Rigol DS1000 series, battery power ideas.

[Lightages]

I have been enjoying the use of my hacked DS1052E but have been wondering about how to make it more portable and make it an isolated scope. After looking at the schematic made by A Hellene, I started to think it might be possible. But he PSU schematic has a line frequency derived 50/60Hz source supplied to the main board. Any ideas what this might be for?

EDIT: Aha, I see from A Hellene's schematics that this mains frequency signal is fed to the trigger circuit. It is probably a simple way of providing a free run trigger signal. So it probably can be replaced with a simple oscillator to do the same thing.

Beyond this unknown item, there are basically 3 voltages needed to be supplied; -12VDC, +15VDC, and +6.4VDC. The scope also uses has a +3.4VDC supply, but this is derived from the +6.4VDC.

The simple thing to do would be to make an 18VDC battery pack and regulate it down to +15VDC, and then have another regulator to supply the +6.4VDC. Then add a small DC to DC inverter to make the -12VDC. Many parts, much to be concerned about, and a need to switch the battery pack into the existing circuit.

A more simple, but brute force, thing to do is just install a 100VDC battery pack and have it supply the input side of the whole switching power supply. This seem rather inelegant, and dangerous too. I don't like the idea of such a high voltage battery sitting there ready to make a mess of things.

A Hellene's post with his PSU schematic can be found here.
https://www.eevblog.com/forum/index.php?topic=3738.0

Any thoughts?

[mikeselectricstuff]

I have been enjoying the use of my hacked DS1052E but have been wondering about how to make it more portable and make it an isolated scope. After looking at the schematic made by A Hellene, I started to think it might be possible. But he PSU schematic has a line frequency derived 50/60Hz source supplied to the main board. Any ideas what this might be for?

Line trigger mode - obviously not needed when on battery

[Lightages]

LOL, I edited just as you posted....

[A Hellene]

I had thrown an idea about that, using a couple of SiC413 (of >90% efficiency) for the generation of the 6V40/1A4 and the 3V35/1A3 power supplies and an AVR microcontroller for the generation of the -8V0/-0A5 and the 15V0/50mA ones plus the supervision of the input/output power and the battery state.

But any further research for and the development of this very high efficiency, battery powered PSU were postponed due to the malfunctioning DS1052E I received...


-George

[ejeffrey]

EDIT: Aha, I see from A Hellene's schematics that this mains frequency signal is fed to the trigger circuit. It is probably a simple way of providing a free run trigger signal. So it probably can be replaced with a simple oscillator to do the same thing.

It is used for measuring signals that are synchronous or nearly so with the AC line voltage.  For instance, imagine you are measuring a linear PSU with a couple of mV of ripple at 2x line frequency.  The signal itself is not big enough to reliably trigger.  Turn on line triggering and you will easily see the ripple waveform.  Another example is if you are measuring vibrations caused by induction motors.  They rotate at a fraction of a Hz less than the line voltage (or half that).  An oscilloscope on line trigger mode will show a nice 'walking' waveform which can allow you to quickly distinguish 50/60 Hz electrical noise from a mechanical vibration caused by an AC motor.

[Lightages]

It is used for measuring signals that are synchronous or nearly so with the AC line voltage.  For instance, imagine you are measuring a linear PSU with a couple of mV of ripple at 2x line frequency.  The signal itself is not big enough to reliably trigger.  Turn on line triggering and you will easily see the ripple waveform.  Another example is if you are measuring vibrations caused by induction motors.  They rotate at a fraction of a Hz less than the line voltage (or half that).  An oscilloscope on line trigger mode will show a nice 'walking' waveform which can allow you to quickly distinguish 50/60 Hz electrical noise from a mechanical vibration caused by an AC motor.

Yes of course, I should have remembered that! This is not my first oscilloscope but I have nit used line sync for such a long time.... We can just forget that part of the circuit for battery use.

[Lightages]

I had thrown an idea about that, using a couple of SiC413 (of >90% efficiency) for the generation of the 6V40/1A4 and the 3V35/1A3 power supplies and an AVR microcontroller for the generation of the -8V0/-0A5 and the 15V0/50mA ones plus the supervision of the input/output power and the battery state.

I thought I remembered seeing someone mention a battery idea before. So if we are going to build a complete power supply, why not replace the power supply in the scope altogether? I can see that with a battery we would not want LM317s in the circuit wasting all that power.

