Inverter Warning

[Old.Tony]

For those of you who use an inverter somewhere, I've stumbled into a problem that resulted from the cheap-ass manufacturers that was unforseen but in hindsight, completely expected.

Scenario: I have a 3-way refrigerator in my caravan. When driving, I can't have it running on gas. When run on 12V, the heater element draws power all the time at a low-ish level (just enough to maintain the temperature within). When run on 240V, the heater element draws power at a slightly higher than 12V level via a thermostat and uses it as needed. Obviously, it's preferred to use 240V - so I do.

My fridge draws about 380W under 240V. Aldi sell a 600W inverter for just $59 and I thought superb, let's do it - so I did. It worked fine.

One fine summer's day we're pulling into our intended destination and the fridge has started warming up. Freezer contents not frozen, you get the idea. Inverter still has power, but 240V no longer being supplied. Why? Fuse was intact ...

Well, the answer is simple and makes identifying an appropriate inverter easy. The Aldi inverter is advertised as a 600W unit and in total it can deliver 600W - but when you crack the case and examine the circuit inside, it's actually 12V split via a pair of fuses into two entirely separate 300W circuits.

Yes, it made me angry - including at myself for not considering that they might have used a simpler, cheaper circuit, duplicating it and advertising the whole product as the sum of the two circuits. Labelling the product as a 600W unit gives the impression that you can draw 600W from it for a single device - NOT SO.

I went and spent some cash at Jaycar buying this 600W unit (1500W peak, no issue there since I'm not driving a compressor). Notice that it only has ONE output. Perfect - it must be able to deliver 600W to a single device then - and that's what I need.

Cheaper isn't always the best.

 

[308bever]

how much was the jaycar one tony?

 

[Old.Tony]

$129. Over double the price, but guaranteed to deliver the power. When it's something as important as the fridge, it's a small price to pay especially when you're heading into the outback.

 

[happy john]

Interesting find Tony thanks for sharing, I've had one of those for a few years now and so far it's been ok. I dare say the ratings are very misleading, most of the Aldi specials are rebranded from well known companies. Nobody appreciates sordid milk either.

 

[308bever]

alright tony, you`ve gotta help this fitter out that has a crack at understanding sparkie stuff... if i have a cigarette lighter socket in the back of my ute running a 90w 3way fridge, can i plug this inverter into that and get colder refridgeration? the socket piggybacks off my 6mm wiring for the anderson plug that sometimes plugs into the van to maintain it`s 100AH battery.

 

[308bever]

would the 150w inverter be all i`d need?

 

[happy john]

Where are you reading 90watts? AC or DC?. That seems very low for a 12 volt element in a 3 way, most of the smaller Dometic fridges draw up to twice that. Is yours a Chescold?.

 

[MANNING]

Unforseen but in hindsight, completely expected.

Always in hindsight, it's an amazing thing.
Thanks for sharing.
Would there be another ( or easier ) way to tell the good from bad besides the price or the single outlet?

 

[Old.Tony]

Price isn't always a good indicator that something's not suitable. I still have an Aldi inverter in the tub of my car to handle the load of the Engel while I'm driving - about 30-40 watts required. I'm going to approach it like this: unless the documentation for the unit actually says what the max load per outlet is, I'm going to assume that max load per outlet = total continuous capacity divided by the number of outlets.

If you're keen to crack one open and have a look - see if the cables running to the back of the outlet all come from the same source on the circuit board, or if one outlet has its wires connected to a different part of the circuit to the other outlet. In the Aldi inverter's case it's simple - the inputs are joine together (of course) but everything from there on is split and identical across the centreline of the circuit board, almost like they simply joined a pair of 300W circuits onto one board. Naturally if the outputs are all connected to the same part of the board, you can get the full output from the inverter from either outlet.

90W is 7.5A which would be about right for a 30L or smaller 3-way fridge and yes, a 150W inverter would do the job and as a bonus it's cheap to replace.

 

[308bever]

thanks tony, it`s a gasmart 35 happyJ. just a fridge, might upgrade to an engel fridge/freezer later.

 

[fzrr]

On the topic of inverters. What size inverter would be recommended to be able to recharge drill batteries with the normal mains charger that comes with the kits??

Milwaukee doesn't appear to make a 12v socket charger.

