Entropic effects demand that the closed loop you described earlier should not be infinitely sustainable (energy lost as sound, heat, other inefficiencies etc.), but if you're dead set on it, consider this: sodium reacts with water to produce sodium hydroxide and hydrogen gas. Might give a useful purpose to the sodium. I'm not sure if an existing block could support a 2 gas in (or maybe water as a fluid) and 2 gas out. sort of reaction, but its a possibility.

If the reasoning behind that change was the massive violation of conservation of energy, being able to perpetually run thie loop you describe is STILL a massive violation of conservation of energy.

In addition to that consideration, in terms of gameplay, literally the only time this loop works is for generating oxygen. IT does literally nothing to help processing brine Does splitting brine have a different RF cost? (as far as I can tell there is no use for sodium whatsoever, it just gets dumped.) We also need to produce extra hydrogen for use in making HCl. We're still at a significant energy deficit that requires quite a powerhouse of energy production to keep going at an appreciable rate. For early game partial speed and incompletely fed separators makes sense, but even for end-tier technology, the power requirements to run these things at full power are quite daft. I'm not saying that the burning of hydrogen should be left high and the sepators put low, but they're quite out of keeping with the power demands (or output) of just about anything else in the mod. (other than the hydrogen burners themselves, but as i've said that system should be continously losing energy, not a stable loop)

It also puts the solars and wind generators in the odd position of being absolutely DWARFED in power output despite being sorta expensive themselves.

True, but I consider the (indeed unphysical) assumption of perfect 100% efficient generators to require a significantly smaller suspension of disbelief re: conservation of energy than it being just flagrantly energy-positive. I would consider reducing the efficiency of Gas Burners slightly, but we already get complaints from people thinking they've been overly nerfed (see, well, this issue). If I did so, I'd probably make it so that energy loss happens at the same rate as the power produced by a basic Solar Generator or some other low-level generator.

I consider the base issue here to be balancing the default energy density of Hydrogen, which is configurable but should probably be lower by default (I already reduced it to match the old HG generation rate, maybe check to see if yours is still 2000? Should be 200).

I did originally have brine electrolysing to give 2H₂O + 2NaCl -> H₂ + Cl₂ (+ 2NaOH) (as these are the actual electrolysis products) and ignored the NaOH but that was changed at some point to produce sodium instead (@aidancbrady, should we think about changing it back?). We could alternatively use the Chemical Infuser to do 2Na + 2H₂O -> H₂ (+ 2NaOH).

mine does appear to still be 2000, might be due to the modpack authors not re-creating their configs from scratch after each update.

Did any other default values change recently?