I was hoping there was a simpler answer. complete rebuild of the power supply will not be a cheap hack.

[Zero999]

I have been enjoying the use of my hacked DS1052E but have been wondering about how to make it more portable and make it an isolated scope.

If you just need isoilation, use a transformer.

After looking at the schematic made by A Hellene, I started to think it might be possible. But he PSU schematic has a line frequency derived 50/60Hz source supplied to the main board. Any ideas what this might be for?

EDIT: Aha, I see from A Hellene's schematics that this mains frequency signal is fed to the trigger circuit. It is probably a simple way of providing a free run trigger signal. So it probably can be replaced with a simple oscillator to do the same thing.

What about using an antenna and filter tuned to 50/60Hz to generate a signal with the nearest mains power point?

A more simple, but brute force, thing to do is just install a 100VDC battery pack and have it supply the input side of the whole switching power supply. This seem rather inelegant, and dangerous too. I don't like the idea of such a high voltage battery sitting there ready to make a mess of things.

That's not as dangerous as you may think. The voltage is completely isolated from earth and if you disconnect the battery from the 'scope then you can easily make the 100V battery only 50V by disconnecting it in the middle.

You may need more than 100V though to get decent battery life, it depends on the minimum operating voltage of the DC-DC converter.

[Lightages]

That's not as dangerous as you may think. The voltage is completely isolated from earth and if you disconnect the battery from the 'scope then you can easily make the 100V battery only 50V by disconnecting it in the middle.

You may need more than 100V though to get decent battery life, it depends on the minimum operating voltage of the DC-DC converter.

100V of batteries is not a desirable thing though. 50V and higher is inherently a dangerous thing and to be avoided especially if we have less experienced hobbyists read this and want to try it. The other thing is that the linear regulators used after the switching power supply are rather inefficient for battery use.

I think now that it has become clearer to me what is going to be needed, I will start working on a complete replacement for the PS in the DS1052E and make it so that it will also accept battery input and be efficient. But this is only worthwhile IMHO if it can be done for under $50 or so.

[alm]

Make sure you only use it for SELV (<60VDC or so, separated from mains, ACV limit is even lower) while on battery. The scope is designed under the assumption that ground is always at a safe potential, you should not violate this assumption. No attempt was made to isolate the user from ground. Ground is also expected to be relatively low impedance for EMI purposes. Most manufacturers recommend to ground the scope while it's operating from battery, especially when dealing with dangerous voltages.

If you want an isolated scope for dangerous voltages, get something like the Tektronix TPS2xxx series or Fluke ScopeMeters, which have a fully isolated front-end.

[jahonen]

Make sure you only use it for SELV (<60VDC or so, separated from mains, ACV limit is even lower) while on battery. The scope is designed under the assumption that ground is always at a safe potential, you should not violate this assumption. No attempt was made to isolate the user from ground. Ground is also expected to be relatively low impedance for EMI purposes. Most manufacturers recommend to ground the scope while it's operating from battery, especially when dealing with dangerous voltages.

If you want an isolated scope for dangerous voltages, get something like the Tektronix TPS2xxx series or Fluke ScopeMeters, which have a fully isolated front-end.

While the safety issues are very true, safety grounding usually does not improve EMI/EMC properties. It has way too high impedance for that purpose. While the Y-caps are connected to the chassis does not mean that they should be optimally connected to safety ground, but there are usually no other options. Y-caps just close the RF current loop before it leaves the chassis. Cutting the ground will usually improve radiated emissions, but of course that can't be done due to safety issues. Sometimes a ferrite is used in safety ground to raise its impedance to reduce emissions.

I don't thing that making any arbitrary scope "isolated" by just making isolated power supply (by any means) a good idea, because if scope is connected to hazardous circuit, then all exposed connections (like other input channels and USB connectors etc.) will become hazardous in respect of the environment too, unless what you are measuring is also isolated in respect to everything else. Get a proper CAT-rated high voltage differential probe or isolate the DUT from mains if you want to measure mains connected circuits. It causes less pain in the long run.

Regards,
Janne

[EEVblog]

I think now that it has become clearer to me what is going to be needed, I will start working on a complete replacement for the PS in the DS1052E and make it so that it will also accept battery input and be efficient. But this is only worthwhile IMHO if it can be done for under $50 or so.

