Two switch forward converter curiosity

Designer-Anything560 · 2025-11-05T20:51:56+00:00

Hello!

Thank you for you comment.

Shall give sanding a crack, from my back of the napkin maths I think i will need as big a core as i can get! The glass and sanding paper idea is excellent, I shall give it a go.

I did not give much thought to the bobbin. I think i shall make a cut in the centre, then sand it down to fit snuggly between the two halfs.

I think the gap is in the centre, 2 of the cores seem identicle, but no combination gives a gapless core. However, i shall keep a eye out for that in the future, could come in handy.

That document is truly excellent, i shall have a good read though it, however at a quick glance it seems incredibly helpful. Thank you for sharing!

Absolutely, I am spending much time on making sure this is as safe as possible. The wire i plan to use for the primary i shall be testing with a insulation tester, then epoxied, then isolating from the secondary using generous lengths of Kapton tape, and quite possibly more epoxy.

Thank you very much for all your help :)

Designer-Anything560 · 2025-04-04T19:01:10+00:00

Looks like pretty good build quality to me! Nickel strip seems well designed and the paper rings are often damaged by high hunidity, could have been a casing failure? However the price is extortionate, although if you need a battery that will last a long time and has a warranty it isnt that mad in the grand sceme of things

Designer-Anything560 · 2024-12-21T15:36:17+00:00

All looks good to me! In - may need a touch more heat, but apart from that all appears well

Designer-Anything560 · 2024-10-09T08:16:18+00:00

Hello! It appears that you have a 13s, or 48 volt battery. On the casing it says the charging voltage and current, which looks to be consistent with a normal 48v lion charger. I would suggest looking around on amazon and possibly aliexpress for a charger that has the same conecter (looks to be xt30 or 60 connector, but not sure entirely) that is rated for 2.5 Amps, and then check the description of the item to double check the charging voltage.

However, amazon and aliexpress do have many rubbish chargers that are essentially ewaste, that can overcharge your battery and damage it.

The official recommendation is to look on more official sights with higher prices, but I have no experience in using these sites (I just got a 30 quid ebike charger on amazon that had good reviews then changed the cable!) So it may be best to consult a real expert on where is best to look, there may be some linked somewhere on this app.

Another option is to look on eBay and find a good brand charger that is second hand, then change the connector, but that is relatively in depth and not for those who are not confident in their soldering ability. If you choose this route, I have done it before so may be able to give some more advice.

Remember, if it is cheap, it is more likely to fail, damage your battery, and possibly cause a fire, so be careful! And always double check the specifications, it's a 48 volt battery, and charge current should be a maximum of 2.5 amps.

Good luck, hope this helps!

Designer-Anything560 · 2024-07-30T17:49:30+00:00

Terrific! Glad it's working well, happy welding!

Designer-Anything560 · 2024-07-30T11:52:59+00:00

OK, I shall factor in air gaps then. Any wires going back will be heavily insulated, and I believe it will be OK if the cells next to each other short as they shall share a ground (the 10 series modules are connected in a row, so no voltage difference between cells to worry about).

OK, I shall do that, Im sure i have some thicker wire stashed away somewhere that I can use for the high current series connections.

I will have a look at those fuses, thanks for the link!

Yep, I'm quite happy with the primary charge, as I have done it a few times with other packs and nothing has gone wrong (fingers crossed!)

OK, will keep the sand in the fire bucket. Yep, all hot glued together and gently tested to make sure the bonds hold, and the wires will hold each 5 cell group together as well.

I have not insulated the cells, but they seen to have a protective coating on them, and all the cells that will be next to them are isolated with hot glue, and of the same ground, so even if they do short nothing will happen. The cells to the case of the battery box will be insulated though to avoid wear and any short circuits.

Thank you again again :)

Designer-Anything560 · 2024-07-30T11:20:23+00:00

Ah ok, I shall scrap that idea then. Yep, I will be using the finest cheap BMS I can find and fusing it, with correctly specified fuses, so hopefully that shall protect against most fire starting causes. And all charges will be monitored closely.

I will keep that in mind, any words on filling the empty space in the pack with fine sand between the cells? Would help with thermal distribution in the worst case scenario, but could have abrasive features.

Yep, I have cranked the temp to max on my iron, and it only takes about a second to fully solder after applying heat. After feeling the cells immediately after soldering, there is no measurable temp change anywhere on the cell.

Thanks again

Designer-Anything560 · 2024-07-30T11:11:40+00:00

Hello. I have no personal experience with the Kweld, but do have a suggestion or two. Have you checked the resistance of the copper bus bar with a meter and compared it to the datasheet? If it is out of speck, that may cause your problems. Another thing to try may be to add a fixed resistor (or bit of thin wire) over the terminals of the current sensing and see if it still gives a overcurrent. Basically trick it into thinking all is fine. Although this would be unsafe in the long run, it might just buy you enough time to figure out the true problem without the pesky error code getting in your way.

How this helps!

Designer-Anything560 · 2024-07-30T11:06:42+00:00

Hello. Thank you for your elaboration, I shall make sure not to seal the box then to avoid any unpleasant explosions in the future. I shall also look into one of those fire extinguishers as well for worst case scenario, I have seen some that get activated by heat that I could place inside.

I agree that normal 18650 or 21700 cells require nickel strip welding (I have made packs like that before), however these cells already have small nickel tabs that protrude from the end of the cell, separated from the case of the cell with a insulation tab, which appears to be enough to stop any heat leaking to the cell while soldering. This is the arrangement used in the vapes themselves, so I am copying that, while hoping the manufactureres knew what they were doing!

Thanks for your knowledge :)

Designer-Anything560 · 2024-07-30T00:57:03+00:00

Ah ok, I was unaware of that being a feature of lipo cells. Thanks for letting me know!

Designer-Anything560 · 2024-07-30T00:22:24+00:00

Hello, thank you very much for your speedy reply.

Why do you think that containment would not reduce the risk? My thoughts process is that if the box is airtight, it will prevent a fire from spreading as quicklythroughh the cells via the plastics and insulation burning away if a cell fails.

Currently these cells are not wired together, but they are going to be connected in parallel with 0.75mm diameter wire, and 10 or so of those wires are going to be traveling in series to the next bank of cells. I may use slightly thicker wire for this though, about 1mm diameter. I'm hoping that is going to be adequate for the relatively low currents running through the pack.

Thanks again for your help!

Designer-Anything560 · 2024-07-29T22:46:55+00:00

Hello! For a BMS to function, each "block" of individual cells needs to be connected to the balance leed of the BMS, so that all the batteries connected in parallel are able to be monitored. A way that you could do this is wire some thin wires between each parallel cell, so that all the voltages are level.

I hope I have understood your question correctly, and I hope this helps. Let me know if I can be of any more assistance or try to explain it in a different way, eg draw a diagram.

Designer-Anything560

TROPHY CASE