Adding a battery in parallel

Esk8 Electronics
#21

These are the ideal diodes I have:

Specs say upto 70vDC, and 0.04v drop at a 28.6 amp load.

I will measure the drop across them next time I drag my gc-2 AGMs down low enough they can take ~50 amps.

I misremembered the flow on the 3s packs, I was trying to drain my ~12.2v 3s Lipo weld battery down, connecting it to my 3s1p 18650 pack that was likely much lower, and saw 12+ amps flowing through my wattmeter, and decided that was way too much.

…
Maybee the ideal diode can be used to charge one battery from the other more safely than putting two in parallel.

#22

They’re lying about the voltage drop.
That FET has about a 9mOhm Rds-on when hot and that gives you a voltage drop over six times higher than they say, about 0.26V. And that’s only the FETs Rds-on. You have to add on the other resistances from the soldering, PCB copper, and terminal.

It’s a 150V FET so the 70V rating probably comes from a 75V ideal diode controller that’s running the show. They scratched off the number in that eBay listing but perhaps it’s visible on your unit. It’s the small chip to the side.

1 Like
#23

Yes, that is the ebay doohickey I got.

#24

The number was scratched off on mine too.

Im gonna go load my 12v agms so they can accept 40 + amps and will test actual voltage drop across it. I did it when I first got them, and was satisfied, but forget the actual numbers.

I primarily use them on my 100 amp power adjustable voltage power supply, so when i turn off the AC switch, I dont have to disconnect the DC connectors from battery to shut off my additional fans

1 Like
#25

tenor (1)

1 Like
#26

me, has 6 packs in parallel :disguised_face:

#27

Ok, some data, as promised.

I drained my 2 GC-2 6v agms in series for 12v nominal, till they were 12.02v.

I turned on my 100 amp adjustable voltage power supply, jammed my dmm probes through repurposed wattmeter housing, onto main Ideal Diode terminals.

No load voltage drop across terminals
@12.2v…0.033v
I dialed up voltage
0.039v at 5.9 amps
0.05v @29.9amps
0.098@53.5 amps and 14.2v

My diodes are wired with 8mm2 and 8awg across 45 amp anderson powerpoles on either end, and are warming up rapidly at this point

Holding 14.2v on power supply output…
0.104v drop at 51.8 amps
0.106@ 50.3
0.108@ 50.7
0.114@50.4 amps.

At this point I connected my second set of 8 awg 45 amp powerpoles across second ideal diode and ammeter on powersupply jumped to 60.1 amps.

I started typing the above, fat fingering at 7 beers deep, this data.

shunted ammeter on power supply output says 57.4 amps @14.2v

The original ideal diode and wiring is now hot as fvck
clampmeter over it says 29 amps
voltmeter says 0.055 volts drop across terminals.

second diode says 26.62amps.
lemme puncture housing to read voltage drop across ideal diode on cooler diode…

0.040v

I wish I had a second set of hands and eyes to help take photos.

this is the original hotter one:

20240201_225455
20240201_2254551920×1080 136 KB

20240201_225552
20240201_2255521920×1080 121 KB

In the process of loading my agms, i charged my new 10s 2p battery through a booster upto 42v.

I will stop charging the agms , wbich are still taking 42.5 amps at 14.2v now, Ill use a CCCV buck converter from 10s battery, through ideaL diode toncharge agms, and taKe data.

2 Likes
#28

Ok.
There will be no ideal diode voltage drop data at 42vDC input

Some idiot decided not to notice that they’d wired up both input and output sides of their buck converter, with fuses, and the sexless anderson powerpole connectors allowed them to far too easily, hook it up backwards.

POP, went something on bucker, a split second before the external fuse popped on what was supposed to be the input side, but was unfortunately the ouput side.

It now has that distinctive magic smoke escaped smell, but at least i have two nice finned heatsinks i get to repurpose.

My new 10s Battery is now sitting at 41.97v, and i have no way to discharge it, other than to skip the enclosure BS, duck tape it and 10s ESC to my board, and have at it.

1 Like
#29

My first long distance esk8 was on a shoddy evolve GT, with a 10S9P battery chucked in, using techniques I’m not proud of. 1kwh was enough to keep the thane rolling around the city streets, but…

One Friday night I had decided to skate inland about 80km to a campground, and the 97’s weren’t the fastest rolling on the course chip and gravel roads, So I decided to spend three hours formulating a solution.

