DC-DC Step Down Converter Selection

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NiCat23

1 mW
Joined
Aug 8, 2019
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12
Hi, I'm planning on running two 2P10S battery packs in parallel. Each pack will have identical cells and its own BMS. Each pack will be charged separately.

I want to connect one of these ammeters (see link below) at the output of each battery pack to monitor the currents, ensuring they are similar. I will mount each display on the handlebars of my bike. The motor controller is set to draw a total of 15A so ideally, each pack will output 7.5A. The ammeters can read up to 10A so I think they are suitable.

https://www.aliexpress.com/item/32310008404.html

The ammeters require a voltage supply of 4-30V so I cannot provide this directly from my battery (cutoff range ~30-41V).
I don't want a separate power supply to power these cheap ammeters. I don't want to tap out of a 3S or 4S group of cells on one pack. Only other option I can think of is to use a DCDC step down converter.

I've had a look on Mouser, Ebay and somewhat reluctantly, AliExpress for DC-DC converters. I don't have any experience using DCDC converters so I'm a bit of a noob when selecting the right one. Here are some examples that I've considered.

https://m.aliexpress.com/item/33054259205.html?sellerAdminSeq=226886743&spm=a2g0n.search-amp.list.33054259205&aff_trace_key=22043cce436742dfa35e12a3d302d5de-1566158119908-04754-UneMJZVf&aff_platform=msite&m_page_id=1256amp-08GfH0xX6GcbuLEnOKnLXA1566159468714

https://www.ebay.co.uk/itm/VI-JN3-CW-36v-76v-In-24v-100W-Out-Isolated-DC-DC-Converter-VICOR/113847624322?hash=item1a81d8e282:g:9rAAAOSw~fFdTFyl

Are either of these any good/suitable? If not, can anyone suggest any better alternatives?

Thanks!
 
Is that a 2S10P OR 20S10P???

Yo, check this out:

https://www.ebay.com/itm/Pro-Chaser-DC-DC-48V-60V-72V-Converter-Regulator-Step-Down-to-12V-240W-20A/223130887152?_trkparms=ispr%3D1&hash=item33f3a323f0:g:fTcAAOSwLi1cm0HR:sc:USPSFirstClass!91910!US!-1&enc=AQAEAAAB8BPxNw%2BVj6nta7CKEs3N0qVGhotr6V6NZ2%2FXw0jJzbzv4xPYElGNFDIgaWv08tU3jj%2BgmftDVMcRxveZNr%2FMWyIc6gAhnaOHg%2FrFtGe24tI72K7AW3TEMwUDETvPd%2BiR%2Ba9CEdh4QwgGBDHdYNkDpYU6pZ8kiEAgxIP%2BEYMypwbc6jPcPacBpLqJURoUY9bQ4aZOEic5QLWC5hvRBrRtyH0%2BBXUIW%2FUDbQ1CqFupjlDIyxjgu0Jwa2tT2AgykXNgSTFg9eYU6N3IN032yJG5xlEmxQWar7Sz5xRPYNQTXuBXvRQZvQcbJGUV0jT54%2B8TnBqRaFUBWWWxOkzJiwxUGx6a4%2B3hwM2fvkrYRS4k%2B6Y7jxnLFiw3DGvSPmY%2Fhqw7viXQl3EJ2agIoYQ0O7Ht2q%2ByvLObSsJp99sRDfMGzuFUwE7BJDYMuXecuP6zEZI2FL5AmkRUR3i4X2cCp106FF%2Fj465eyNf7pMZYf%2Fy8Fouo5Gj%2BUsbhn0t4LvHWMm4H5oQvQCvYy%2BFsQAT1FkwP1o%2Fjzv12ShoN48%2FgMsSCODaiB1zLur0irmoaowl9Of9%2BCSLg5Ox38QpgJVV15wHtB40xtnMoKBE8tejWRhk9KVF2%2FePV0uCUPhUpZYoQ3KeQzcDG6DvyMyaLDThCCjCg2iU%3D&checksum=223130887152989e7ab905ed4883a675e546199bfbaa

And they offer a whole range of them (look in the item description).
 
Hi rockstar195.

I do mean 2P10S. From what I've read, 2P10S is slightly different from a BMS point of view to a 10S2P configuration. It's only a small battery setup I'm running.

It is my first ebike project so didn't want to go for a gigantic voltage and massive currents haha.

If you parallel two batteries which are each 2P10S, my understanding is that that effectively becomes 4P10S.
 
