Using rigol DS1052E with Kensigton inverter

[truhlik_fredy]

I have this cheap Kensigton Car Inverter



I think I should be OK with Wattage rating, mine is about 75W - 100W continuous rating. I'm not 100% sure, it's inside the car and I installed it under the dashboard 3 years ago and I don't want to take it apart if anyway I couldn't power the DSO with it. From the specs datasheet the Rigol should take less than 50W so I should be OK with that. My only concert is that the inverter is making square wave AC and I'm not sure if I will damage the oscilloscope with it and even when not if the measurement won't be distorted. For example when I powered laptop from the inverter and tried to play music it made very much noise. I think it's because the higher harmonics in the square wave. So now I'm afraid to use it with me measuring equipment. Have anybody experience with that?

Thank you. Anton

[Simon]

You will be fine with it. the output waveform is not a problem, the SMPS in the rigol is going to rectify the inverters output to DC anyhow and is a DC/DC converter anyhow.

If the inverter is a decent one it will have short circuit protection anyhow

[Mechatrommer]

afaik, only ac motor will be affected, most home appliances will reconvert anything ac back into dc (with proper circuit, not elcheapo half bridge rectifier or such), so should be fine. my speculation about your noisy laptop music, is due to harmonics through air, not through the power supply, just like when you put "calling" handphone near your pc or speaker. now, with this idea, make me think if possible to measure mains with the dso connected to inverted battery supply. iirc, some suggesting, its not possible and dangerous, but i cannot (or too lazy) find the reference back.

[Simon]

your problems with sound on the laptop may be due to the circuitry of the amplifier in the laptop picking up the inverters interfearance over the air rather than through the power line

[truhlik_fredy]

Thank you very much, now I'm more confident

I think the inverter itself is rubbish, el cheapo. And I'm wondering why have people such high option on Kensigton brand, I think it's not good. There is fuse, but I think no other protection. Once inverted polarization on input and device was dead, it was replaced in the shop from where I got it without any question asked, but it was because of very stupid staff, but I wan't complaining

In meantime I have proper pure sine device 1000W constant and with much higher peak. Just it will be more complicated to install it into car (even temporary), so at the moment I'm holding it back and trying using the old one till I can. I wanted measure 3 signals in the car and thats it. So I could hold back installation of new inverter little longer.

The noise I think similar to the one who somebody described to me when he got cheap car charger for cellphone and connected cellphone o the car radio while charging. Not purified DC-DC or pulse power suply with huge spikes.

If it's picked by air then I could find out with small experiment. Laptop powered from battery inside car and something powered by inverter to make a load should make same results as I described before?

And about the batteries, in the shed I have 3 weak batteries (not good for car, but still usable when you require much lower voltages) and I was thinking to recharge the best one from them and with 1000W pure sine inverter measure some stuff. Good you mentioned it, I almost did it Thanks again.

[Fraser]

Hmmmm... cheap inverters = nasty harmonics = risk to equipment performance and/or reliability

A high quality inverter for 12V to 110V or 220V will normally use a 'modified sinewave' or a fully synthesised sine wave. Any inverter that produces a square wave output is fit only for non critical applications that involve transformers or resistive loads. Square wave inverters generate masses of RFI and harmonics that are really bad news for SMPSU's and any sensitive electronics. They can be tamed with a quality Low Pass Filter but it's size tends to mean manufacturers don't use them. Bear in mind that these cheap inverters can also generate some pretty hefty voltage spikes and your car power rail is equally capable of carrying spikes and you end up with a piece of kit that has the potential to damage sensitive equipment and even if not so serious, it can effect performance. Many inverters for laptops are designed to be very compact and often compromise on output waveform purity, such are best avoided for use with sensitive electronics.

My best advice is to use a quality modified sine wave inverter.... it may cost a little more but it's worth it. If you connect a mini hi-fi or radio to the inverter and you hear nasty noises coming from the speaker... it's not a good inverter.

