Starter box with Dewalt LiFe battery.

Trying to power my starter box with a 28v Dewalt battery, instead of tapping into the pack to get 12v for my power panel I'd like to use this high power regulator:

http://www.national....ds/LM/LM138.pdf

I can get it to put out 5A at 12 volts all day into a set of resistors, but when I connect it to my Hobbico power panel the most I get to the plug is 2A.

Why is the power panel any different?

Terry Keeley said:

Trying to power my starter box with a 28v Dewalt battery, instead of tapping into the pack to get 12v for my power panel I'd like to use this high power regulator:

http://www.national....ds/LM/LM138.pdf

I can get it to put out 5A at 12 volts all day into a set of resistors, but when I connect it to my Hobbico power panel the most I get to the plug is 2A.

Why is the power panel any different?

Click to expand...

I dont know what the hobbico panel looks like but is it possible that the panel has its own regulator rated at 2 amps ?Sounds like the panel has its own regulator that regulates at a lower amperage? (larger wattage resistors)

Just some thoughts..

Terry,

Does the Power panel output current change if you change the voltage output of the regulator?

I got one of those regs to do the same thing but never got around to wiring it all up. Does it get warm pulling 5A @ 12V into resistor loads?

Did you wire the regulator and panel in parallel? If so, over half of your current is going through the path of least resistance leaving only 2 amps to go tto the panel. To know for sure, I'd need to see how it's all wired and a schematic of the power panel

I'm pretty sure Bill is on the money.

Tim, I'd be surprised if those resistors didn't get hot.....need to dissipate the current somewhere.

Gino

Thanks much for the help guys.

The panel will put out 5A+ when I connect a 12v battery to it so it's not restricted somehow.

I have it wired in series with the regulator just as if it was connected to a 12v battery.

Increasing the voltage output of the regulator doesn't give any more current to the panel, I went to 15v with no difference, still only 2A.

Yes, it gets hot pulling 5A! At first it wouldn't maintain the current but once I kept it cool (heat sink) it'll put 5A out forever, just not to the power panel.

Tried to find a schematic but no luck, it's a Hobbico "Deluxe power panel II":

http://www3.towerhob...?&I=LXACW7&P=ML

I know it'd be easy to tap into the packs for 12v but I'd really like to leave them "stock" so I can put them on the Dewalt charger. The batteries come with their own balancer and have 8 of the A123 cells, gonna make a sweet little starter box:

Terry,

The 28V input to the regulator to drop it to 12 v and at 5A will waste crazy power! (28V-12V ) * 5A = 80W of heat, this is WAY too much for even a big heat sink really, and really more power is "wasted" in heat than used to power the panel. What you need is a switching regulator not linear one. (In affect the switching one "pulses" the power to control the voltage.)

This is close to what you need, can do 3A, not sure if they have a 5A unit, ask them!

http://www.dimensionengineering.com/DE-SWADJ3.htm

You are looking for a DC to DC converter or step down. There are some out there, web search for them.

Paul

Terry Keeley said:

Thanks much for the help guys.

The panel will put out 5A+ when I connect a 12v battery to it so it's not restricted somehow.

I have it wired in series with the regulator just as if it was connected to a 12v battery.

Increasing the voltage output of the regulator doesn't give any more current to the panel, I went to 15v with no difference, still only 2A.

Yes, it gets hot pulling 5A! At first it wouldn't maintain the current but once I kept it cool (heat sink) it'll put 5A out forever, just not to the power panel.

Tried to find a schematic but no luck, it's a Hobbico "Deluxe power panel II":

http://www3.towerhob...?&I=LXACW7&P=ML

I know it'd be easy to tap into the packs for 12v but I'd really like to leave them "stock" so I can put them on the Dewalt charger. The batteries come with their own balancer and have 8 of the A123 cells, gonna make a sweet little starter box:

Click to expand...

