ammeter

[Johny London]

Wanting to check when my charging current is low (tail current?) and looking for the right ammeter. Was thinking a 500a shunt and a bog standard digital panel ammeter off ebay - but presumably it will need to display + when giving out current and - when charge is going to the batteries (or vice versa?) - it's not clear if the panel lcd/led ammeters do that. Otherwise I presume I'd need a needle type one with a zero centre like on a car?

I know some of you guys have them already and I want one too.

[Richard10002]

I bought cheap ebay meters, volt meter and ammeter, (probably about 20 quid or so in total), which were fine but, in the end, I decided i wanted Amps, Volts, and cumulative Amp Hours, so bought a NASA BM2, for about £125 or so.

A much neater solution, does the job precisely as i wanted, (always remembering to zero the Amp Hour reading each time the batteries are "full"), and I haven't regretted the expense. I learned to take no notice whatsoever of the %age State of Charge reading - it is worse than useless.

[smileypete]

If spending hundreds on batts etc I'd highly recommend getting a 'clamp meter' that can read DC amps, it might save a load of aggro down the line or at least barking up the wrong tree. This would be my pick and £31 is a great price from a UK source:

https://www.amazon.co.uk/Signstek-Handheld-Digital-Resistance-Capacitance/dp/B00V9VL9CC

It would also be a good stop gap and backup for the cheap China sourced meters as they'll take a while to arrive and may be a little hit or miss.

If getting a clamp meter doesn't appeal then I'd have thought it best to go for something like the Nasa BM2 as mentioned, with UK sourcing and backup from the supplier or manufacturer.

 

 

Edited November 8, 2017 by smileypete

[Johny London]

I have a decent clamp/dmm already but didn't think the clamp did dc amps? Previously I was encouraged to get a Smartgauge, which tbh doesn't seem to be a lot of use, now the mood is toward the BM2

Richard - so can I assume the bog standard lcd/led panel ammeters do current each way ie +/- ? If so that is the way ahead for me. I'd rather just have the raw data and work the rest out myself.

[Onewheeler]

Some of the cheap Ebay modules do current in both directions, some don't. Some that do need an isolated power supply, so you would need an extra module for that. This one doesn't: http://www.ebay.co.uk/itm/DC-100V-500A-Voltmeter-Ammeter-Charge-Discharge-Isolation-current-tester-12v-24v/172733947168?hash=item2837bedd20:g:H0YAAOSwbiFZQ6P-

[MtB]

On 08/11/2017 at 10:18, smileypete said:

If spending hundreds on batts etc I'd highly recommend getting a 'clamp meter' that can read DC amps, it might save a load of aggro down the line or at least barking up the wrong tree. This would be my pick and it's a good price from a UK source:

https://www.amazon.co.uk/Signstek-Handheld-Digital-Resistance-Capacitance/dp/B00V9VL9CC

It would also be a good stop gap and backup for the cheap China sourced meters as they'll take a while to arrive and may be a little hit or miss.

If getting a clamp meter doesn't appeal then I'd have thought it best to go for something like the Nasa BM2 as mentioned, with UK sourcing and backup from the supplier or manufacturer.

 

 

 

I have one of those. It is a 'quick and dirty' way of measuring current in a conductor. Despite the three decimal places on the display don't be mislead into expecting it to be accurate. I'd say mine is only good to the nearest whole amp or so. It is heavily affected by stray fields and will commonly read 0.5A or 1.0A with no wire in the jaws. Even after pressing the 'zero' button however many times you like.  

My BMV702 is however, far easier to use and comes with a really long cable so you can put the display miles away from the batteries in your saloon and watch it instead of the telly. And when there is no current flowing it says zero, which I find encouraging.

[WotEver]

7 minutes ago, Johny London said:

I have a decent clamp/dmm already but didn't think the clamp did dc amps?

Some do, some don’t. 

[MtB]

On 08/11/2017 at 10:34, WotEver said:

Some do, some don’t. 

 

Yes, there are two types of clamp meter. The DC ones are significantly more expensive.

The clamp meter recommended above by smileypete is a DC clamp meter.

[WotEver]

8 minutes ago, Johny London said:

Previously I was encouraged to get a Smartgauge, which tbh doesn't seem to be a lot of use, now the mood is toward the BM2

Both of them together are a really good match. The SmartGauge is the best tool for letting you know how discharged your batteries are, the ammeter on the BM2 is the best tool for telling you when to stop charging, and the two tools together (Ah counting from BM, SoC from SG) provide a fast and simple method of calculating the battery capacity. 

[MtB]

On 08/11/2017 at 10:38, WotEver said:

Both of them together are a really good match. The SmartGauge is the best tool for letting you know how discharged your batteries are, the ammeter on the BM2 is the best tool for telling you when to stop charging, and the two tools together (Ah counting from BM, SoC from SG) provide a fast and simple method of calculating the battery capacity. 

 

Given the BM2 also makes a reasonable stab at SoC, it too tells you when to start charging.