As a final comment.... Inverters and UPS's are a known high fire risk item in my industry so should be used with care. An inverter should never be permanently connected to a cars supply even if it is a self starting, low standby current model. Cheap 12V-110/220V inverters often have little, if any, protection against fire caused by a fault....a 20A input fuse just isn't good enough.

Just my 2 cents worth but I have used most types of inverter and UPS technology and cheap or very compact usually isn't good in either case  

[NiHaoMike]

It shouldn't damage anything but the EMI might be enough to make measurements unusable.

[Mechatrommer]

i measured (roughly characterized) the ac output from some of my inverter and ups'es. its not square, its some nasty arbitrary spike/shape at proper 50Hz (our mains). elcheapo i think, the pure sine wave inverter is expensive.

[Simon]

what about rectifying the inverter's output to DC with some hefty filtering ? after all the scopes SMPS is a DC/DC converter

[truhlik_fredy]

A high quality inverter for 12V to 110V or 220V will normally use a 'modified sinewave' or a fully synthesised sine wave. Any inverter that produces a square wave output is fit only for non critical applications that involve transformers or resistive loads. Square wave inverters generate masses of RFI and harmonics that are really bad news for SMPSU's and any sensitive electronics. They can be tamed with a quality Low Pass Filter but it's size tends to mean manufacturers don't use them. Bear in mind that these cheap inverters can also generate some pretty hefty voltage spikes and your car power rail is equally capable of carrying spikes and you end up with a piece of kit that has the potential to damage sensitive equipment and even if not so serious, it can effect performance. Many inverters for laptops are designed to be very compact and often compromise on output waveform purity, such are best avoided for use with sensitive electronics.

My best advice is to use a quality modified sine wave inverter.... it may cost a little more but it's worth it. If you connect a mini hi-fi or radio to the inverter and you hear nasty noises coming from the speaker... it's not a good inverter.

As a final comment.... Inverters and UPS's are a known high fire risk item in my industry so should be used with care. An inverter should never be permanently connected to a cars supply even if it is a self starting, low standby current model. Cheap 12V-110/220V inverters often have little, if any, protection against fire caused by a fault....a 20A input fuse just isn't good enough.

Just my 2 cents worth but I have used most types of inverter and UPS technology and cheap or very compact usually isn't good in either case  

Exactly that why I got proper pure sine inverter, I was sick when I realized it was square wave (in specs it's not mentioned intentionally, so you have to hope that's pure sine), it wasn't out of the blue, but square wave wasn't clarified properly and I bought the cheap one first. The new one is heavy duty, bulky, big heat sink, everything properly made, switches, sockets, more rugged than the ultra light & small & cheap Kensington etc... And I know it wasn't cheap but it was worth it, but now it's at home and installing it into car will take a lot of time. No garage in 20 miles radius, car on street (here are houses without any driveway or garages or something), rainy weather and I need to make new connections from battery into passenger cabin through firewall, so it's complicated right now to have it working. But I have the square wave inverter working in car and now I'm deciding if the measurements will be delayed by a month to have pure sine inverter or I will have measurements done in less than 10minutes, but DSO will be connected to square wave inverter.

PS: Don't worry, it's in a car, that doesn't means it's always on power supply. I made separate power line with mechanical switch so 99.999% is it like it wasn't there at all. (I don't use it very often)

[Zero999]

your problems with sound on the laptop may be due to the circuitry of the amplifier in the laptop picking up the inverters interfearance over the air rather than through the power line

Interference can be conducted through the power lines which is what I suspect is happening here.

Yes, I agree it should work but there'll probably be interference.

A high quality inverter for 12V to 110V or 220V will normally use a 'modified sinewave' or a fully synthesised sine wave. Any inverter that produces a square wave output is fit only for non critical applications that involve transformers or resistive loads.

A decent inverter will always be pure sine wave. I wouldn't spend good money on a cheap modified sine wave inverter and wouldn't touch a squareqwave inverter with a barge pole, assuming you can even buy them these days, probably not.