Not sure why you need 5 amps over the 2 but here is a pricey little item that will cover the gambit.

http://www.castlecreations.com/products/ccbec.html

(I believe this has fully adjustable amperage and voltage to 12.5v and up to 20amps.) Thats considering the source has the capability to deliver up to 20amps?

What is the amperage rating of the 28v battery that your using?

Are you getting 5 amps at the output side of the power panel (12v side)?

Or is it that you want 5amps at the plug side as well?

Thanks again for the help guys, what a resource this forum is!

Agreed, looks like a DC-DC converter is in my future, maybe something like this:

http://www.powerstre.../dc-dcz1203.htm

They also have a 5A version available. I need about 3A at the plug to get it hot enough, it can take up to about 5A to light a real cold one. I found the current going to the panel is about the same as what meter says for the plug heat.

Found a bunch of info on these packs from the electric scooter guys, they like them! Apparently they'll put out 20A (quite enough for my Dynatron) and a fully charged pack is somewhere around 29.2v. The beauty of using it "as is" is that the balancer is built in and it has a low voltage cut-out to protect the cells. The charger is also "smart" and can fully charge a pack in 1 hr. You can't just tap into them though and need a little interface board to trick the pack into thinking it's plugged into a tool, I have one coming.

Plug & play works for an electrically challenged guy like me, I routinely let the "magic smoke" out...

One thing I forgot to bring up on the "tapping in" to the battery pack, this would be a bad idea. Lets say you tap in and use 5 of the 8 cells in a pack, these tapped in cells will be drained more as they are being asked to provide more current. Now with all the need for balanced packs and now you are "un-balanced" with the load. See where this is going... the other cells in the pack would "charge" the others cells and COULD really be a bad thing. Heat, fire, smoke CAN follow next. This is why we use the balance charges in the first place. Bottom line all cells or nothing!

Do you really need to run the power panel? If it is only to drive a glow plug there are ways to do that with the as is voltage of the battery. I guess if you need the power panel for glow, fuel, and maybe some other use then this would be the path to take. The DC to DC convertors are not cheap as you now know!

Paul Traufler said:

One thing I forgot to bring up on the "tapping in" to the battery pack, this would be a bad idea. Lets say you tap in and use 5 of the 8 cells in a pack, these tapped in cells will be drained more as they are being asked to provide more current. Now with all the need for balanced packs and now you are "un-balanced" with the load. See where this is going... the other cells in the pack would "charge" the others cells and COULD really be a bad thing. Heat, fire, smoke CAN follow next. This is why we use the balance charges in the first place. Bottom line all cells or nothing!

Do you really need to run the power panel? If it is only to drive a glow plug there are ways to do that with the as is voltage of the battery. I guess if you need the power panel for glow, fuel, and maybe some other use then this would be the path to take. The DC to DC convertors are not cheap as you now know!

Click to expand...

Yup, even my "electrically challenged" brain was thinking that too.

I like this panel mainly due to the current adjustablilty and the meter, you can get the heat just right for different types of plugs and see right away if you got a dud.

Did some more digging last night, looks like one of these will work:

http://www.samlexame...ProductsID=6001

http://www.walcottcb...-volt-p-53.html

Truckers use them to power CB equipment, go figure. I see them on fleeBay for 1/4 the price.

Whacha think?

I'm not a EE expert by any means, but I do have a pretty good knowledge on this stuff. The first link looks good, I wonder what the unit cost is? Looks kind of high $, but maybe not. Looking over the specs. the temp. range is a bit low (30 deg c) so I expect at the max amps this thing MAY get up there if it is hot outside also. Not a deal breaker I'd say. If this unit is < $40 I'd say it is a winner!

The second unit has a 24VDC limit input so that may be a deal breaker for that unit.

I was looking at doing something along these lines also, went with a Makita 18V Li battery and a Finer Edge adapter for the starter (cordless) http://www.afineredgemfg.com/ and then a RCATS glow driver (it is a "pocket" unit with its own Li battery. NOT cheap mind you! http://www.rcatsystems.com/rc.php

Glad to help!