 

[Boogieboots]

My Makita is a 60w charger. I used a borrowed 150w inverter to charge bats for my torch and chainsaw last time I went camping and it seemed to go ok. I dont know if pure or mod sine wave is req though and I didnt check to see what the inverter was...probably should have.
Check the bottom of your charger because my original is 60w but I also have a high speed charger with a fan that is around 200w I think

 

[Old.Tony]

Even the "1 hour charger" for Ryobi's 5Ah battery is going to use 18V * 5A = 90W plus a little for the circuit - say 100W - so one of those 150W jobs will be enough. If you could get a 300W unit for only a few more shekels then choose the larger, it won't be working anywhere near as hard.

 

[308bever]

ebay seems to have 600w(1200w peak) for 60-70 bucks and they have good reviews, would i need to hard wire one of those or would it run through a 20amp ciggie plug?

 

[Old.Tony]

You wouldn't draw its full power through the ciggie plug, you'd trounce the fuse. 600W constant draw is a mere 50 amps at 12V (12 * 50 = 600). At peak load it's asking for 100A and no, the ciggie lighter is going to melt.

Inverters of this size need decent cabling. 8Ga is a minimum - but really you should be looking at 4Ga.

 

[boostin_7]

Ive been told pure sine wave is what you want if you're regularly using it to charge batteries.
Apparently using mod sine wave kills them prematurely????

In regards to cheaper Inverters, ive been using a 2000w 8zed inverter for around 5-6 years now. I use it every day onsite to mix my plaster with a 700w mixing drill.

 

[Old.Tony]

Electric motors like pure sine wave but because they're just big mechanical things modified doesn't hurt them at all. It's electronic circuits that are the bigger issue. Computer power supplies usally use a specific kind of power conversion called "switchmode". AC comes in, is immediately rectified producing somewhere over 300V DC and is turned on and off (switched) by a circuit so that a step-down transformer is able to bring the power down to a nice 12V and 5V smooth pure DC that the computer circuits will like.

Because the bridge rectifier at the start of the circuit is just a bunch of diodes with some heavy duty electrolytic capacitors, there's nothing there that's going to object to modified sine wave.

So if your battery charger employs a switchmode power supply (eg C-Tek) the output stage has no idea what the input is like and the battery is treated the same regardless.

If the charger uses a more primitive power supply then it could have an impact on the charging circuit but these days that'd be pretty rare. Switchmode supplies can fit into those small adapter packs for your phone nowadays.

 

[fzrr]

Even the "1 hour charger" for Ryobi's 5Ah battery is going to use 18V * 5A = 90W plus a little for the circuit - say 100W - so one of those 150W jobs will be enough. If you could get a 300W unit for only a few more shekels then choose the larger, it won't be working anywhere near as hard.

Cheers it's says 90w on the bottom of the charger so I'll look for a 300w. My experience with inverters is limited.

I remember buying a cheap one for use with a laptop and it would only ever charge the laptop when it was switched off. As soon as you turned it on it would start the warning beep.

 

[DVR]

Have you all considered the inherent risks of using and inverter while traveling? I was researching the best way to run my 3 way fridge after finding one at a garage sale. Google it and you'll find a lot of talk about people, even here in Aus, have been electrocuted (dead) after their vehicle was involved in a collision and the car got hooked up. There are no safety's built into them to protect you should the worst happen.

My research found that in the end, the only problem with the 12v on a 3 way was voltage drop caused by the undersized cabling and cig plug connector that seems to be used across the board by all the manufacturers. Doing away with them and replacing them with some H/D cable, hard wired into the fridge and a suitable H/D plug solves the problem. This it the way I went, with a 2 pin low voltage plug mounted next to the aux battery in the tub of my NAV. Not easy to do in a caravan, granted.

Of course its your choice, but man, concidering the risk I think it's a no brainer.

 

[happy john]

Hi DVR, I'd use the term "no brainer" to refer to the morons that run their 3 way on gas as they travel and fuel up, due to the fact their fridge has been poorly installed and wired this is the path they use.

You'd have more chances being trapped in a burning car with a fire started by 12 volt than electrocuted by a 600watt invertor in the tub. The 3 way is on the way out now, due to the reduction in price of solar and soon Lithium compressor is the way to go.

No more sordid milk or hot beer to worry about too. Have you a link to these electrocution claims?, I've never heard of it.

Cheers