Low price battery monitor with a 350A shunt (1 Viewer)

Two on Tour

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While hunting around YouTube this afternoon I came across a guy reviewing a cheap Chinese battery monitor with a 350A shunt.

I found it for sale on the UK Amazon site for £37.50 including delivery.

Amazon product ASIN B07CTKMLVD
battery monitor 1.jpg

battery monitor 2.jpg



Here's the guys review of the battery monitor.

 

Stealaway

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Jan 8, 2013
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A cheap digital voltmeter will tell you all you need to know about the batteries state of charge without all these setting and expense.
 
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Two on Tour

Two on Tour

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A cheap digital voltmeter will tell you all you need to know about the batteries state of charge without all these setting and expense.

Well bully for you with your cheap digital voltmeter, some of us like a bit more sophistication and toys in our pride and joy. ;)
 

hilldweller

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I found it for sale on the UK Amazon site for £37.50 including delivery.

Quite dear Chinese compared to ebay. But still cheap.

My comment, do you need 350A ? If not a 100A shunt could be 3.5X as accurate so logging a single LED lamp.

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Jan 19, 2014
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Wouldn't have thought the current rating of the shunt would effect accuracy. The resistance will be the same. Ours is a 200a rated shunt and is accurate to 0.1a. Often I see it registering 0.1 and then realise I've left something on :rolleyes:
 
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Two on Tour

Two on Tour

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The ones with LED displays tend to use more power. It just says "low power consumption" hmm that might be more than the solar puts in, in winter.
Same goes for all these Chinese ones, how long will they last? Personally if I'm drilling holes in my lovely new ish van I'd fit a high quality instrument :love:

https://www.nasamarine.com/product/bm-1-battery-monitor/

Iirc 6ma power usage :love:

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Lenny HB

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hilldweller

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Wouldn't have thought the current rating of the shunt would effect accuracy.

It all depends on the resolution analogue to digital converter just how much the accuracy suffers plus the maths used to do the calculations. But no matter what it is, a 100A shunt would give 3.5 times the voltage to measure so possibly 3.5 times more accuracy.
 
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yeh if i had an expensive motorhome i might go with the bm1.
think i will just go with a simple volt meter that says it has an on/off switch.
from memory 12.7v 100% good. 12.3v or .4v = 50% switch a few things off. 12.0v in desperate need of recharging.
 
Jan 19, 2014
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yeh if i had an expensive motorhome i might go with the bm1.
think i will just go with a simple volt meter that says it has an on/off switch.
from memory 12.7v 100% good. 12.3v or .4v = 50% switch a few things off. 12.0v in desperate need of recharging.
Problem with that is you have to let the battery rest for 2 hours before taking the reading. Nothing's easy is it :rolleyes:

Oh, also that method doesn't give capacity, just state of charge.
 
May 7, 2016
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A cheap digital voltmeter will tell you all you need to know about the batteries state of charge without all these setting and expense.
Voltage might tell you all you need to know but doesn’t tell me all I need to know.

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Sep 10, 2012
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yeh but it will make me feel better having a little gauge to look at even if its not telling the whole story and for the princely sum of £3.50 delivered from china i can live with that.:D
 

Lenny HB

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It all depends on the resolution analogue to digital converter just how much the accuracy suffers plus the maths used to do the calculations. But no matter what it is, a 100A shunt would give 3.5 times the voltage to measure so possibly 3.5 times more accuracy.
I do t see that surely the only difference between a 100 amp shunt and a 350 amp one is the power handling I would have thought the resistance would be the same therefore the accuracy would be the same.
 

hilldweller

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I do t see that surely the only difference between a 100 amp shunt and a 350 amp one is the power handling I would have thought the resistance would be the same therefore the accuracy would be the same.

Why would the resistance be the same ?

It depends on the designer. If he set the calculations for 350A full scale on the ADC then swaps to a 100A shunt he gets only 1/3rd of the potential resolution at the input. Whereas if the 100A shunt gives full scale he can log smaller loads.