Terry Keeley said:

Paul Traufler said:

One thing I forgot to bring up on the "tapping in" to the battery pack, this would be a bad idea. Lets say you tap in and use 5 of the 8 cells in a pack, these tapped in cells will be drained more as they are being asked to provide more current. Now with all the need for balanced packs and now you are "un-balanced" with the load. See where this is going... the other cells in the pack would "charge" the others cells and COULD really be a bad thing. Heat, fire, smoke CAN follow next. This is why we use the balance charges in the first place. Bottom line all cells or nothing!

Do you really need to run the power panel? If it is only to drive a glow plug there are ways to do that with the as is voltage of the battery. I guess if you need the power panel for glow, fuel, and maybe some other use then this would be the path to take. The DC to DC convertors are not cheap as you now know!

Click to expand...

Yup, even my "electrically challenged" brain was thinking that too.

I like this panel mainly due to the current adjustablilty and the meter, you can get the heat just right for different types of plugs and see right away if you got a dud.

Did some more digging last night, looks like one of these will work:

http://www.samlexame...ProductsID=6001

http://www.walcottcb...-volt-p-53.html

Truckers use them to power CB equipment, go figure. I see them on fleeBay for 1/4 the price.

Whacha think?

Click to expand...

Thanks again, going with the Samlex unit, fits perfect under tha power panel. Not too bad, should be around $40...

Hi Terry,

EE expert reporting in.

The way the Hobbico glow plug circuit works is there is a little electornic switch that turns on and off about 1000 times/sec. This switch connects the battery to the glow plug for a very brief period of time (say 100uS) then opens and disconnects the battery from the switch for another period of time (say 900uS). Then the cycle repeats. the 100uS "on" time divided by the 1mS total time is called the duty cycle which in this case is 10%.

A typical glow plug draws ~3A when a 1.5V battery is placed across it so that means when its "lit" it looks like a 0.5 ohm resistor. (ohms law)

When the electronic switch in the glow plug circuit is "on" (closed), 12V is applied across the 0.5 ohm glow plug resistance, so 24Amps flows from the battery through the glow plug for the "on" time (100uS). Then it turns off and 0A flows for the remaining 900uS. Since the time is so short, the 24A burst does not blow the plug because the element cannot change temperature as fast as the current is changing. Instead the elemet avarages the heat generated by the current pulses so 24amps at 10% duty cycle look like teh same amount of heat generated by 2.4A average (or DC).

The knob on the panel adjusts the duty cycle to increase or decrease the current.

Now why didn't you're regulator work?

The reason that regulator didn't work is because when the glow plug circuit tries to pull 24A "sips" of current from the regulator output. Your regulator can only provide 12A "sips" before it goes into current limit. Another consideration is that the batteries must also supply these 24A "sips" of current so the battery pack voltage might be dipping momentarily while the glow plug is pulling current.

Run a test with that setup. Measure the voltage on the ouput of the regulator when the glow plug is connected. My guess is that it will drop by about 10%. If thats true, measure the battery voltage as well. It might drop as well. This could mean that the battery can't supply the instintanious current.

Whatever power supply you use to power the power panel need to be able to supply 24A peak current the whole time you're plugged onto the glow plug.

I'd call the DC-DC converter folks and ask them if their supply is OK doing this. also their return policy if it doesn't work out. I would not be suprised if the DC-DC power supply did a similar thing to the linear regulator but to a lessor degree. The dc-dc converters have capacitance on the outputs that will help with the 24A current spikes and you might squeek under the working/not working bar.

If you need anymore input just holler.

Dan_Cousin said:

Hi Terry,

EE expert reporting in.

The reason that regulator didn't work is because the glow plug circuit pulls 30A "sips" of current from the 12V battery. Your regulator can only provide 12A "sips" before it goes into current limit.

