I see what you mean now. LowZ injectors really are a pain in the arse So are engines with more than 4 cylinders haha. It seems that perhaps it will be more important to design a good heatsinking technique to suck out the 85W of heat generated rather than dicking around with a SMPS though. 85W is a huge amount to be dissipating in that form factor without fan forced cooling, or even any cooling fins. I certainly wouldn't want my ECU being too hot to touch even in a worst case scenario. I guess there's a plethora of ways to engineer around these issues, we just have to pick our battles. Researching a PWM p&h technique that doesn't swamp the rest of the circuit with noise may be a better option given that this is where most of the power dissipation will be coming from. Or just make everyone buy highZ injectorsjharvey wrote:The issue is that it's predicted to draw on the order of .25 amps to .5 amps under some fairly common built setups. So the regulator needs to drop (18v-5v).5A = 6.5 watts and we have been planning for 1 amp as extra room for growth isn't bad, so it could have to dissipate around 13 watts. With an ambient temp of 110F(43C) and LowZ injector drives in the case (estimated at 9 watts each for 8 cyl's), we are talking of a total case dissipation in the range of 78 watts to 85 watts for something the size of your hand. The internal component temperatures would likely be near the top range of their limits. So the LDO's temp compensation, and abilities to provide a 5V supply vs a 4.8V supply are likely degraded.
Thanks for your efforts to explain the engineering decisions that are being made by Marcos and yourself. I appreciate you bringing me up to speed. Marcos seems like a top guy. He's certainly put in a lot of effort thus far. His first attempt wasn't bad for a guy who's still at uni. I wouldn't mind giving my own FreeEMS board a shot at some stage. Board design is one of my stronger points of elec design. We'll see if I can maintain motivation for the project as we go forward.jharvey wrote:As a bit of a side note, Marco's first language is Spanish I believe, English is secondary. This is one reason why I'm doing a lot of commenting semi on his part. It takes him longer to type, and his goals are to make PUMA, and less to socialize in the forums. So chatting with me about design details will likely steer PUMA's design even though it's actually being laid out by Marco.
I have a similar qualification - a BE in mechatronics which is split pretty much 50/50 mechanical and electrical engineering. I agree that there's often a lack of communication between the elec and mech sides of a design. At least in my experience. Usually it's because the other team is always telling you can't do somethingjharvey wrote:As another side note, I have a BS in Electro-Mechanical Engineering. I tend to jump electrical and mechanical bounds on a daily basis. It's common that electrical's will design something, then the mechanicals will make it work. I tend to look at the entire picture a bit more than most typical design builds. It's likely that mechanical issues or obstacle are semi hidden from the electrical designer. In a typical design cycle.
Phew that was a marathon reply...