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Peaklander

Measuring amps from alternator or solar panel

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Hi, wondered what advice and experiences people have about fitting an ammeter to their vehicle? I want to measure the input to my batteries and probably the current drain from my aux that feeds the fridge, heater and camping lights.

There are four choices I think and I haven't used any of them previously.

 

1. Wire-in a meter that sits in a main cable - this is inflexible and very spendy if you go for Blue Sea which I believe is top quality. There's probably cheaper stuff but the measurement range is probably lower.

 

1469202356_Screenshot2019-12-04at17_07_13.thumb.png.c01e76929df68b81f20ace7e1e41eaae.png

 

 

2. Buy a shunt 'kit' from China for a few £ - this needs the shunt wiring permanently in the desired cable and then the ammeter (volts measurement translated)  sits across this. Advantage is that the meter can be mounted remotely (like in the dash)

 

3. Buy a Hall effect sensor and meter for lots of ££ - advantage is that the sensor can be opened-up to re-clamp a cable of your choice., The meter can be remotely mounted.

Here is an example of this:

1495620524_Screenshot2019-12-04at16_54_50.thumb.png.a971a49ccd1dfb8c7b58d84a5acca818.png

 

4. I suppose another option is to buy a clamp meter but for DC these are spendy too!

 

So as I say, what do you have and what advice can you offer?

TIA

Edited by Peaklander

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We have a Fluke clamp on Amp meter IF we want to know amps and have no idea what sort of amps we'll find..

I have a "thingie" that you put in the fuse holder, fit the original fuse in and it will show the amps in a small display.

Cheap and works quite well when chasing currents..

Shunts etc. require good knowledge of electrics and getting it wrong can give interesting results.

My "Minus40" fridge/freezer can show the drawn amps in the display.

However, why is it you'd like to know this ?

 

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Not that I might be tinkering with something along these lines :ph34r: but curious as to what people consider a reasonable price for a trustworthy / quality 52mm battery volts AND amps meter using hall-effect sensor (so no shunts, and capable of measuring 1000A)?

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Ah yes the Blue sea one has a shunt. I should have guessed really. There must be a link that I missed so thanks @Red90 for that.

@Arjan I think that it would be useful to fairly easily measure feed into my batteries when on a trip. I have mentioned elsewhere that this summer we just managed with high heat and the 100W solar panel and then in the autumn with little solar charge the heater drain was noticeable.

There’s a lot of power available from the alternator when travelling but really I want to be in possession of more data about what’s happening and especially on the solar side. It’s really tricky trying to decide shade or sun. A portable panel would sort that but I’ve done enough trips now to not really want to be moving it around.

Also I have long suspected that my  alternator should be upgraded. This has been noticeable in the last few weeks when lights, blower, heated mirrors, heated front and rear screens all on simultaneously, pulled my charging volts right down below 12. So I have just fitted a 100A with a big cable back. 
 
So really it’s to get better data and also flexibility of measurement, hence the Hall Effect one that caught my eye. I just can’t find one that looks as ‘attractive’ in Europe.

As for wanting to measure up to 1,000A @FridgeFreezer, did I read that correctly?!🤔

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Does not your solar charge controller not show amperage and power production?  As far as producing adequate power when not driving, you need to sit down and work out the math for average daily power production and usage.  This let's you properly choose the solar panel and battery sizes.

If you want to monitor all this, you want a power meter that tracks usage and can then show you daily numbers.  For most normal camping items, this can all be done with a decent solar charge controller by connecting the loads to its load terminals.

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45 minutes ago, FridgeFreezer said:

Not that I might be tinkering with something along these lines :ph34r: but curious as to what people consider a reasonable price for a trustworthy / quality 52mm battery volts AND amps meter using hall-effect sensor (so no shunts, and capable of measuring 1000A)?

What sort of cable run are you using?

