LM5007MM DC-DC 80 volts step-down converter

Hello everyone.

This is my first post but I've been lurking since I completed my first E-bike project about 8 months ago. I'm a total noob with bicycles, electric bikes and all things electrical so I'm grateful for the amount of knowledge that you all have been sharing. I have a Giant Revive with a Crystalyte Journey Kit and I love this bike! My son and I have come to depend on it everyday. It has a 408 at the front switchable to the extra motor (a 4011) at the rear, and a 36v 9ah NiMH pack (shows up 42.5 volts on the multimeter). This pack has lost some distance range a few months ago, possibly due to overcharging/topping-off. I started to research other battery options and found members of Endless Sphere and V is for Voltage using Dewalt packs. I bought one Dewalt pack and a charger and found that 33v is sadly lacking, and my controller cuts off at maybe 29.5v. I bought a second Dewalt pack which I will experiment with in series. My controller is for 36 volts (and maybe up to 48 volts?) So I figured the two Dewalt packs in series at 66 volts will need to be stepped down. I googled around and found the LM5007 80v DC-DC step-down Buck converter.

http://www.national.com/pf/LM/LM5007.html

Again, I am electrically challenged compared to you guys. Am I on the right track here? Is the LM5007MM what I need? Or should I just buy another controller? Thanks in advance.

J

A single Dewalt pack is only 2.2ah, you might find better performance if you have 2 or 3 in parallel. (Less voltage sag).

There are a few threads on DC/DC converters. Here's a good one
http://endless-sphere.com/forums/viewtopic.php?t=2264

Hi Ted, thanks for the tip!

I've heard of "Volt sag" or "Voltage Drop" but didn't worry about it until now. I wasn't sure what it was until after I hooked up my multimeter for test rides only recently. My analog multimeter is old and bulky and I didn't want to mickymouse it with duct tape or wire straps as I'm trying to keep the frump on the down-low. I finally found a small and cheap handheld digital multimeter which I temporarily strapped until I find a small analog panel voltmeter to hardwire. Now I can see how the volt drops down and bounces up while riding. Good to know...

I'm glad you reminded me to try parallel first. Yes, I meant to go parallel first with 2 packs to experience how amp hours affect motor performance, but was also preparing to try series if parallel didn't cut it.

I was under the impression that VOLTS provide strength and speed, and AMP HOURS gives distance. So doubling to 4.4 ah will increase the "performance" (as in strength and speed)?

I read about how Russ Finley aka "biodiversivist" was using one pack at a time before he went with 2 in series so thought I one pack would be enough for my short rides.

http://gristmill.grist.org/story/2006/9/8/82015/17778

This past summer my NiMH pack got me between 24 and 27 kmph on a fresh charge on my 408 on 20" rim, but weakened down to 22 to 23 kmph after several km. With one Dewalt pack BMS bypassed, the current draw was about the same as my NiMH pack and the power consistent as advertised, but I was limited to a sorry 20 kmph. Now I can't imagine how BioD got by with just one pack.

I'll eventually go series to raise the volts just a bit more but don't want to buy a new controller, so the my questions still stands. Can I use the LM5007 to step down to 48 volts? Can I draw enough amps through it?

J

Hi Deejay,

The specifications on your DC-DC convertor says that it can only provide 500 mA, which is only a half an amp. It would not be able to drive your motor.

The reason that more parallel batteries and Amp Hours translates to better performance with these batteries, is that putting them in parallel reduces the voltage sag.

For example, if you have 2 volt of voltage sag with 1 battery because you're drawing 20 amps through an internal resistance of .1 ohms, you will only have 1 volt of sag with 2 batteries in parallel. Less sag, greater voltage, higher speed.

I'd go with a controller that can handle higher voltage and more amps.

I hope that helps.

Brian

Yes, a dc-dc converter is not the way to go.

With more packs in parallel, you should find you don't hit the low voltage cutout until the packs are really dead.

Depending on what model of controller you have, it might be able to take 72v. Make sure before you try.

Hi Brian. Thanks for taking the time to breaking it down in that example for me, it made a lot of sense.

fetcher, my controller has Low Voltage Cut-Out as well as High Voltage Cut-Out. But you're right, I should confirm it anyway. As I said earlier, my son and I depend on this bike everyday so I can't afford to screw it up. It's about time I invest on a back up controller and throttle.

The NiMH pack lost some range but still has much life in it, I just need to keep it topped up but not overcharged. Good thing I'll have the Dewalts for extended range.

Also, by the time that hefty thing is on its last leg, I will have installed a two speed hub kit on my wife's Revive running on the two Dewalt packs and then I'll really get going with four Dewalt packs.

I am so excited to try out two packs, or maybe even three. The second pack should arrive in a few weeks.

A GODZILLION THANKS TO YOU GUYS! AND AND A HAPPY HOLIDAYS IN ADVANCE!

Hold up... did I just hit the jackpot?

What if I parallel two of these bad boys? SV48-24-200-1

Input 36-75Vdc
Output 24Vdc 10A

http://www.roassoc.com/products/superv.htm

You might get about 80% efficiency.

:?

Thanks for pointing me to the efficiency,TD.

Disappointing but I'm still glad to learn that it's possible to parallel these Buck converters for future reference.

My second "Dewalt Paquette de baterias de 36 voltios de alto redimiento" arrived just now! :wink:

Interesting to know that Hispanics are such large consumers of E-bike batteries *chuckle*

Time to go parallel... tra ~ la ~ la~ ~ ~ 8)

At least it's not DeWallt, or DeValt.

If you are looking for a fine watch, I will gladly sell you my Rolmex.


8)

There's some speculation that the drill motor controller built into a DeWalt pack can be used as a buck converter. Somewhere around here there's a diagram showing how to hook up a potentiometer to the pack to control the "drill speed".

By adding a diode and inductor, you could feed the input to a controller at reduced voltage. With two batteries in series, only one would need to have the control installed, since only one switch is needed. The combined series output from two packs would go into a single inductor/diode setup.

The output would not be regulated, so might vary with load quite a bit.

At 50% "drill speed", the output should be about half of the combined battery voltage.

Rolmex... ~lolz~ TD, here's a Mexican joke for ya in my best mexican accent:

Senor, du ju no wat alak en de wemens? Me d!ck... :wink:

Anyway, I got two packs now and in the parallel. The packs are saying "Up up and away!", but the controller is saying, "No way, Jose"... or maybe the Dewalt BMS is regulating or the controller is specifically designed for NiMH only. I'm stuck at 20 kph... Does anyone here know how and why some controllers are designed for NiMH only?

Oddly, on my ammeter, under dead-stop load, I surge over 20 amps! Even odder, I haven't blown the 20A fuse. I thought amp draw depends on your controller, motor, and throttle, not the battery or it's configuration?

fechter, thanks for that, I'll definitely look into it if I solve this 20 kph limit. Otherwise, I'll just order a 36v - 72v 40a controller. I just hope I can get the same slim case like the Journey kit...

By the way, I'm loving these APP connectors, they're like Legos. I can reconfigure my packs into series or back to parallel. But they're not DeeJay-proof, I actually made the mistake of plugging my NiMH to the Dewalt pack! YIKES! Lucky for me my NiMH pack's switch was on "off". I nearly shat...

Please have a look at my bike

http://endless-sphere.com/forums/viewtopic.php?p=41455&sid=f3de60c19f015c0b0477e7ff8de169e5#41455

No offense intended with my minority jokes, after all I'm a minority of minorities...

Nice ride! Giant's version of scooterbike...(?)

The DW bms can be bypassed. Search the board, cuz I don't recall which blades are direct / fused / etc.