EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: grandaspanna on December 07, 2023, 11:57:53 pm
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In the RC community, quite a few people build/run dynos to get load characteristics of brushless motors. It's common to use a 2S (two lithium cells in series) to power the speed controller driving the motor.
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Briefly, the problem is that voltage drops fairly quickly as capacity is used, making results hard to compare.
I'm exploring how to get a power supply that can deliver 8.4V +/- a few % at up to 60A. Input could be mains power (110 or 220 etc AC) or a bigger battery pack (eg: 4S lithium pack)
- I could build a DC/DC one from scratch, but handling 60A of current on a PCB becomes expensive (in small volumes) if I've done the calculations right
- Server PSUs typically have 5V output, but have power in the ballpark. Can they be adapted/adjusted to 8.4V?
Any other ideas or tips?
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I'd try lowering the 12V output instead!
The HSTNS-PL11 will be more than enough:
(https://a.d-cd.net/SZAAAgO2M-A-960.jpg)
Modification thread:
https://www.eevblog.com/forum/projects/hp-hstns-pl11-over-voltage-protection-voltage-increase/ (https://www.eevblog.com/forum/projects/hp-hstns-pl11-over-voltage-protection-voltage-increase/)
Github repo with Server PSU hacks:
https://github.com/darwinbeing/HPServerPSUHack/ (https://github.com/darwinbeing/HPServerPSUHack/)
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- Server PSUs typically have 5V output, but have power in the ballpark. Can they be adapted/adjusted to 8.4V?
Adjusted, no.
But you might consider using 5.0 V and 3.3 V server power supplies with the outputs in series. 5 V isn't too common these days, but look around.
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8.4V is an odd voltage for powersupplys.
It would be better if you can do it at 5V or 12V.
Most metal frame PSUs have a pot you can adjust located around the input terminals, so you could get the 5V up to like 6V, maybe 6.5V.
Maybe look for a 9V one and then turn it down to 8.4V, that's probably a better plan if you can find a 9V one.
Probably have to pay around AUD$100 for one that can do 500W
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What's wrong with a (PMDC) ESC? Preferably voltage programmable. That's just a buck converter with voltage regulation (and presumably
soft startacceleration and torque controlprogrammable current limiting), possibly ready-to-go.
You can get a buck converter for that level, but it'll be pretty beefy (or, those junk modules, pretty sketch), or a bit tricky to make from scratch.
Like, I have a few things on hand that can do that, but, they're not exactly products, and it's not economical for me to try and sell them, sadly.
Tim
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8.4V is what the ESC accepts, so that's the target. This is the standard voltage used in onroad and offroad racing for 1/10th scale electric cars. It's a consequence of them (mostly) using 2S LiPo battery packs.
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you have some variable smps who can give what you need, for sure they are not at the price of server psu's
you have some lambda 5vdc 100 amp "slightly variables / adjustables" ones on ebay ?
Nemic Lambda SR600-5/5G SR60055G SR6005 Power Supply 5V 120A
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I couldn't see any obvious reference to the minimum voltage you could set that HSTNS-PL11 power supply to. If it can go to 8.4V, that looks near ideal.
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9V with fine tune adj trimpot is probably your best bet
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Many years ago I did a bunch of testing when I was active on RCGroups. The mainstay of that was my Manson 1-15V, 60A supply. https://www.radioparts.com.au/product/33771615/sps9600g-60amp-1-15v-dc-power-supply-bench-top-dark-grey-bench-top-dark-grey (https://www.radioparts.com.au/product/33771615/sps9600g-60amp-1-15v-dc-power-supply-bench-top-dark-grey-bench-top-dark-grey) (cheaper to buy it on eBay currently from Radio Parts)
I did pay a lot less than this for it but over time it has been a great addition to my tools including serving as a bulk charger supply.
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Manson SPS9600G is a bit overkill unless you want full adjustable output.
There's no need to pay more than AUD$200 for 500W @ 8.4V
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He did mention 4S earlier on which it will do easily and can still handle up to 60A. From memory there is also a 40A option for a lot less $ in the Manson lineup but I don't have time to chase it up.
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The Manson adjustable one looks to have the current capacity, but could be a little expensive. It's given me some avenues to explore, so that's helpful.
I'll dig around on the server PSU options, the 1200W variant would seem to be designed to manage the currents required - just need to validate that it can be tuned to 8.4V.
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Perhaps the cheapest option is higher capacity LiPo cells??
Or make a high current synthetic zener (zener and active devices) and use in series with a car battery / deep-cycle SLA ? Dropping 3.6V from 12V gives 8.4V, but you'll need to dissipate 216W with 60A flowing!!
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Look at something like Mean Well SE-1000-9, 9V (7.5-10 adjust range) 900W.
That said, hacking a 12V server supply for lower output voltage is probably the cheapest way to victory, if possible, most documentation is on getting them up to 14V vehicle power, not down.
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How about just use a 3S ESC on 12V and limit the duty cycle so it performs the same as 2S?