Not using hall effect but we've built and bought plenty of LCD based things from the likes of Farnell / RS and put them into the digger and tractor for checking the alternators etc., are working. We haven't bothered with hall effect sensors because you usually get plenty (read enough) of a voltage drop across the cable itself. So measure the resistance of the cable accurately and use that for calibrating the gauge and away you go. No need for extra shunts and/or hall effect sensors.

I'm sure a man of your skills @FridgeFreezer can whip up something with a little micro-controller easily enough.

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Was thinking about this, accumulative watt meter would be far more use, you would know exactly what had gone in then, over say a day, and then it resets.... Or something. 

I expect fridge has this sort of thing kicked with an arduino and a couple bits of string.... 

As for combined volt/ammeter.... For a quality featured item, new in the shelf as a full kit they are going to be £150 all day for retail. 

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Lots of low cost stuff available, but like I say, you should have it on your solar charge controller.  If you are not using a charge controller, that will be a bunch of the charging issue.

https://www.amazon.co.uk/CPTDCL-Digital-Multimeter-Voltmeter-Capacity/dp/B07Q2Q6G8L/ref=sr_1_13?keywords=dc+watt+meter&qid=1575490336&sr=8-13

https://www.amazon.co.uk/s?k=dc+hall+effect+ammeter&ref=nb_sb_noss

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I don't want to get into any "why are you using that controller?" discussion because it's been done to death in other threads. Suffice to say I am using the cTek controller that provides a charge for the aux battery and sometimes a trickle for the engine one. It doesn't provide visibility of volts or current. I monitor the voltage across both batteries with a panel mount voltmeter and using a toggle switch I can flip between them. So I have some idea about what's happening but not much.

I could do the maths but the problem is that there are assumptions to make that will produce a very wide estimate. Take the 100W solar panel for example. Working blind I don't know what it is producing - I can only see the voltage output from the cTek and have no idea about power going in. That's why I need some more data and hence this thread.

@Bowie69 back in the day I could and did programme 8bit microprocessors in assembler (for a living for a while) but the Arduino has passed me by. Maybe that would be a project in my retirement but I would need a steer.

@Red90 I will click your links when I get chance - thanks

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Cheers @Peaklander, cut my own teeth on 6502 assembler and even machine code for a while, now quite heavily into Web stuff, like you though, arduino has passed me by.

 

 

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4 minutes ago, Peaklander said:

@Bowie69 back in the day I could and did programme 8bit microprocessors in assembler (for a living for a while) but the Arduino has passed me by. Maybe that would be a project in my retirement but I would need a steer.

To be honest the Arduino doesn't need much of a steer. There's plenty of code available, they've done a pretty good job at making it accessible for everyone (including kids). However, if you've got some prior experience of micro-controllers might I suggest the STM32 range of micros. The Arduino's have become quite expensive for what they are and there appears to be an ongoing battle between "Genuine" Arduinos and clones.

For half the price of a genuine Arduino you can get an STM32 Nucleo that is of the same form-factor (a wonderful decision on their part) and are compatible with the Arduino shields, except that you get a full-blown ARM core with far more functionality. You can also program them using the same environment but should you want to move to something more advanced then that's easy enough (things like the mbed OS for example) or hard-core like myself and doing it all from bare-bones and at the command line.

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17 hours ago, Peaklander said:

As for wanting to measure up to 1,000A @FridgeFreezer, did I read that correctly?!🤔

You did - but you can use different versions to give a bit more resolution, +/-200A might be enough for most uses I guess.

Would it be useful to have a battery monitor that logs data to an SD card say once per minute or 10 minutes? House & vehicle battery volts & amps perhaps into a .csv spreadsheet file? Not that I've thought about it... ;)

@Bowie69 I don't do Arduinos, mostly STM32 these days.

 

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18 hours ago, FridgeFreezer said:

Not that I might be tinkering with something along these lines :ph34r: but curious as to what people consider a reasonable price for a trustworthy / quality 52mm battery volts AND amps meter using hall-effect sensor (so no shunts, and capable of measuring 1000A)?

