# DC to DC converter

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#### zapped

##### New Member
Hi all.
I am new to this forum and to electronics.
Can someone help me with a with a schematic for a DC to DC converter.
I need to convert the voltage from 9Volt battery and get from 27 to 36 volts.
I have just built a circuit that requires 27 to 36 volts.
I have been using 9volt batteries wired in series.
They are just too large and costly.
All help appreciated

##### Active Member
What are the I/O current requirements? Digikey has a large selection DC-DC converters in stock. E

##### Well-Known Member
You are going to have a problem. A typical alkaline 9 volt battery (Type PP-3) generally is about a 565 mAh battery. The mAh varies a little from manufacturer to manufacturer but generally speaking about a .5 Ah battery. When you place 3 such batteries in series you now have a 27 volt .5 Ah battery. Note it is still a .5 Ah battery. So if that is what you are doing and your load runs down batteries quick a DC to DC converter won't be a saviour.

Using a DC / DC converter you would have a higher current draw than you now have just as loss in the conversion process. You don't get something for nothing. The higher output voltage comes with a cost of higher current consumption at the source plus the loss of the device lost as heat.

You have a load running on 27 to 36 volts and how much current does the load draw for a given voltage in that range?

You going to need a bigger battery or better solution than a DC / DC converter.

Just My Take
Ron

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#### MrAl

##### Well-Known Member
Hi there,

I have to agree entirely with Ron. If you use three 9v batteries in series to get 27v (good idea BTW) and you are getting 1 hour run time, then using one of the SAME 9v batteries and a DC to DC boost converter then you will only get 20 minutes run time from that single battery. That's because when you boost the voltage you loose ampere hour capacity as Ron already stated. That's life, but there are other things you can do.
For one, you can start with a 12v lead acid battery that can have many times the ampere hour (run time) capacity than a little 9v battery. With that you can boost up to 27v or whatever you need. You'll still loose some ampere hour capacity, but the loss will be a little less and besides the lead acid battery will have MUCH more capacity to begin with. For example, if you take even a 1.5 ampere hour rated 12v lead acid battery and boost it up to 27 or so volts you'll still get at least 0.5 ampere hour from it. An additional plus factor is that you can recharge the 12v battery so you can use it again.
Alternately, you can string rechargeable batteries in series, as many as you need up to something like 20. If you use 1.4v rechargeable cells that will give you 28 volts.
If you use 9v rechargeable's (not as good though) you can get away with three or four in series and then recharge as needed. The rating on these batteries isnt that good however, whereas with 2000mAh NiMH cells you can get four times the run time you are getting now with the three 9v batteries. Nice right?
If you do choose 12v lead acid (sealed gel) you have to get a charger with it so you can recharge it correctly. You also dont get as many recharge cycles as you do with NiMH cells.

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I did forget to add something. Looking at DC / DC converters. I was going to suggest a pre made unit like those made by Cosel USA. If you use the link they make a MGW151215 15 watt unit. DC Input 9 to 18 volts with a +15 - 0 - -15 output which will give 30 VDC out. Now looking to Mr. Al's post if you can use a 12 volt lead acid battery with a respectible AH rating that could work for you. Then as Mr. Al mentions, recharge the battery. The unit I mention has about a $40 USD price tag, sometimes it is easire to buy than build your own. Ron #### crutschow ##### Well-Known Member Most Helpful Member It really all depends upon how much current the op needs at 28V. #### zapped ##### New Member This circuit is drawing 2.55mA at full power. I am using a 24mm 100k 1/2 watt linear taper potentiometer as a out put control. I am going to change it to 16mm 100k 1/4 watt so that I can use a smaller encloser. I am wanting too design both circuits on the same pcb. So at this point what are your thoughts about this? #### blueroomelectronics ##### Well-Known Member Post your schematic Post your schematic #### zapped ##### New Member This is the schematic #### Attachments • 32.2 KB Views: 210 #### audioguru ##### Well-Known Member Most Helpful Member Another Colloidal Silver scam. Do-it-yourself "medicine" that is realy a poison. It turns the skin blue. I can't remember if the circuit is used to zap the patient or to make the poison. #### Attachments • 327.1 KB Views: 84 #### Reloadron ##### Well-Known Member Most Helpful Member When you say: This circuit is drawing 2.55mA at full power. That would indicate that with 3 each 9 volt batteries in series the batteries should deliver over 100 hours of operation. I'll tell you what you are going to find here with that circuit. As Audio Guru has eluded to these circuits are little more than scams. They are like snake oil in a bottle for$99.00as a cure for whatever you decide to have and if you don't have anything needing healing they give you a warm fuzzy feeling.