Having purchased 100 x10s3p lime (public) scooter batteries used from a recycler, I selected five of the most charged packs and ensured they were all at the same SOC - 41V approx. A header made from a bunch of XT60 plugs, A D20 MCB, and some speaker cable long enough to reach from a tramping pack and down each leg of my jeans was sufficient to crimp onto copper plates cut from my previous copper hot water cylinder I had recently replaced. Each pack had an integrated BMS.

I nut and bolted the plates to the soles of my shoes, and did the same to the deck of the GT, using the enclosure screws as conductors, with copper lugs beneath the deck. I added a 30 amp automotive fuse to protect the plates, should my board flip and land upside down on a cattle stop or something.

Parallel batteries have given me a great memory, and earnt myself a name of Dorothy with some, after having electric shoes like in the wizard of Oz. Given it was winter, and heading inland as far as I had, in the cold - the electrical risk of my decisions was the least of concerns. My hands were too cold to use a phone, and it was close to freezing. The evolve GT remote began to go flat, and I had forgot the USB cable. The gravel roads were like river stones, and I was in a frame of mind more suited to attending a techno music rave.

I don’t disagree with the others who might recommend DC-DC converters for the load, if correctly selected and implemented these could make for a safer, more fool proof design. For my own use, I would feel comfortable making a basic and simple range extender pack but I would be VERY mindful of the SOC of both board and pack when connecting them. It wouldn’t be something I would lend to a friend this way.

#30

What FET is on your diode boards?
Your (very low) 114mV drop at 50.4A = 2.3mOhm resistance and the FET in the eBay photos you linked to (and that I based my calculations on) has a much higher resistance.

I’m wondering if those eBay photos were of an earlier prototype they had and not what they’re shipping?

1 Like
#31

I bought those ideal diodes at least 3 years ago, I am not sure whether from Amazon or Ebay. I briefly searched my ebay purchases and nothing hit, so then just searched ebay till I saw a pic that looked like what I have, and linked that.

I do recall when I got my first one, not reading the directions, seeing that there needs to be a negative lead on the board, and was seeing 0.4drop across it unloaded, and no one way valve action, contacting the seller, who was like dumb American, please to follow directions on photo.

Before they replied, the guy who recommended them to me, who also didnt read directions, was fuming cause he thought their effort to wipe the info from the components, static-ly smoked them in the process.

When I did read directions and wired accordingly, and saw it performed as advertised I apologized, and recommended he put the directions product description, not in a photo, and ordered two more.

One is on the output of my Meanwell rsp-500-15, two others pare portable, inside wattmeter housings, one of them has now a big copper heatsink stuck atop the main FET in between terminals, the other does not.

I just keep them on my 100amp powermax adjustable voltage power supply outputs, so i do not need to unplug the DC connectors when I turn it off and reattach when I turn it back on. Very convenient. Their low voltage drop not really needed as I could just dial the supplies’ output voltage higher to compensate.

All three ideal diodes have seen a lot.of use, Glad I have them.

I can take the other one’s casing apart and try and read anything visible on the components, a bit later today, but IIRC, the seller or their parts provider decided that info was not to be shared and scraped their surfaces clean of parts numbers.

#32

20240202_124057
20240202_1240571920×1080 210 KB

20240202_124028
20240202_1240281920×1080 213 KB

They scraped off the part numbers on the little chip

1 Like
#33

Thanks!
That’s the same FET as in the eBay photos. Its resistance spec should result in a much higher voltage drop than you measured for that current level but I’m glad it hasn’t!

1 Like
#34

I’m glad too.
Ignorance of the FET’s resistance spec was bliss.

I’ve been taking these ideal diodes for granted.
3 have basically in continuous use for years now.

#35

I bought another ideal diode, well, I bought two.

The first one, purple, has a no voltage limit, just not allowed higher than 40v difference.

I could have screwed it up wiring it incorrectly originally, like a dumbass, but its voltage drop when wired correctly, is inconsistent, rising from 0.04 to 0.4v, cycling over and over every 5 seconds or so.

So I bought another red one like pictured above, that I’ve been using for years.

This newly arrived one, they didn’t bother obscuring the markings on the little processor like they did on my other two.

I’ve not tested it yet.

20240406_161244
20240406_1612441920×1080 182 KB

2 Likes