£1.99 but only if it lights up blue!

Logging would be handy if you could easily move it between cables so that you could test a device individually / find a leak / see how hard a fridge is working day and night and so on. Log date & time, voltage and current draw and be unobtrusive enough to be able to leave in place whilst driving around. Maybe a low battery alarm too so you could set it for "your car won't start if you draw any more power" or "your going to kill the battery if you draw any more". Or if you wanted to get really funky a "based on your current consumption your battery will be flat in... hours"

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Can my order be first on the list? I'd pay more than £1.99 too.

Haven't had time to read about the STM32 yet, I will though. My first question would be how would you interface with the measurement device? Does it have an analogue input or is there an interface that talks back somehow. I could start reminiscing about 6502 and how to do it but things have moved on...

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The STM32s have a number of analogue inputs. What we've done in the past is simply measure across the cable, you don't usually need a potential divider then because you're only measuring mV. Provided the ADC can be floating with respect to ground.

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Sensor is on its own little board with a 4-wire interface for robustness / EMC. You can chain up to 4 sensors.

If there's serious interest we could make a few but they're not cheap because they're using decent bits rather than whatever's cheap from China. Also a gauge housing is a PITFA to produce in small quantities.

Anyway, this is what I'm fiddling with;

20190912_164938w.thumb.jpg.8a785f85700d9d7f179af4802efac01d.jpg

 

 

 

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Looks great, be impressed if you got away with charging, at cost, less than £100, if you included your labour at even a modest rate.

Is one of those ali rings where you got your stalk clamp for your 109 from?! :) 

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Here's a little video shot very shakily in the ambulance by night...

It shows in sequence:

  • Ignition ON (-11A draw on main battery) and fridge running (-4A draw on house battery)
  • Engine cranking (-225A out of main battery, 10.9V terminal voltage)
  • Engine start (+30A into main battery, alternator providing 14.1V) split-charge not yet engaged
  • Split-charge kicks in (+15A into main battery, 37A into house battery, alt volts drop to 13.8V, 0.6V goes missing across the split-charge/isolator)

Ignore the extra voltage reading at the bottom, that's an uncalibrated ADC reading for the 12v ignition live supply into the gauge itself - the sensor heads use a more accurate ADC and precision reference.

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21 minutes ago, Bowie69 said:

Looks great, be impressed if you got away with charging, at cost, less than £100, if you included your labour at even a modest rate.

Is one of those ali rings where you got your stalk clamp for your 109 from?! :) 

It's a different lump of ali from my random collection of lumps of ali :lol: buying stock "just in case" adds up really quick so you've gotta grab offcuts where you find 'em!

Depending on numbers it *could* be bought in under £100, tooling up is the hard part and below a certain volume it's all hand-made. If you plan to make (say) 100 units it all gets easier because you can automate a lot and get volume discounts on the few pricey components.

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That's really good. Just what's needed. Can you share more details like the hall effect sensors and also that nice programmable display? Does the STM32 drive that directly and you write code to address it and produce what you want?

I would like to read more around how you do this.

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16 hours ago, Peaklander said:

That's really good. Just what's needed. Can you share more details like the hall effect sensors and also that nice programmable display? Does the STM32 drive that directly and you write code to address it and produce what you want?

Well, yes and no - we made the whole thing as a bit of a side-project. You can't buy "the nice programmable display" as such, I designed the PCB & wrote the code for it (and made the housing) - the display screen is a standard round OLED. The current sensors are quality industrial hall-effect ones but on a custom board with an ADC and precision voltage reference plus drivers to give a reliable connection over long cable runs

I was really just posting it here to see if anyone might be interested in it as a decent quality battery monitor although the basic board could do any number of other things. As it stands it could easily control a split-charge relay or be almost any sort of dashboard gauge.

If there was enough interest we could make a few.

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Only just seen this topic, not on here as often nowadays. I'd be interested in one of these if you did get around to producing them.

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