I think it would be a neat mod, just for convenience sake, for low voltage work.
But as others have said, safety with the exposed connections is questionable. So you'd always get people questioning the mod as being dangerous.

I'd like to do that if such a board was available. And yes, I'd do it as a complete replacement board.
Generating those voltages from a battery is pretty easy, just a few SMPS's and a battery charger. Not hard for under $50 in smallish volume. One-off? probably not with a proper PCB.
But then how do you charge it? Still use the IEC mains input? Plugpack? Starts getting a bit messy logistically.

Dave.

[Zero999]

100V of batteries is not a desirable thing though. 50V and higher is inherently a dangerous thing and to be avoided especially if we have less experienced hobbyists read this and want to try it. The other thing is that the linear regulators used after the switching power supply are rather inefficient for battery use.

I think now that it has become clearer to me what is going to be needed, I will start working on a complete replacement for the PS in the DS1052E and make it so that it will also accept battery input and be efficient. But this is only worthwhile IMHO if it can be done for under $50 or so.

The batteries should be in an insulated enclosure, regardless of whether they pose a shock risk or not as there's a definite fire risk if they're short circuited: a fuse is a must.

Why not simply use a switching regulator, if linear regulators suck too much power?

The scope's internal supply should be isolated from the voltage you're measuring, otherwise you could have all sorts of problems with ground loops and short circuits.

I think the easiest solution is to just buy an inverter, that way the battery voltage is isolated from the 'scope supply and you don't have to worry about permanently live dangerous voltages.

The inverter of course will waste some power which will reduce the battery life. You could go with the 100V+ battery solution and connect the batteries in series via an isolator. Attached is an example showing three 48V banks connected in series with two pole isolator between the banks. When the isolator is off, the circuit will be dead and the highest potential difference in the battery pack will be 48V, 58V worst case if they've just been charged.  You could make it even safer by using a three pole isolator and connecting the batteries in banks of 36V.

[Sir Linus]

OK, first post. Hi everyone.

Since the OP requested ideas, here's what I'd do. Not a hack, not cool, not particularly cheap, definitively not technical, but practical, portable and fairly lightweight, not to mention versatile.

Anyhow, the Paul C. Buff Vagabond Lithium is a small 3,5 lb 130 Wh battery with a built-in true sine wave inverter, comes in 230V and 120V flavors for US$240. Photographers use these for location work. Spare batteries are available for US$90, and the inverter can run off any 12V SLA for extending capacity. Fairly lightweight at under 2 kg and versatile. Should run the scope for 2+ hours, I guess.

Check out http://www.paulcbuff.com/vagabond.php

And no, I don't own the inverter (nor the scope), but google finds plenty of positive reviews.

-L

[Lightages]

Yes, the flashes and equipment made by BUFF (usually known as Alien Bees) are well regarded in the photography world. I have experience with his products. I would not hesitate to buy one of the inverters he has listed and it would be useful for many things. If it becomes too much hassle to design and make this battery idea work for the DS1000 then I might get one of these.

But, the scope would be much more portable and flexible in use with its own contained power supply. I will be poking away at it for a while before I get to anything useful in design.

[A Hellene]

Putting some more thought into the project, it seems to be electrically doable:

The PSU PCB can be redesigned, using the original TOP24x-based AC/DC converter design & parts (or removing the low voltage components and adding a daughter-board to the stock PCB) with a few >90% efficient and compact DC-DC converters that include the power stages on chip (3 x SiC413 for the -6V50/+3V35/+6V40 lines and a MAX618+317L for the +15V0 line generation) plus a Pico-Power AVR uC with a few extra SMD MOSFETs and inductors for power management, to supervise and charge the battery, supervise the input/output voltages, control the fan according to the interior temperature and also control the device power state (Manual ON/OFF and Emergency OFF if power not good/ battery failure detected).

Given that Rigol's power consumption is about 11W (or 13W using a USB flash drive), a battery pack of 10V8/4Ah (consisted of 3*(2*3.6V)/2000mAh 18650-type cheap Chinese cells) would be enough for almost four hours of operation per charge; or for five/six hours respectively by using 2500mAh/3000mAh cells. It is only a matter of cost!

But I stated that it is electrically doable because the temperature of the interior, which will also serve as the battery compartment, might be a problem for the good health of the Lithium-ion cells, since most of them, especially the cheaper ones, are designed for operating environments from 0ºC to 50ºC...