I suspect the inverter gives a modified sine wave output rather than a square wave because it's not much harder to do, it probably uses an MCU anyway. A squarewave with the right RMS voltage to power a resistive load won't power an SMPs because the voltage is too low and a square wave with a high enough peak voltage to power an SMPS will blow a resistive load such as a light bulb. For example, suppose the SMPS and light bulb are designed for 110V, the SMPS will require at least 140V peak to work but a square wave with 140V peak also has an RMS voltage of 140V which would blow a 110V bulb but and a 110V RMS squarewave has a peak voltage of 110V which is too low to power the SMPS. This is why it will be a modified sinewave with both an RMS voltage of 110V and peak votlage of 155V so it can power both an SMPS and a light bulb.

what about rectifying the inverter's output to DC with some hefty filtering ? after all the scopes SMPS is a DC/DC converter

You could probably hack the inverter.

The inverter has a DC-DC converter to boost the battery voltage to something near the peak mains voltage, followed by an inverter which converts it to AC. All you need to do is remove the inverter and power it directly from the DC bus although that might be where the noise is coming from.  Perhaps you could

[Fraser]

Hero999,

I concur... my message stating:


"My best advice is to use a quality modified sine wave inverter"

should have read:

"My best advice is to use a quality sine wave inverter". 

Thanks for spotting that error  I will correct my Message.

[rossmoffett]

I've blown up a couple of battery chargers for cordless drills now using automotive inverters.  I'm not sure of the root cause because I just bought new ones and haven't repaired the broken chargers yet, my boss tells me harmonics are to blame.

I also recommend that you only plug it into a true sine inverter.  They're pricey though, fair warning.

[truhlik_fredy]

I've blown up a couple of battery chargers for cordless drills now using automotive inverters.  I'm not sure of the root cause because I just bought new ones and haven't repaired the broken chargers yet, my boss tells me harmonics are to blame.

I also recommend that you only plug it into a true sine inverter.  They're pricey though, fair warning.

Just feedback:

I had one pure sine, the problem wasn't money, but complicated installation at that moment. But then I went trought the troubles and my pure sine inverter blows, without any load, just after 15seconds after I pluged it in, polarisation was OK but the inverter wasn't used for 2 years so perhaps got lose. Then I opened it and one small cap is blown, but it was hell of shot . I will try to replace it, but I think te root is somewhere else. So then I tried the square sine, first it didn't powered up, I think it triggered the shortcut protection, it took too much when powered up. So then I left the DSO switch ON and then turned on the inverter, after that it was working and quite well. Yes there was distortion as I expected (so the power supplies won't rectifier the garbage what the square ones makes), but I was able to measure what I wanted to.

[hacklordsniper]

Just a quick note. The power company was changing pig pole transformer in my street, and released the HV on the LV cable going to houses. ALL of the electronics and devices on this street blew up, literally! I was lucky i was just finishing building my house and did not move any of my equipment in it. The only thing i lost was a completely new Vaillant condensing heating / hot water unit.

This is why i power everything in my lab from a Sinergex PureSine2 Inverter which is powered by a GEL battery which is charged by battery regulator which is powered by SMPS that i designed and sun. The only thing that can happen in case of mains failure is the exploded SMPS which is easy to fix, cheap to remake. Neither of my equipment has any problem running from this inverter...

Here you can see the Inverter, FlexMax60 and the wiring cabinet. The SMPS was still not there at that time... http://hacklordsniper.com/Slike_projekata/Projekt_(1)/Radna%20soba/Slika%20(6).JPG

[truhlik_fredy]

This is why i power everything in my lab from a Sinergex PureSine2 Inverter which is powered by a GEL battery which is charged by battery regulator which is powered by SMPS that i designed and sun. The only thing that can happen in case of mains failure is the exploded SMPS which is easy to fix, cheap to remake. Neither of my equipment has any problem running from this inverter...

Ouch, but still it won't save you things. For example when your house will be hit by lighting...

[hacklordsniper]

Ouch, but still it won't save you things. For example when your house will be hit by lighting...