I have this problem with my Sargent controller, I queried a silly quiescent current of 400mA but they came back and said 400mA is the max resolution so basically ignore it.
 
Jan 19, 2014
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Why would the resistance be the same ?

It depends on the designer. If he set the calculations for 350A full scale on the ADC then swaps to a 100A shunt he gets only 1/3rd of the potential resolution at the input. Whereas if the 100A shunt gives full scale he can log smaller loads.

I have this problem with my Sargent controller, I queried a silly quiescent current of 400mA but they came back and said 400mA is the max resolution so basically ignore it.

In my mind swapping to a smaller 100a shunt would make no difference until you tried to pull more than 100a through it. Then it would melt.

I see what you mean about a third of the full scale but digital meters have big autoranging scales. Well hopefully they do :D2
 
May 7, 2016
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Who says size doesn’t matter, an undersized shunt clearly leads to disappointment. :)

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Apr 27, 2016
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A shunt has the electrical resistance of a short bit of thick wire. The point is, it is known very accurately and precisely. By measuring the very small voltage drop across this accurate resistance, the current (amps) can be calculated quite accurately.

A typical shunt will measure 100 amps, and the voltage drop for 100 amps is 50 millivolts. Doing the maths, its resistance is V/I = 50mv/100A =0.0005 ohms, or 0.5 milliohms, or 500 micro-ohms. The software translates the measured 0 to 50mV to the current of 0 to 100A

A 350 amps meter could use the same display/measuring device (measuring 0 to 50 mV), but the software would display it as 0 to 350 amps. A different shunt resistance is required. The new shunt resistance would have to be V/I = 50mv/350A = 0.000143 ohms = 0.143milliohms = 143 micro-ohms.
 
Dec 30, 2017
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Just installed one of these the other day.
Bit fiddly attaching the cables to the blocks as the bolts aren't fixed and access thru the cover is a bit tight. I ended up using 2 jumper cables, 1 to the battery negative and 1 to a "busbar" to which I attached the negative wiring.
Working well so far as I can tell.
Display is very readable and works either on the usb cable supplied or over a wireless connection with external power.
Looking at your shunt it has 2 bars across it whereas mine has only one. However, stamped on the edge of 1 of the blocks it says 100A, wondering what yours says?
 
Last edited:
Dec 31, 2010
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Sunny South Shields
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Just installed one of these the other day.
Bit fiddly attaching the cables to the blocks as the bolts aren't fixed and access thru the cover is a bit tight. I ended up using 2 jumper cables, 1 to the battery negative and 1 to a "busbar" to which I attached the negative wiring.
Working well so far as I can tell.
Display is very readable and works either on the usb cable supplied or over a wireless connection with external power.
Looking at your shunt it has 2 bars across it whereas mine has only one. However, stamped on the edge of 1 of the blocks it says 100A, wondering what yours says?

Hi yeah I seen that problem with the bolts on one of the youtube videos, I might change mine to 6mm from the 8mm bolts as my battery connectors are 6mm, mine has 200A on the the side of the shunt this is the one I bought which is 100amp https://www.ebay.co.uk/itm/JUNTEK-D...e=STRK:MEBIDX:IT&_trksid=p2060353.m2749.l2649
 
Dec 30, 2017
141
163
North Devon
Funster No
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Hi yeah I seen that problem with the bolts on one of the youtube videos, I might change mine to 6mm from the 8mm bolts as my battery connectors are 6mm, mine has 200A on the the side of the shunt this is the one I bought which is 100amp https://www.ebay.co.uk/itm/JUNTEK-DC-0-01-100V-0-01-100A-Wireless-Digital-Voltage-Current-Power-Meter-C2K1/392243518738?ssPageName=STRK:MEBIDX:IT&_trksid=p2060353.m2749.l2649
Thanks for that. You did better than me I paid 27 from amazon. Well done you.

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