Voltage drop down converter to 12v on Bike battery pack

[eHomer]

Pedrinho's recent thread on rewiring a battery pack got me thinking again about one of my pet ambitions.

To be able to use my 36v and 48v lithium ion bike batteries to power my 12v kayak outboard motor.

Rather than hijack his thread even further, I thought I'd better start this new one, (oops, too late )

He thought he could maybe use a drop down transformer, but was concerned about efficiency losses.

That got me thinking again, so an ebay search revealed this: http://www.ebay.co.uk/itm/DROK-Waterproof-DC-DC-Buck-Converter-48V-to-12V-25A-Step-down-Volt-Regulator-C-/331934500980?hash=item4d48d68874:g:SHkAAOSwHoFXqlcL

For just under £25, a DC Buck which sounds perfect for my needs, (and from the UK too !)

Technical Parameters:
The module is DC-DC non-isolated synchronous buck power converter.
Input voltage: DC 48V (Wide voltage range: DC 30-60V)
Output voltage: DC 12V ±0.25V
Output current: 25A (Recommend below 20A for a long term operating, working load less than 80% is conductive to heat dissipation and life of the module.)
Output power: 300W
Conversion rate: 96%
Over-current protection: 35A
Over-temperature: 150?
Dimension: 74×74×32mm



I'm very tempted to get one straight away, but I've made mistakes in the past with this sort of thing.

Does anyone have any thoughts on it ? (good or bad)

96% efficiency sounds pretty good to me, 25 amps is way powerful enough, my motor draws 15 amps max.
30-60v input voltage means I could use it with my 48v 10a and 36v 11a batteries.
Presumably the existing BMS's in the battery packs would work as now, with auto LV cut off, just seeing the Buck as a 36v or 48v motor ?

 

[Alan Quay]

Yes, if it does what it says on the tin it should work.

 

[Fordulike]

To be able to use my 36v and 48v lithium ion bike batteries to power my 12v kayak outboard motor.

96% efficiency sounds pretty good to me, 25 amps is way powerful enough, my motor draws 15 amps max.

Does the motor provide any discernible assistance? 180 watts doesn't sound like a lot.

Humour me, for I am a landlubber lol

 

[eHomer]

Does the motor provide any discernible assistance? 180 watts doesn't sound like a lot.

Humour me, for I am a landlubber lol

I'm not much of a Seadog myself, but I'm a sucker for canoes just like bikes. (can't stop buying the damn things.... )

Yes, my little Sevylor electric outboard works really well on canoes and kayaks, they slip through the water with minimal resistance compared to dinghies.

It's quoted as being 18lbs thrust (an obscure yardstick to draw any comparisons from), but it pushes me along faster than I can paddle.

It's sold under many "badge" names, and gets good reviews and feedback on kayak forums. It's very light, only 3.6 kgs, which is why the weight of most lead-acid leisure batteries spoil the combination, weighing around 17kg for 65 a/h.

View attachment 15448 View attachment 15448

 

[Deleted member 4366]

I've got a load of those Hobbyking 5Ah 4S lipo hardpacks. I use a balance board so that they can all be connected in parallel for charging, and I modified the board by strengthening the tracks on the back so that it can be used for discharge via the upgraded power leads.

I have a separate harness that connects the packs into a 12S1P OR 12S2P for powering an electric bike.

Running a 12v outboard motor at 4S gives it a lot more power, just like running a 36v bike at 12S.

http://www.hobbyking.co.uk/hobbyking/store/__18631__Turnigy_5000mAh_4S1P_14_8v_20C_Hardcase_Pack_US_Warehouse_.html

http://www.ebay.co.uk/itm/LiPo-Charging-Adaptor-Board-2-6S-Charge-Balance-Board-for-imax-B6-B6AC-/252323991277?hash=item3abfae8eed:g:Qq8AAOSwoudW63qZ

 

[anotherkiwi]

4S lipo would be my choice, the motor should be able to handle 15 V.

Damn d8veh beat me to it!

 

[KirstinS]

4S lipo would be my choice, the motor should be able to handle 15 V.

Damn d8veh beat me to it!

Only to add the 4s multi star (5200mah) are half price at 15quid right now

I bought two on friday

 

[eHomer]

If the 25amp Buck voltage dropper is indeed 96% efficient, then it will be more convenient for me to use it with my two 36v 11ah lithium ion cycle batteries than my DIY Lipo battery with the six 4s 5000mah packs.

I have to use that carefully with an audible lipo alarm to know when the voltage drops to 3.6, whereas the lithium ion packs are more idiot proof, (for when the family uses the setup), because they auto-cutoff with the built in BMS boards.

Recharging is more idiot proof too, with the much simpler bike battery charger that they came with, rather than setting up my universal Lipo charger.

I'm hoping each of my 36v 11a/h batteries will give me 12v at about 30a/h, allowing for the conversion losses.

That'll give me the same working capacity as my 65 amp 12v lead acid leisure battery, at about a third of the weight, and with a much longer usable charge cycle life.

It gives me maximum versatility as well, as my two bike batteries are used in three of my pedelecs, like here, in the Hase.