-George

[Sir Linus]

Oh well, I love to toss in these KISS ideas...

If George's idea above is electrically doable, how about this for a battery:

http://www.hobbyking.com/hobbyking/store/__14070__ZIPPY_Flightmax_4200mAh_4S1P_30C_LiFePo4_Pack.html

These packs come in most any size of course, as do similar Lipos...

LiFePO4 are supposed to operate at least up to 60°C IIRC, though I don't have the temp specs on this one... and shelf-life should be longer than Li-ion... not very flammable either...

A battery (maybe over)speced to put out 126 A continuously shouldn't be too bothered by a bit of warmth inside the scope... how warm does the inside get during normal operation?

Anyhow, if internal heat is a problem, this pack could very easily be muonted externally with a bit of velcro, and the connector jack could double as a 12 V input... just spraypaint the pack black to look professional... =D External charging would be easy, as well as swapping packs if needed...

-L

[Lightages]

I see two different approaches now.

1. Brute force inelegant mode: Install a cheap inverter inside with the parts scavenged from a $15 12v-110 or220 inverter available on Deal Extreme. Install the correct the size battery inside to provide the inverter with power. Install a switch to change from AC power to Inverter output. Install the appropriate battery charger for the type of batteries installed to charge the batteries while running on AC. Install a power jack to allow running the new inveerter directly form a car battery.

2. Elegant and harder to do: Remove the stock power supply and design and build a drop in replacement that will run from batteries directly, run from AC, and will also charge the batteries.

The thing with option 1 is that it "sticks in my craw". It is so cheap and crude but has the advantage that almost anyone with any level of electronics skill could do with the right instructions. There is also the problem of introducing new electrical noise with the cheapo inverter.

Option 2 would be very rewarding to do and would be more efficient too. But it will cost the most by far. It would also take the longest to accomplish.

A Hellene: I don't see that it could be very practical to try to re-configure the stock power supply. Not much woul be reusable for the lower voltage battery input.

Sir Linus:  The radio control battery idea is probably a good idea as the parts and chargers are available everywhere. Good power density too.

[ivan747]

Here's what I came up with:

12V sealed lead acid batteries, connected to a boost switchmode power supply to provide +100VDC. The scope will take care of the rest.

[Uncle Vernon]

I see two different approaches now.

1. Brute force inelegant mode: Install a cheap inverter inside .............

2. Elegant and harder to do: Remove the stock power supply and design and build a drop in replacement that will run from batteries directly, run from AC, and will also charge the batteries.

3. Replace the the factory PSU with a low voltage PSU, battery and battery charger and power this from a suitably rated power brick.

Not as elegant as option two, but a technically better solution than option one. Disadvantages is the clutter and need to cart another piece of hardware, no worse than option one though. And better for quick job within the scope of a single battery charge.
Advantages, easier to accomplish than two, less heat and less restricted by space constraints.
Suitable Pre-built SMPS should be available off shelf but engineering to house and mount battery still required. Mains wiring still contained within approved device, so device modification wont upset the OH&S fairies where option two would preclude the use of the device on many job sites without an engineers sign off.

[alm]

Mains wiring still contained within approved device, so device modification wont upset the OH&S fairies where option two would preclude the use of the device on many job sites without an engineers sign off.

Really? OH&S doesn't care about defeating safety ground? You'd almost think that OH&S is more about bureaucracy than safety .

[Uncle Vernon]

Really? OH&S doesn't care about defeating safety ground? You'd almost think that OH&S is more about bureaucracy than safety .

The first thing you learn about OH&S is that it has no interest in promoting safety and a real purpose in offloading responsibility further off down the chain.
In real terms a modified instrument that follows best practice in every way will be rejected from use in a workplace whereas any dubious and poorly designed piece of imported crud with apparently authentic approvals will be OK. Such is the power of bureaucracy, someone gets toasted, no bother, the company has a paper trail that says they purport to care and more importantly responsibility can be offloaded to some, usually now defunct, importer who is nowhere to be found.
In practical terms if you want to used a modified instrument in most workplaces, an approved power brick can eliminate a lot of being mucked about.

[Mechatrommer]

i guess this is the earliest thread that menitioned it... anyway sorry for the spam... just a head up for my Battery Powered PSU for Portable Rigol DS1000E/Z to thread followers, cheers.