Run a test. with that setup. measure the voltage on the ouput of the regulator when the glow plug is connected. My guess is that it will drop by about 10%. This is becaue 10% of the time the regulator is in current limit and the output voltage will fall to near 0V momentarily ( ~ 100uS) then rise back to full voltage for the rest of the time say 900uS). If this is the case the regulator can supply the peak current.

Whatever supply you use to power the power panel need to be able to supply 30A peak current the whole time you're plugged onto the glow plug.

I'd call the DC-DC converter folks and ask them if the're supply is OK doing this. also their return policy if it doesn't work out. I would not be suprised if the DC-DC power supply did a similar thing. At worst, it may damage the supply.

Essentially the glow plug sircuit is shorting the supply into 0.5 ohms at for 100uS and repeating every 1mS when the glowplug is installed.

Click to expand...

Thanks for taking the time to reply Dan, yep, the voltage did drop about 10% even when I upped it to 15v.

Is there anyway to "trick" the power panel into thinking it's getting the 30A from the regulator? Maybe using a capacitor between the two?

What about modifying the panel to take the 28v directly?

I guess this is what they mean by "mosfet controlled"?

Panel probably won't like 28V directly.

Yes, MOSFET is our EE fancy name for switch. When you switch it on and off like that to regulate voltage or current it stays very cool. This is called switch mode. In linear mode (like your linear regulator) there is a significant power dissppation that you have to deal with.

I did a brief look into capacitors and the problem is the ripple current. Its about 10A RMS. Most of the caps at radio shack (readily available ) are only rated for 1A Rms max.

You could do another test that may involve magic smoke so watch your eyes.

Grab 3-4 (10 would be ideal if you could fit them) of those 1000uF caps from radio shack. http://www.radioshack.com/product/index.jsp?productId=2102507&filterName=Type&filterValue=Electrolytic+capacitors

solder them all in parallel (all + leads togther and all - leads together) and connect it to the the lead wires close to the panel. Make sure you solder the + leads to the positive (12V) lead or you'll get smoke immediately.

You'll be over the ripple current rating (hence the smoke warning) but the frequency of the current is high so sometimes you can get away with it. Put the glow plug on and leave it and check the temperture of the caps.

If you hear POP--SHHHHHH!!!!!. you'll need better caps. h34r:

You can get better caps from digikey but they will cost a little bit.

Again, thanks for your help.

Looks like I'm goin' in deep here, better point my toes...

I'll let you know how it goes.

Terry

Don't let the smoke out.

Dave Roach

make sure you wear safety glasses when you do the "pop" test. When these large caps vent they do it in one of two ways. either they POP! and release pieces in the air or they may jsut vent with a fizzle, if you inline with the vent, capacitor electrolyte may gets prayed in your face.

the Eyes are the biggest concern. Just some common sense safety tips when trying something like this.

In this case the more capacitors the better because they'll share the ripple current so get as many as you can reasonably fit on the panel.

Just remember that the linear regulator is pulling pulling 3-4 A and dropping 16V (12 - 28) so thats 64 watts. thats a LOT of heat and would take a Huge heat sink to disspate continuously. Possibly a CPU heatsink and fan from a PC could do it.

You wil have to remember to take the plug starter off the plug before say 20 seconds at a time. If you sit for minutes with the plug on the fire the regulator will probably overheat and go inth thermal protection. Those regulators usually thermal out at 320F so make sure everything around it can take that temperature.

If the Dc-DC converters you were looking at can tolerate large capacitance on the output, they would eliminate this large amount of heat. You'll have to call and ask.

Eureka! I think it's gonna work! Didn't even let any "magic smoke" out.

Got the 5A dc-dc converter, plugged it all in and was able to get a good 3A glow at the plug, held the input voltage too.

Hooked directly to the A123 cells as I found out the hard way you can't just tap into the Dewalt pack, you need an "interface" to fool it into thinking it's plugged into a tool. Got one from this guy on an electric scooter forum:

http://www.endless-s...hp?f=14&t=10986

Will post pics of the final setup when I'm done.

Thanks guys, couldn't have done it without ya!