Really high-current voltage regulators

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1

When using batteries with high voltage swings, like LiPo or LiFePO4, the swing in voltage from high to low can cause trouble. Either you exceed rated voltages at the high end, or you get no torque at the low end. This is a problem even with NiMH batteries to some extent, and certainly a problem with LiPo and LiFePO4.

Pololu has some nice switching voltage regulators – especially the new buck/boost controller with over 90% efficiency is very nice! But too low current to be useful for power hungry servos and motors.

Digi-key has some nice parts, too – I like the GE/Lineage raptor, for example, for generating 6V at 10A from a 3S LiPo: digikey.com/scripts/DkSearch … =0&cur=USD (this needs a few additional capacitors and some hookup to make a finished product.)

Building these kinds of things yourself is hard, because none of the low-volume “prototype” board houses do more than 1 oz copper plating on their boards, and high-power boards need 2 or even 3 oz thickness for traces.

Wouldn’t it be great if Pololu had hobby robotics regulators designed to take, say anything from 2S to 4S LiPo, and output something like 12V / 25A? Or, if buck/boost for this amount of current is too hard to solve, a buck-only converter that takes 4S LiPo in and outputs an even 12V / 25A would be good, too.
You can buy things like this, but they are built on heavy steel frames, and cost many hundreds if not thousands of dollars, and are based on older designs. With modern chips and parallel MOSFET switchers, I bet these could be built to sell for, say, $50 each as bare boards.

Another hole in the availability spectrum is battery cell controllers. Places like all-battery sell LiPo and LiFePO4 cells, as well as the necessary battery management circuitry to turn those cells into “safe” battery packs, with overcharge and underdischarge protection. However, those boards typically top out at 10A to 15A. A hungry robot may want to draw 50A or more. A battery protection/management board for hobby robotics with those kinds of amperage ratings would be sweet! Again, you can buy BMS-es that do this, intended for scooters or cars, that are way too heavy and way too expensive for hobby robots.

2

Hello.

Thanks for the suggestions. Making some higher-power regulator products (though maybe not quite as high current as you’re asking for) has been on our to-do list for a while, and I’m constantly looking for new regulator products, especially in the buck-boost realm. Unfortunately, Linear is still the only place I know of that has a controller that can approach the kind of performance we would like, and their stuff is very expensive. The part, LTC3780, has also been out for a while, so I keep expecting some lower-cost alternatives to appear from some other manufacturers. But, I get uncomfortable once the price gets past about $25 for a voltage regulator product, so it’s good to have at least one data point of someone open to a $50 regulator.

- Jan

3

I think Maxim and Micrel has some useful parts, too. In general, there are switching regulator controllers that let you pick your own external MOSFET, and even include totem pole boost capacitors for driving high-side N-channel MOSFETs for you. With high-current fast-recovery diodes, high-current switching MOSFETS (two, maybe) and high-current inductors and MLCCs, you are probably looking at retail price of more than $25, though.
Also, most of the parts these days are either aimed at ATX power supplies, where things like multi-tap flybacks make sense, or at cell phones, which is a different kind of beast entirely.

FWIW, the main challenges I’m running into in trying to do this myself are:

  1. All the nice parts are SMD only. I haven’t yet dared take the leap to toaster oven soldering.
  2. Board layout is actually very important. I can’t make my own “real” boards (breadboard FTW! :slight_smile: and the iteration cycle of sending to China or OSH Park for each new board is expensive and slow.
  3. You really need 3 oz copper for the really high-current stuff, and no home boards (breadboard, blanks for etching, or even sub-$100 board houses) do more than 1 oz.

If you are going high-current, I seriously suggest going for 50A or so! 10-15A can be had off the shelf, at least in certain voltages. There’s even a hobby/RC 20A regulator with adjustable output for $49 here: store.rcsupersales.net/servlet/- … tor/Detail
If you could do 50A for the same price, well, you’d have them beat :slight_smile:

4

50A seems tough. Is using multiple lower-current units an option for you?

- Jan

5

Worst case, yes :slight_smile:

The main need for these is when using servos with upper voltage limits. 7.4V or 6.0V hobby servos, 12.0V or 14.8V robot servos, that kind of thing. Especially the Robotis servos have an overvoltage lock-out at 16 Volts, and are specified for 12 or 14.8 Volts, and a fully charged LiPo will overvolt the servo and trigger the overvoltage alarm (and presumably endanger the servo.)

While it would be convenient to have one of these guys for all servos, one per “string” of servos would work, too. I’m also playing with the idea of partially pre-discharging the battery to get under the upper lockout voltage…

I found this:
digikey.com/scripts/DkSearch … =0&cur=USD
40 Amps for $30! And not in a shoddy Chinese hobby catalog like “Hobby Pope” or whatever, so it might actually meet rated current.

It’s almost what I want for hobby servos, if it could get up to 6.0V. And a 12 (or 14) Volt version would be sweet for Robotis servos.
You might want to get one and run it through its paces to get inspiration :wink:

6

Looks like the input maxes out at 13.8 V, but it does look like the module might be worth looking at. But I think for things like servos in particular, it’s usually nice to break it up into several power rails, anyway, to prevent having to wire things with really thick wires.

- Jan