Questions regarding battery type and what voltage moving forward

[bcroe]

Do you mind explaining why this is incorrect?

This is how I am understanding it. These are P channel mosfets. If there is a positive voltage (12V+ in my case) at the Source (Left side of schematic) and 0v (GND) at the Gates that are tied together, This would allow current to flow across the source and drain to the output side.

Thanks!

Why would you need 2 MOSFETs in series to your Primary Output?
Bruce Roe

[georgia088]

Why would you need 2 MOSFETs in series to your Primary Output?
Bruce Roe

I have two different inputs. One is coming from a 12v battery and the other from a 24v battery. At the point of the input, they are both 12v. I am controlling which input is supplying the power with relays. However, in order to make sure that in a failure situation, the two do not become in parallel with one another, I am using the 4 mosfets as a safety (should really never matter unless a relay failed closed or some other failure) to make sure that neither input is “on” at the same.

The way I have it figured let’s assume the relays don’t exist and there is constant power from both sources going in to the inputs:

Looking at my diagram, the top input is the primary input. If there is 12v+ going to the source pin of the top left mosfet and there is a pull down resistor connected to the gates of both the top mosfets, current should flow across the source/drains of the top two mosfets. There should be no current flowing across the bottom two mosfets from the secondary source because the 12v+ from the primary source is feeding the gates of the bottom two mosfets so they are “off”. Which prevents any problems from occurring if both sources are ever on.

Now, if the power from the primary input is off, and the secondary input is on, the bottom two mosfet gates are no longer receiving 12v+ from the primary input and are being pulled Low from the resistor so the gates are low and the source is high, allowing current to travel across the drain/source of the bottom two mosfets to the output. Now that there is 12v+ going across the drain/source of the bottom two mosfets, the gates of the top two mosfets are connected to 12v+. This should prevent current from flowing back across the drain/source of the top two mosfets.

Does that make any sense?

Thanks!

[bcroe]

I still do not see what the purpose of having the 2 upper MOSFETs
in series. If you turned around the S and D on one, you could block
in both directions. Bruce Roe

[georgia088]

I still do not see what the purpose of having the 2 upper MOSFETs
in series. If you turned around the S and D on one, you could block
in both directions. Bruce Roe

And connect the secondary source to what?

[bcroe]

And connect the secondary source to what?

I did not say anything about changing connection to the secondary source.
Bruce Roe

[georgia088]

Well, I don’t understand. The secondary is connected to the lower set of mosfets and the primary is connected to the top. So, are you saying there should be 2 or 4 mosfets.

[georgia088]

I did not say anything about changing connection to the secondary source.
Bruce Roe

I thought the concern was the gates being in parallel.

[bcroe]

Why 2 in series?

[georgia088]

Why 2 in series?

From what I understand, a single p mosfet or p mosfets in parallel have a body diode, but when the mosfet is “on” they will allow current to flow in either direction across the drain/source. Because current can flow in either direction when they are “on”, I think this is a problem because when the other two mosfets are “off”, they will allow current to flow in one direction and this could possibly short at the junction or allow one input to back feed to the other input source.

Thanks!

[bcroe]

You still did not answer the question, and since I think you cannot,
I will not ask any more. Bruce Roe

[georgia088]

You still did not answer the question, and since I think you cannot,
I will not ask any more. Bruce Roe

First of all, I’m not sure who pissed in your cereal, but you have been zero help! On a forum designed to help and increase knowledge, you have done neither. Your only objective has been to TRY and make me look as if I don’t know what I’m doing.

Can you explain why what I have proposed won’t work, NO!

Have you offered a better alternative, NO!

Could I be wrong, sure? But, IF I am, you obviously don’t have the ability to explain why or offer a better solution. Therefore, why comment?

As to your last comment, I did answer your question. The question was “Why 2 in series?”

THE MOSFETS WILL NOT BLOCK CURRENT FROM ONE INPUT FROM BACKFEEDING THE OTHER INPUT OR SHORT CIRCUITING IF THEY ARE NOT IN SERIES AS MY SCHEMATIC SHOWS. AS A STAND ALONE MOSFET OR WIRED IN PARALLEL, THERE IS NO WAY TO CONFIGURE THEM TO PREVENT THE BACKFEEDING OR SHORT CIRCUITING.

Do you have a schematic where they are not in series and they work as I intend? If so, I have been begging you to provide it and an explanation of how it will do what I am trying to do. If you do, and there is a reason it is better than what I am attempting, I’ll be glad to use it. But, you’ve yet to provide anything useful.

I did not come here to argue or attempt to prove that you don’t know what you are talking about, but you obviously did. However, your lack of ability to provide any meaningful or useful information to accomplish your objective has not helped your case.

Please explain how the circuit will work without the mosfets being in series.

Or

Please provide a better alternative.