Agreed you need to reset it occasionally but it saves spending a further £120 on the SG.  

And bear in mind what you tell me occasionally, that the SoC at which to start charging really isn't critical. 40%, 50%, 60% are all fine.

[Dr Bob]

I bought a panel voltmeter from amazon (less than a tenner) to be the gauge for the water tank meter - and that only shows +ve voltage and not -ve. The spec sheet prior to buying did not give any indication it only did +ve. It may be similar buying an ammeter.

If it were me, I would go for a proper battery monitor and the Nasa looks as good as anything as although Amps in or out is very important, I find looking at the amp counter first thing in the morning to see how much has gone out is an important number and a good cross check on the volatage. Amp hour counter no use when charging once the SoC is getting near the tail current targets.

I like the look of those clamp meters. I think I will get  one! Thanks smileypete!

Edited November 8, 2017 by Dr Bob

[WotEver]

1 minute ago, Mike the Boilerman said:

Agreed you need to reset it occasionally...

Daily, Mike. The errors are cumulative.

By the end of a few days of not charging to 100% SoC the reading can be 100% adrift - a totally pointless indication. That is one of SmartGauge’s main advantages; it gets more accurate with time requiring no user intervention whereas an Ah counter gets more inaccurate every day unless corrected by the user daily. 

[Glynn]

http://en-us.fluke.com/products/clamp-meters/fluke-381-true-rms-clamp-meter.html

[WotEver]

Just now, Glynn said:

http://en-us.fluke.com/products/clamp-meters/fluke-381-true-rms-clamp-meter.html

But that’s silly money for ‘yer average boater’

[MtB]

On 08/11/2017 at 10:51, WotEver said:

Daily, Mike. The errors are cumulative.

By the end of a few days of not charging to 100% SoC the reading can be 100% adrift - a totally pointless indication. That is one of SmartGauge’s main advantages; it gets more accurate with time requiring no user intervention whereas an Ah counter gets more inaccurate every day unless corrected by the user daily. 

 

Yes I can see that, but it's no hardship to press the button every time one recharges to 100% is it?

Where it it trickier is when the batteries are losing capacity. The SG compensates but the BM2 still thinks the capacity is what you set it at, so the % SoC of the real capacity is lower than reported. 

Your comments rely on getting a correctly calibrated SG out of the box though. Mine I'm noticing are very consistent. Nearly always they show a 14% difference in SoC, Right now for example, one says 89% and the other 75%. They move up and down in unison except when charging and the tail current is low. The lower one gets to 97% and never goes any higher. The higher one shows 100% when the tail current gets down to about 10%

[Johny London]

Does anyone know what the display is that Jono has in one of his videos - looks awesome! I can't find which video it is right now so will have to watch them all again.

[Dr Bob]

19 minutes ago, WotEver said:

Daily, Mike. The errors are cumulative.

By the end of a few days of not charging to 100% SoC the reading can be 100% adrift - a totally pointless indication. That is one of SmartGauge’s main advantages; it gets more accurate with time requiring no user intervention whereas an Ah counter gets more inaccurate every day unless corrected by the user daily. 

I dont find this a problem.

If I can fully charge each day, then just press the reset button at the end of the cruise (say 4 hrs motor and 4 hours sun). Simple.

It becomes more difficult in winter as no solar and not cruising 4 hrs a day. Typically we will cruise for 2 hrs a day and then a long stint every 3 or 4 days. I know overnight our useage of 80A is not going to be replaced by a two hour cruise the following day so I know i need to charge more to avoid sulphation. In this situation I dont need anything other than my voltmeter to tell me if it getting urgent to charge. I wouldnt trust my amp hour counter/SoC monitor and cant comment as I dont have an SG and not allowed to buy one. I know I need to charge at any one moment in time as i am not at 100% SoC. If the voltage is down to 12.3V first thing in the morning then it becomes urgent and we will go on a longer cruise. There have been a few sunny days in the last week so I am pleasantly surprised there is still some solar getting in to help. Of course, you need to be thinking of the other inputs, time of day reading the volts, the temp, is solar on?, have the kids been on the boat and use the Nesspresso machine 50 times, etc etc, but usually habit takes over and each day is the same.

It's certainly easier in the summer.

Edited November 8, 2017 by Dr Bob

[Richard10002]

1 hour ago, smileypete said:

If spending hundreds on batts etc I'd highly recommend getting a 'clamp meter' that can read DC amps, it might save a load of aggro down the line or at least barking up the wrong tree. This would be my pick and £31 is a great price from a UK source:

https://www.amazon.co.uk/Signstek-Handheld-Digital-Resistance-Capacitance/dp/B00V9VL9CC

It would also be a good stop gap and backup for the cheap China sourced meters as they'll take a while to arrive and may be a little hit or miss.

If getting a clamp meter doesn't appeal then I'd have thought it best to go for something like the Nasa BM2 as mentioned, with UK sourcing and backup from the supplier or manufacturer.