This forum has a collage of well educated engineers ranging in age over decades. They will all tell you the same thing. Circuits like this are a scam. There is no magic and nothing special. They attract more attention when the marketing tosses in an LED or two as people like things that blink. The circuit is little more than a low frequency square wave generator using a LM358 in what looks to be a VCO (Voltage Controlled Oscillator) configuration. As to 4 Hz. output? Somewhere around there as it is not a circuit that is a picture of stability.

As to your power questions. The existing 9 volt batteries should last at least 100 hours based on the current drain you posted. I don't know off hand of any DC / DC converters that output less than the 500 mA version I linked to earlier but I am sure there are some out there.

Ron

#### zapped

##### New Member
Okay?? To start with I have spinal injuries and a lot of mussel spasms. My mussel stem. unit quit working and I did not want to pay the BIG for another one. In my search for a circuit I ran across this one.
It works well for my needs. But I would like to change two things. 1. The size of the unit with the use of the 3 or 4 9volt batteries, and the voltage. I am using it at 27volts now. It would be better if I had 36 volts more or less.
As for the Colloidal Silver part of the circuit I just left it out as I have no need for it. This is why I was wanting a way too up the voltage from a 9volt battery.

#### blueroomelectronics

##### Well-Known Member
DIY electrotherapy is not recommended.

PS what is the model number of device that broke?

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##### Well-Known Member
All I can tell you at this point is that if the device needs to be portable the more power (voltage) you want then the larger the battery pack will need to be. Back to the beginning, you can't up a voltage wiothout paying a price in current. A DC / DC converter like I linked to will give you 30 VDC with more than adequate current, however, you will need a good sized battery of 12 volts. Like a rechargable lead acid battery.

There was a guy in these forums who actually designed and built medical units used for muscle stimulation (forget what they are called) but I haven't seen him in here for quite awhile.

Anyway, that is about it for options as to DC / DC converter.

Ron

#### audioguru

##### Well-Known Member
Very similar "Tens Units" twitch muscles by electocuting them. Most people think it is useless but a few people like it.
The guy who designed and built these "medical units" died from electrocution.

If you have a medical problem then you should see a real doctor, not a quack. Government medicare should pay for it if you are in a democratic country.

I went to a chiropractor one time. He pressed the hardest when "scanning" me then told me that it was a problem spot. He "spammed" me because of course the resistance was the lowest where he pressed the sensors the hardest. He said that \$1500 could fix me. But there was nothing wrong with me. He was a crook.

##### Well-Known Member
Very similar "Tens Units" twitch muscles by electocuting them. Most people think it is useless but a few people like it.
That's what the hell they were, we had a forum member from down under who designed those units. Following some shoulder surgeries they used them on me for muscle therapy. Not bad at all and it seemed to help in the recovery.

Ron

#### zapped

##### New Member
The circuit in the schematic acts like a cross between a tens and muscle stimulator.

#### zapped

##### New Member
I don’t like the meds. I have been dealing with this 10 years now.

#### zapped

##### New Member
Is there any body here that programs rs medical rs-4i simulators?
It has a 3v coin cell battery that if you let it run down the unit is useless.
That is what happen with mine. need a new coin cell and the software installed.
RS Medical is very proud of this service.

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