But, casting stones with nothing to back it up with is useless to me or anyone else that ever reads this. I hope you and everyone else has a wonderful Easter!

Thanks!

[sdold]

PCBWAY, etc. Do you solder your own, or do you use the SMD Assembly/PNP services that they offer? I have made a few, but I always used through hole components and hand soldered them. However, I am liking the idea of having them solder the majority of the components. I am just having a hard time finding the parts in their library (I use JLCPCB).

I recently used pcbway because it was easy to order using the PCB software (Diptrace). No need for generating Gerber files, you just click a few boxes. I was happy with the quality and speed of delivery. Anyway I've started using surface mount parts for most of my projects and couldn't be happier. I bought a $100 hot air tool and am amazed at how easy and fast it is to remove and replace parts to try different values or replace bad ones compared to de-soldering through-hole parts. Even ICs with small, closely-spaced pins are no problem. I use a syringe to put down the paste, set the part down, and heat it up on a hot plate or cheap convection oven and it just solders itself. I'm 62 and my eyes aren't the greatest, but I still have no problem. Just my experience, SMD doesn't mean you must have the board loaded for you (but if they can load some or all of them, it will make your project easier).

[venquessa]

I would suggest, especially with mosfets to start a thread on an electronics forum.

Beware of the body diode.

On PCBs. I use KiCAD. PCBWay or AllPCB, depending on which one has the cheaper "fast" shipping. Takes about a week. PCBs... £7. Shipping £35.

I agree surface mount is a lot less scary than you think it will be. Just get good magnification and VERY bright lightening. As bright as you can stand without getting a headache. You can pick up cheap microscopes for £30. I would recommend, considering going to one that at least has it's own screen etc, ideally an HDMI output. ~£120.

Hot air can be awesome, definitely worth it for a whole board with dozens of parts. You can also use the iron and a nice flat tip and for some chips it's faster than air. I especially found soldering an ESP32 wifi daughter card to a PCB was a pain in the butt with air. Far too much mass. The iron filled all those little castlated contacts perfectly in a quarter the time.

I also use a syringe and paste. I am however buying one of the pump handles for it as that stuff takes a LOT of force to get moving out the needle.

If the board gets beyond about 20-30 components I'll fork out the £10 for the stensil next time. Putting down the paste is nearly as fiddly as placing the components.

Heres a video I made when I was learning how to do surface mount ICs. The magic is in how the solar paste flows onto the chip legs itself, like magic!

https://www.youtube.com/watch?v=rgcupYOnvBo

[Calsun]

Remember that a 4S LFP pack with a durable BMS system will happily get treated like lead acid in 99% of cases. Niether load or charger should care it's LFP.

That is not true. The charge controller profile should support the battery type being charged. Maximum charging voltages and end point for a charge cycle will vary considerably between lead acid and lithium type batteries.

With my RV the use of lithium-phosphate batteries cut my charge times from the solar panels by more than 30% compared to the original lead acid batteries. But this required a charge controller with a charge profile for this type of battery.

[georgia088]

I recently used pcbway because it was easy to order using the PCB software (Diptrace). No need for generating Gerber files, you just click a few boxes. I was happy with the quality and speed of delivery. Anyway I've started using surface mount parts for most of my projects and couldn't be happier. I bought a $100 hot air tool and am amazed at how easy and fast it is to remove and replace parts to try different values or replace bad ones compared to de-soldering through-hole parts. Even ICs with small, closely-spaced pins are no problem. I use a syringe to put down the paste, set the part down, and heat it up on a hot plate or cheap convection oven and it just solders itself. I'm 62 and my eyes aren't the greatest, but I still have no problem. Just my experience, SMD doesn't mean you must have the board loaded for you (but if they can load some or all of them, it will make your project easier).

Hmm. Ok. I will check out pcbway. There was a pretty steep learning curve for the electronics design portion of fusion 360 (formerly eagle), and I was already an average user of fusion for 3D design. However, now that I am familiar with it (still no expert) I’m scared to change to different software.

The problem I am running in to now is finding the PCB components that the PCB manufacturers have in stock and using that components package/footprint to design my board. The board layout is obviously a lot different if using the smd components vs through hole. So, since before, I haven’t felt confident soldering smd components, I wouldn’t design my PCB with them. However, since reading y’all’s advice about using the hot air, I may give it a shot. I’ll have to check in to the microscope and hot air. I’m sure the Mrs. wont mind if I get a new toy…

JLCPCB really pushes easyEDA software and I think it includes the library with their list of available parts. However, it would be another software I’d have to learn. I wish there was a PCB manufacturer that had a library to add to fusion that I could use for basic components that they had in stock, but I’ve yet to find one. As venquessa said, I’m willing to pay a little extra for the PCB to be assembled or at least most of it on the more complex boards. I appreciate the advice/help!

thanks!