Trying to measure amp draw. What am I doing wrong?

Martinjmpr

Wiffleball Batter
The plot thickens???

So as Verkstad suggested, I used my little device to see if I could pass power through the fuses. Guess what: BOTH fuses seem to be blown.
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But then just for fun I switched on the multimeter (with both fuses removed.) The voltage portion works fine. Without the fuses in place. :confused:
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Which leads me to believe that either (a) the meter is faulty or (b) the fuses are only for the ammeter portion of the multimeter. Maybe the 2nd one is a spare?
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Weird. Anyway, I'll be getting some new fuses tonight and if that doesn't work I'll invest in either a new multimeter or maybe even spring for a dedicated ammeter.
 

Martinjmpr

Wiffleball Batter
What model fridge?
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As a freezer? Or what is target fridge temp?
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How hot is ambient?
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Fridge is an Indel-B TB-41. Target temp is usually 32 or 30 (in my experience, the temp only applies to the coldest part of the fridge, i.e. the very bottom. So 32 on the thermostat generally equals ~ 38 - 40 at the top of the fridge.)
 

john61ct

Adventurer
You'll want to fix your DMM issue, but in the meantime
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Fridge is an Indel-B TB-41. Target temp is usually 32 or 30 (in my experience, the temp only applies to the coldest part of the fridge, i.e. the very bottom. So 32 on the thermostat generally equals ~ 38 - 40 at the top of the fridge.)
True Danfoss, now Secop compressor.

I believe that unit will pull a bit over 3A at 12V while the compressor is running.

What percentage of 24 hours it cycles will depend on (besides your temp setting):

Ambient temps

Any additional insulation

How often the lid gets opened

How full it's kept (fully loaded is best, but let air circulate)

How effectively the install clears hot air from the condenser / electronics area, may well be worth adding active venting for greater efficiency

----
Say it's 9 minutes per hour, 15% of (24*3+) is 12AH per day.

Suboptimal conditions will quickly double that, but I reckon as a fridge you won't see much over 35AH per day, even in very hot conditions.

Of course adding a lot of mass (food and drinks) that isn't pre-chilled will cause the compressor to run a LOT for several hours.
 

Martinjmpr

Wiffleball Batter
Success! Must have been the fuses.

Btw those ceramic fuses are crazy expensive! About $4 each and I got 4 (2 of each kind.)

But hey, it works.
6065d7aee5372984ffcf1a7a2feeeafa.jpg


Then it was time to test it on the fridge.

d5e9870bc13f5ca8325bf99c01f5844b.jpg


As you can see it's drawing almost 5 A. Of course this was under absolute worst case conditions, the fridge hasn't been plugged in for over a week and is at current room temperature of about 65°.

However, at least this gives me a baseline. So now I know how many amps is going to draw under worst-case conditions. The next step will be to cool the refrigerator down using 110 V and then once the refrigerator is cool and running, plug the amp meter in again and see how many amps it draws.

I just want to say thanks again to all the good folks here who helped me. I really appreciate it!


Sent from my iPhone using Tapatalk
 

dwh

Tail-End Charlie
It'll draw 5 amps. It's not like pre-cooling it is going to change the compressor, freon, pipework, etc.

But after pre-cooling the compressor will spend less time running.

So now you get into "duty cycle". Does the compressor draw 5a for 10 minutes out of every hour (17% duty cycle) or for 40 minutes out of every hour (66% duty cycle)?
 

Martinjmpr

Wiffleball Batter
It'll draw 5 amps. It's not like pre-cooling it is going to change the compressor, freon, pipework, etc.

But after pre-cooling the compressor will spend less time running.

So now you get into "duty cycle". Does the compressor draw 5a for 10 minutes out of every hour (17% duty cycle) or for 40 minutes out of every hour (66% duty cycle)?
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Yes, good questions. So is there such a thing as something that will measure (and record) amp draw over a period of time? Something simple, not some super-expensive testing instrument. Just something that will measure cumulative amps drawn, like over a 5 hour period, it used a total of 21 amps, that sort of thing?
 

dwh

Tail-End Charlie
Metering & recording stuff is abundant. Amazon & Ebay a source to see whats available. Search "DC watt hour meter" is a good start.
There is so much inexpensive lowvoltage electro-dohickey stuff now days you wont live long enough to see it all.
Btw, "recording" on most of these inexpensive meters simply displays a running log of power consumed. Usually displayed as watt-hours or amp-hours. Reset to zero is usually powercycle the meter.

Watt he said. (See watt I did there? :) )

The "Watt's Up" is the original. There are tons off cheaper knock-offs.

They come in different amperage ratings - 10a, 30a, 100a, whatever. That's the max amps it can handle flowing through it. I would probably get one with a high rating, like 100a - that way I could use it for testing all kinds of stuff, not just a 5a fridge.


This one can handle 50a continuous, 100a peak

https://www.amazon.com/gp/aw/d/B001...hour+meter&dpPl=1&dpID=41Wv5FTNxJL&ref=plSrch
 

dwh

Tail-End Charlie
It'll draw 5 amps. It's not like pre-cooling it is going to change the compressor, freon, pipework, etc.

Woops. Duh...forgot about variable speed compressors. So um...yea, if you've got a variable speed compressor, pre-cooling might actually lower the amp draw.
 

john61ct

Adventurer
Yes the total minutes it's cycled on per 24 hours will determine AH consumed.

However, at least this gives me a baseline. So now I know how many amps is going to draw under worst-case conditions. The next step will be to cool the refrigerator down using 110 V and then once the refrigerator is cool and running, plug the amp meter in again and see how many amps it draws.
Should not matter which circuit you use, assuming you've got a power supply or battery charger going.

Note an empty fridge will consume more than when it's full, takes a lot more initial energy to cool down the contents (thermal mass) than the fridge interior itself.

Bottles full of water work well.
 

john61ct

Adventurer
Fwiw, Not really correct. Whats described might be an "Amp-Day" while could be used to express accumulated consumption over period of time its quite daft and not used in engineering conventions.

"Amp-hour" expresses accumulated current flow over a period of time. One hour is the time unit.
For example, 1 amp flows for one hour = 1Ah. (Duh ! ) Conversly, 2 amp flows for 30 min. is still 1Ah.
Assume this 'fridge draws 5amp & runs non stop. Same time tomorrow, it just killed 120Ah battery.
AH per day is 100% correct and makes perfect sense.

That 5A load, running average 50% of the time, draws 60AH per 24 hours.
 

john61ct

Adventurer
Sorry, I have no idea what you are trying to say.

Electricity takes up no space, so how do you mean volume?

Amps already have a time element, one coulomb per second, so are an instantaneous measure of current (flow rate, like gallons per hour).

AH are a static measure of quantity, either usage or capacity. Is that what you mean by ?volume?, like a tank of gas is 15 gallons?

For usage, Amps per (time unit) is meaningless. AH per (time unit) works.
 
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