Not likely since the house has lighting protection. And if in some case lightning comes in power line its not a problem also since the system is on-line (connected to utility power) only in case of low sun insolation, empty battery or high power draw and its done automatically. Also there is a low risk even if it happens in on-line condition because its should progress trough 2 isolated switchers (220 VAC -  48 VDC first) then the 48 VDC - 12 VDC MPPT charger (which is isolated) and finally a inverter which is galvanically isolated. I doubt anything would happen.

[saturation]

Exercise care running a DSO from an inverter.  

The power output isn't a big problem unless its totally off, its the grounding.  If you run this off a car, the car isn't grounded and the scope's inputs float.  Even if you grounded the car, the ground terminal of the inverter may not be grounded, you'll have to check.

Its one reason to have a portable scope designed to have floating inputs, to avoid having to think about such things.

[truhlik_fredy]

Exercise care running a DSO from an inverter.  

The power output isn't a big problem unless its totally off, its the grounding.  If you run this off a car, the car isn't grounded and the scope's inputs float.  Even if you grounded the car, the ground terminal of the inverter may not be grounded, you'll have to check.

Its one reason to have a portable scope designed to have floating inputs, to avoid having to think about such things.

I noticed something strange about ground when I was installing it. I think the ground on AC was different than DC ground. It was strange I didn't understood the reason for it.

[truhlik_fredy]

Not likely since the house has lighting protection. And if in some case lightning comes in power line its not a problem also since the system is on-line (connected to utility power) only in case of low sun insolation, empty battery or high power draw and its done automatically. Also there is a low risk even if it happens in on-line condition because its should progress trough 2 isolated switchers (220 VAC -  48 VDC first) then the 48 VDC - 12 VDC MPPT charger (which is isolated) and finally a inverter which is galvanically isolated. I doubt anything would happen.

Somebody told me that in bad case scenario the current going down make such big magnetism field that even when the device is unplugged will induct inside itself just from that field.

[Zero999]

Not likely since the house has lighting protection. And if in some case lightning comes in power line its not a problem also since the system is on-line (connected to utility power) only in case of low sun insolation, empty battery or high power draw and its done automatically. Also there is a low risk even if it happens in on-line condition because its should progress trough 2 isolated switchers (220 VAC -  48 VDC first) then the 48 VDC - 12 VDC MPPT charger (which is isolated) and finally a inverter which is galvanically isolated. I doubt anything would happen.

Lightning spikes can still be transmitted up the earth conductor and shock you. There's virtually no way to 100% protect you from lightning  Using inverters and SMPSes is not the best way to do it, apart from being very expensive, it's also inefficient; you loose between 10% to 30% of the power depending on the quality of the components and the loading. Galvanic isolation can be achieved by an inexpensive, highly reliable and efficient isolation transformer and overvoltage protection can be achieved using MOVs.

[hacklordsniper]

Lightning spikes can still be transmitted up the earth conductor and shock you. There's virtually no way to 100% protect you from lightning  Using inverters and SMPSes is not the best way to do it, apart from being very expensive, it's also inefficient; you loose between 10% to 30% of the power depending on the quality of the components and the loading. Galvanic isolation can be achieved by an inexpensive, highly reliable and efficient isolation transformer and overvoltage protection can be achieved using MOVs.

I agree with your points, but here is where i disagree. The inefficiency of SMPS is not cared about since it saves lives of equipment altogether worthy 10 times more than is increase in electric bills. And SMPS are definitely not expensive, especially if you buy them.

The second point is that this system is not designed to protect from lightning, but from very often line failures, blackouts and voltage fluctuation. Basically its just a on-line UPS which is built from "blocks" of components and is upgradeable. True on-line UPS costs many money, its not upgradeable and in case of failure i would need to exchange it or do very hard troubleshooting and has no support for solar power.

This the system goes like this:

Line-SMPS-MPPT charger->battery->sine wave inverter with solar power between SMPS and battery by use of transfer solid state relay.

Every piece of this block is "stand alone" and can be easily replaced or upgraded for more/less power without changing the whole system. I hope i managed to explain it more clear now