Building a battery controller

[Welshbloke]

A while ago I built a cheap but effective (ish) PWM controller using a motor control PCB from ebay, a DPDT switch, a project box and the sockets needed to accept a 12v DC input and a Kato track power supply socket output. I say ish as some motors won't actually stop with the knob turned right down!

 

Since then I've acquired another PWM module for less than a couple of pounds on ebay and read up on 18650 batteries. Which led to this test rig:

 

The green power bank and USB lead will be replaced when the next part of the puzzle arrives. I've ordered an empty power bank casing which is designed to hold and charge up to five 18650 cells in parallel, by only fitting three or maybe four I should free enough space to fit this extra circuit, which I'll patch onto the USB output pins of the power bank circuit board. So far it draws one or two milliamps when powering a Bandai DD51 hauling four coaches, so even if I can only fit three batteries that should give an impressive runtime. It'll also double as a power bank, just one with an extra switch, knob and socket at the opposite end to the USB connections.

 

As for the train refusing to stop, this one has a positive "off" setting with a click! The train starts moving at about halfway around the dial so the click has no impact on fine control.

 

[gavino200]

That looks amazing. I'm not sure I understand the concept though. Is this so you can make a small portable layout that doesn't need to be plugged in?

[cteno4]

Very cool! I have a couple of those inexpensive pwm boards and have been meaning to see how they do with trains. Sowanted some cheap and replaceable systems for kids controllers when we set up those loops.

 

2ma sounds really small draw for a motor like that.

 

jeff

[Welshbloke]

Yep, I was inspired by the Tomytec battery controllers from about a decade ago. Tomix have shown no signs of re-releasing them so I decided to have a go. The wiring is very simple thanks to using the proprietary PWM control board, about which I know little beyond its input range. The DPDT switch is wired to switch polarity and reverse the train, with the input feed to the centre pins and the output from the outer pins at one end. Two crossed wires between the four outer pins give reversed polarity when the switch is flicked, and a centre off position like the Kato mains controller.

 

Not entirely sure how much use it'll get, this is one of those projects where the construction is interesting enough to justify the effort. But one of these and a compact track pack (like Kato CV1) and you could run Shorties or (probably) Tomytecs anywhere. It might even handle some fully fledged Kato stock, the RhB range doesn't seem to draw much current and will move on low voltages.

 

It wouldn't be difficult to hard wire it into a micro layout either, you can buy lithium cells, holders and charge circuits easily. I'm using the power bank casing as that provides the charging circuit and a project box in one, it'll cost a little bit more for the cells but this way I know I'll get good ones which offer somewhere near their claimed capacity.

 

I thought 2mA sounded low so rechecked. It's actually 20-30mA at full speed. Misread the display showing 0.02A. Normal speed running is about 10mA.

[The Next Station Is...]

Love the idea - I might follow your lead! (terrible pun totally intended) 

[Welshbloke]

The only difficult part is the Kato socket to plug the feeder track into. On this one I used the socket from a turnout extension cable (the plug and most of the wire of which was soldered to another turnout lead I received minus plug with a used turnout). Previously I used one of the adapter cables Kato sell for using other controllers with their track.

 

One snag is that I can't really post eBay links for items as they'll be outdated fairly quickly. I can offer a list of search terms though:

 

"PWM Controller" and search lowest price first. You want one which can run from 5v DC or less. Most seem to be able to handle well over 12v so you can build a mains powered one using a commercial transformer, my previous one (in a dedicated project box) uses a 12v DC output wall wart from an old Netgear router.

 

DPDT switches are easy to find. I used an On-On type last time, this one has a centre off position. I like clicky toggle switches but you can buy sliders if you prefer.

 

The power bank part is down to personal preference. I searched for "power bank 5x 18650" and ordered one of this type: https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F263812727431

My plan is to leave the bottom one or two battery slots empty, cut the terminal rails back, and use that space for the control circuits. There should be enough room to run a couple of slim power wires up to the USB charging board at the top end. The speed and direction controls should hopefully poke through at the bottom edge with the output socket at the side.

 

You can buy bare 18650 charger boards and battery holders if you want to build it into something oddball. One word of warning though, lithium batteries react badly to being shorted out. Very badly! If your chosen casing is metal then make sure everything is insulated and nothing can short against it. I'm using the power bank shell as it's designed to hold and charge the batteries safely, so my additions shouldn't pose a hazard. They're also not fond of being assembled into a battery where the individual cells have widely differing charge levels, so keep them as a dedicated pack for this rather than sharing them with other devices.