If it were me, I'd choose a different meter to avoid the problem (and complexity). You may also want to consider meters with external shunts. This would avoid the input supply issue as well as avoid having to pull heavier wires to your meters, since with your current meters, you need to pull 4 thicker wires from your batteries to the meters.
 
Hi E-HP,

Thanks for the advice!

Do you have any recommendations for other meters? My main criteria are small size and low(ish) cost as I just need an indication of the current flow from each battery. I'm also going to have a more sophisticated wattmeter to track Ah, Wh and Voltage of the overall battery so I don't want 3 huge panels on my bike.

Yes an external shunt makes a lot more sense for smaller wires. Would I be able to house it within one of my battery boxes and run the thin wires up to the display panel on my handlebars?
 
NiCat23 said:
Hi E-HP,

Thanks for the advice!

Do you have any recommendations for other meters?

Yes an external shunt makes a lot more sense for smaller wires. Would I be able to house it within one of my battery boxes and run the thin wires up to the display panel on my handlebars?
Click to expand...

Yes, the shunts can go anywhere closer to the batteries or controller. The one I was using also displayed watt hours, so was a little bugger than yours, but there are a lot to choose from.
I always try to consider my future upgrades so I don’t add to my parts box; so even if you don’t think you’ll run more power, you may consider that as well. I mention this because the shunts have current ratings and they can get big. You’ll be able to use small ones due to your modest power needs, however, you may want to plan for the future and get ones that will handle more.


Sent from my iPhone using Tapatalk
 
E-HP,

I had a look around this evening. Option one is a common RC car wattmeter with a shunt built into the casing. I've seen a thread about removing the shunt and relocating it externally which I'd be willing to give a shot at. Option 2 is smaller, but can measure less current (50A vs 130A). It also takes a supply voltage of up to 40V (I can live with 4V per cell) and comes with an external shunt.

With my current needs I'm tempted by option 2 but if I scale up my battery size in the future, I guess option 1 would be more suitable. If the shunts are external, is it not possible to 'beef them up' accordingly or am I talking nonsense?

https://www.ebay.com/p/High-Precision-G-t-power-RC-130a-Watt-Meter-and-Power-Analyzer-LCD-Gt-power-60v/509814120

https://www.amazon.com/Programmable-Voltage-Current-Energy-Forklift/dp/B01722SRTY

Thanks again.
 
NiCat23 said:
If the shunts are external, is it not possible to 'beef them up' accordingly or am I talking nonsense?
Click to expand...

Entirely possible, but the meter has to be able to calibrate to the new shunt value. For instance, the Cycle Analyst displays have a setting to adjust to the shunt you're using. I sort of doubt that the cheaper meters have that ability, but maybe they do. Option 2 sounds fine for now though, although it's creeping up in size. The one I have is like this one, that uses the battery voltage as the supply, so only 4 wires (two are common, so 3 wires minimum).
https://www.amazon.com/bayite-6-5-100V-Display-Multimeter-Voltmeter/dp/B013PKYILS/ref=pd_cp_60_3?pd_rd_w=EzfpW&pf_rd_p=ef4dc990-a9ca-4945-ae0b-f8d549198ed6&pf_rd_r=V4R3FT7749Z0VPG27RTX&pd_rd_r=3531cedd-f7e6-4980-819e-993d42f8ca94&pd_rd_wg=EaxTU&pd_rd_i=B013PKYILS&psc=1&refRID=V4R3FT7749Z0VPG27RTX
 
NiCat23 said:
The ammeters require a voltage supply of 4-30V so I cannot provide this directly from my battery (cutoff range ~30-41V)
Click to expand...
Step 1. order the Ah counters you want, all of the lower-voltage devices the bike will carry.

2. actually measure the power they require, the coulomb-counters' will be **miniscule** - recommending a 20A converter is ridonculous.

3. look on eBay for tiny form-factor converters that put out 50-200% more power than you need, widest range input, 12-14V output.

Even from top western makers from the industrial / telecom world:

Ericsson, Cosel, Tyco, Lucent, Delta, Alcatel, Astec, SynQor, ABB, GE, Lineage, Delta, Artesyn, Vicor, TDK, Lambda

will be cheap as chips, and **much** more robust and conservatively rated than any cheap-Chinese stuff sold new.

Used fine, NOS better, discontinued NP long as you can find the PDF specs and details.

Learn to decode proper datasheets that cover dozens of variants.

Do not buy units without that level of documentation.

Just a random example, overkill on quality, much pricier than required, google Vicor vi-200 series, VI-221 specifically

https://www.ebay.com/sch/i.html?_from=R40&_nkw=vi-221+vicor&_sop=15
 
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