 

[Deleted member 4366]

Is 20A enough? That sounds a bit low for an outboard. IIRC, mine's 40A.

 

[eHomer]

Is 20A enough? That sounds a bit low for an outboard. IIRC, mine's 40A.

Yes, the majority of electric outboards, like Minn Kotas do pull around 40 amps, like you say.

The one I use on the kayak though is an 18lb thrust model, sold under the name of Sevylor, Watersnake, Bison etc..

They're just under half the weight (about 3.5kg) of the smallest Minn Kota (about 9kg) , but give plenty of thrust for a kayak.

Mine draws about 15 amps max.

 

[Deleted member 4366]

That converter should be OK then. Let us know how you get on with it.

 

[eHomer]

Ok, now ordered !

I'll certainly give feed back on how it performs, current drawn, duration etc..

In fact, I've also just splashed out on the newer T24 outboard salt water model. Same physical size, but with 24 lbs thrust instead of 18, and components that can withstand seawater rather than just fresh.

The max current consumption is still under 20 amps, apparently.

Here's a youtube vid where a chap added a DC variable speed controller to slow down his 18lb thrust motor. He mentions the current draw at each speed.

 

[IR772]

Well if you too would like to trawl for trout.

You could connect your 36 volt battery directly to this if you feel competent, just make sure you turn the speed to minimum and start the motor in speed 1.

With a bit of playing you should be able to use from min assistance up to about 50% with no detriment at all.

The motor does not look that demanding so the controller will operate in speed 1 or 2 quite happily.

If you are not so confident reduce the voltage to 12 volts then use the controller.

http://www.ebay.co.uk/itm/Motor-Speed-Control-2000W-10-50V-40A-MAX-DC-PWM-HHO-RC-Controller-12V-24V-48V-UK-/161975055276?hash=item25b67733ac:g:sGYAAOSwDuJWvFZ2

 

[eHomer]

I'd seen that variable voltage controller already, but I have to admit that it never occurred to me that I could use that on its own to get the 12v out of the 36v.

I guess I could fit a physical stop to the potentiometer to give it an upper limit of about 15 volts.

Two thoughts come to mind though, is the voltage conversion on that as efficient as the buck converter ?

...and if it failed, could it surge the output voltage and damage my motor ?

A very good pice though, and 40 amps capacity gives a nice safety margin.

 

[IR772]

If its you using it, a bit of tippex on the dial will do as a marker.

PWM is the industry standard way to get high power DC control

Usually these things fail open circuit rather than "on", so if the magic smoke comes out every thing will be safe and you will need to spend another £7.

I think this would be the most efficient control mechanism, you will have some switching loss but at this level that is not a problem.

As far as the rating your 10 or 15 amps at 12 volts will be good with this unit, I would not take it to 40 amps and want to be in the same room.

Once you get it working put it in a sandwich box or similar as getting water in it will then require the paddle.

 

[eHomer]

I can't resist it any more, you've convinced me I need to try it...

I'll test it as an alternative to the Buck, amps drawn etc..

I'll still feel safer with a physical stop on the controlling pot though (family might be using it) , I don't want to burn out my outboard, it cost £90....

I like the additional bonus of being able to run it up to about 14 volts , like a fully charged SLA, or even maybe 16v like d8veh's 4s lipos.

Is 40 amp output the highest that these very reasonable cost PWM's go, before getting too expensive ?

I was thinking if they do a cheapish 60 or 80 amp, then I could use it with my larger Minn Kota as well, as d8veh said, they run at about 40 amps max.

 

[eHomer]

I've found a 60 amp PWM on ebay, at £20.59, (from Jersey, UK)

http://www.ebay.co.uk/itm/60A-DC-Brushed-Motor-Speed-Control-PWM-HHO-RC-Controller-12V-24V-48V-3000W-TE573-/331951750406?hash=item4d49ddbd06:g:tSsAAOSwV0RXwIZ7

It would need mounting in a container though, unlike the self-contained 40 amp version.

I've just realised a flaw in my logic with these things.

I suppose it won't show a gradually increasing DC voltage as it's turned up, because I believe it's pulsing the full input voltage, to reduce power output ?

If so, I guess I'd need to measure the motor rpm (with my optical rev counter) to find the "12 volt" setting ?

 

[eHomer]

I just thought of googling this, and there's some very interesting hits for pwm's with trolling motors:

https://www.glen-l.com/phpBB2/viewtopic.php?t=7680

It looks as though the PWM is more efficient anyway....

 

[IR772]

If you have a multi meter then the set up of the max voltage/speed is easy, you then tippex and set up your physical stop to be less than or equal too that point.

I would try the second motor with this controller as well. If you use your meter you can watch the current when you have a play.

If you gently increase the level up to about 15 amps then switch over and see what voltage that is, progress until you get to 12 volts you may be surprised that the maximum current is no where near rated MAX.

For short use in testing I can not see it causing a problem as all the current ratings are MAX so there is plenty of room to build up to.

Have a play with this unit to see if it works for you then you can look at powering the QE 2.

 

[eHomer]

Thanks IR, I'll wait for the toys to arrive, then give feedback on here and send technical advise to Cunard.