 

Do some research into 18650s too, there's a big problem with fakes. I plan to buy more from an apparently reputable seller I bought a couple from last month, as the casing isn't designed to be reopened and I need the ones I already have for my torch. I shall use one of them to test it though, before spending more than all the other components put together on batteries.

 

If you don't fancy fiddling with lithium cells you can just as easily build it into a project box with a USB power socket, micro USB sockets on small header boards are easy enough to come by. Then plug it into a mass produced power bank or a mains transformer.

 

Look up a YouTube channel named "Big Clive" for more on the power side of this, I learned a lot from watching him pull various devices apart.

[Welshbloke]

The other parts arrived, so here's the finished build:

 

 

 

These casings take flat top 18650s rather than button top, luckily the buttons popped off mine to reveal a flat top. I ran a couple of wires under the battery holders and soldered them to one of the USB outputs for power, the rest of the wiring is visible. Currently waiting for the glue holding the output socket to harden fully before I clip the lid on.

[cteno4]

Very nice work!

 

jeff

[Welshbloke]

Thanks, modifying the case was easier than I expected. I also found another use for leftover foam from Casco cases - a chunk is now wedged behind the output socket as the glue didn't seem all that reliable.

[ianlaw]

Maybe too late but maybe this can help someone else....

You can use a Rokuhan controller, which can be powered by an external transformer or by adding batteries in the battery compartment. Intended for Z-gauge. I have used one for the last few years for both my BR and JR layouts. Look on this page: http://www.rokuhan.com/english/products/controller/ for RC-02.

[Welshbloke]

I have an interesting problem after testing it properly. It doesn't draw enough current to keep the power bank circuits awake!

 

The Poundland power bank I used for initial testing keeps its output pins live until the battery voltage drops too low. This one cuts off if it can't detect a load. Given the control circuits only draw 10mA or so this evidently isn't enough! It might be better with a full size N train instead of the Bandai chassis, or pairs of Shorties.

 

I will try it again with the built in LED torch switched on and see if that helps, silly though it will look.

[Sheffie]

You might be able to use a different rating of potentiometer for your potential divider (assuming that’s how your throttle control works). A lower resistance should give you enough current draw. 

[Welshbloke]

It's a bit awkward in that it's a PWM circuit, and I'm not sure how they work. I have found that if I plug a USB torch into one of the ports it remains live, need to try double heading trains and also see how it gets on with full size N (as opposed to shorties).

[The Next Station Is...]

23 hours ago, ianlaw said:

Maybe too late but maybe this can help someone else....

You can use a Rokuhan controller, which can be powered by an external transformer or by adding batteries in the battery compartment. Intended for Z-gauge. I have used one for the last few years for both my BR and JR layouts. Look on this page: http://www.rokuhan.com/english/products/controller/ for RC-02.

 

Here's an idea - I came across a 5V USB to 12V 5.5mm jack step-up adapter cable on eBay. This could work to hook up a USB power bank to a standard controller, as long as the current draw isn't too high. As I've got one of these Rokuhan controllers, I'm tempted to give it a try (as an alternative to using AA batteries). It wouldn't be as convenient as an all in one solution, but seems easy to try! 

[Welshbloke]

Double heading and running at a reasonable speed kept the circuits awake, as did plugging a USB torch into one of the output ports on the power bank circuit. The latter was more useful for control in that you can still run slowly, but leaves you with a bright light and a surprisingly warm aluminium object (the casing is a heatsink for the COB LED).

 

I have ordered some more components, so I'll probably build one which takes a feed from a standard power bank via a micro USB port next. Want to find an unusual casing for it, inspired by the headphone amps I saw ages ago built into an empty Altoids mints tin. Or alternatively a mini module with it hidden inside a building or something...

 

Comes to something when you can assemble a perfectly usable controller for under £10, including a power bank to feed it from! If you're in the UK grab one of the £2 or £5 ones from Poundland as they don't shut down in response to low current draw, only when the battery voltage drops will they cut off.

[The Next Station Is...]

I've been testing using a voltage step-up converter (embedded in a cable), which takes a 5V USB input and outputs 9V via a 2.1mm barrel jack. This works fine with a Rokuhan RC-02 controller; I also bought a PWM motor controller from eBay but had the auto switch-off issue with that. I think the Rokuhan controller's constant lighting feature creates a permanent current draw and thus the power bank doesn't turn off.