 

 

Worthe a read:

https://www.eevblog.com/forum/testgear/a-look-at-the-uni-t-ut210e/

[Richard10002]

59 minutes ago, Johny London said:

I have a decent clamp/dmm already but didn't think the clamp did dc amps? Previously I was encouraged to get a Smartgauge, which tbh doesn't seem to be a lot of use, now the mood is toward the BM2

Richard - so can I assume the bog standard lcd/led panel ammeters do current each way ie +/- ? If so that is the way ahead for me. I'd rather just have the raw data and work the rest out myself.

I have an older UNI T clamp ammeter which reads DC Amps.

I cant remember whether the digital ammeters did + and -..... or whether some did and some didnt. I was fairly quick to give up on them and get the NASA.

As mentioned above, with the NASA BM2, (or BM1), and a Smartgauge, it is fairly easy to calculate battery capacity, so I guess that is a reasonable reason to buy a Smartgauge, as long as you dont rely on it to be accurate when it reads 100%!!

[WotEver]

40 minutes ago, Dr Bob said:

I dont find this a problem.

 

40 minutes ago, Dr Bob said:

It becomes more difficult in winter

It’s England. We have a lot of winter. 

Hence, a display which doesn’t go out of sync and gets more accurate with every cycle with zero user intervention is a ‘good thing’ for those of us who are permitted to purchase one. 

52 minutes ago, Mike the Boilerman said:

Yes I can see that, but it's no hardship to press the button every time one recharges to 100% is it?

Nope, not at all. How many boaters charge to 100% daily (especially in the winter)?

54 minutes ago, Mike the Boilerman said:

Mine I'm noticing are very consistent.

Yes, they don’t drift. So if they are correctly calibrated at the factory they’ll stay that way. 

[David Mack]

2 hours ago, Onewheeler said:

Some of the cheap Ebay modules do current in both directions, some don't. Some that do need an isolated power supply, so you would need an extra module for that. This one doesn't: http://www.ebay.co.uk/itm/DC-100V-500A-Voltmeter-Ammeter-Charge-Discharge-Isolation-current-tester-12v-24v/172733947168?hash=item2837bedd20:g:H0YAAOSwbiFZQ6P-

That looks good.

The installation wiring diagrams are shown below.

 

If I want to install this with the display remote from the battery, presumably I can just connect the three 'positive' wires together at the meter and run 3 wires (rather than 5) back to the battery/shunt like this:

[WotEver]

15 minutes ago, David Mack said:

If I want to install this with the display remote from the battery, presumably I can just connect the three 'positive' wires together at the meter and run 3 wires (rather than 5) back to the battery/shunt like this:

Presumably

Let us know how it works please. 

[smileypete]

3 hours ago, Onewheeler said:

Some of the cheap Ebay modules do current in both directions, some don't. Some that do need an isolated power supply, so you would need an extra module for that. This one doesn't: http://www.ebay.co.uk/itm/DC-100V-500A-Voltmeter-Ammeter-Charge-Discharge-Isolation-current-tester-12v-24v/172733947168?hash=item2837bedd20:g:H0YAAOSwbiFZQ6P-

Well spotted.

200A version: (smaller cheaper shunt?)

http://www.ebay.co.uk/itm/DC-100V-200A-Voltmeter-Ammeter-Charge-Discharge-Isolation-current-tester-12v-24v/182623244034

And it has a decent voltmeter built in.

 

ETA: Then again, £2.99 for a 500A shunt, with a free analog meter...

http://www.ebay.co.uk/itm/NEW-DC-0-500A-Analog-Amp-Meter-Ammeter-Current-Panel-Shunt-Resistor/171634940295

Edited November 8, 2017 by smileypete

[croftie]

The meter above needs a shunt. On the listing it gives a link to purchase.

https://www.ebay.com/itm/DC-Current-Shunts-FOR-20A-50A-100A-200A-500A-Digital-LED-Voltmeter-Ammeter-/271729386459?pt=LH_DefaultDomain_0&var=&hash=item3f445563db

follow that link and it gives another ebay listing (different seller) that says "Shipping: Does not ship to United Kingdom"

Suggest this link as its from the meter seller so should be OK

http://www.ebay.co.uk/itm/DC-Current-Shunt-FOR-20A-50A-100A-200A-500A-Digital-LED-Voltmeter-Ammeter-Panel/171906336574?hash=item28066a873e:m:mcV1cAcz-mC1SjelrssYCWg

[smileypete]

If huge accuracy isn't a must, a length of cable can act as a shunt. Won't be as accurate over temperature as the stuff a shunt is made of, mind.

By my reckoning, 22cm of 25mm2 cable should have the same resistance as a 500A shunt. (0.00015 ohms)

Maybe strip some insulation and add a small jubilee clip kinda thing, like a small fuel pipe clamp.

Anyway the real thing is £2.99 so no great hardship.

Edited November 8, 2017 by smileypete