Strange Nasa BM1 problem

I rewired the black and white wires. This does not change anything. At the end of the new black and white wires I measured 0,3. At the beginning of the wires (on the shunt) the measurent is 0,0.
I have positioned the new wires different from the old (to avoid possible magnetic fields). Nothing changed.
We seem to be out of ideas, are we?
 
We seem to be out of ideas, are we?
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I reckon we are!

I do not understand how this 0.3 volt difference can arise unless one of the wires is carrying a significant current or there is a bad connection or resistance somewhere

The white wire probably caries very little current as it is, with the yellow wire, only measuring the volts across the shunt ( that by the way should only be 50mV max IIRC) The black wire only caries the current which the instrument takes. Only few mA if the back-lighting is not on.
 
slightly off topic I fitted a BM1 recently and athough mine works fine i do think the shunt is a bit poor by that i mean small. By the time youve got the main neg off it and the starter bat neg off it the bolt is too small for anything else. I would have gladly paid a bit more for something a bit more substantial.
 
dougg said:
slightly off topic I fitted a BM1 recently and athough mine works fine i do think the shunt is a bit poor by that i mean small. By the time youve got the main neg off it and the starter bat neg off it the bolt is too small for anything else.
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You should connect the shunt to the starter battery negative and make the starter battery negative the common ground i.e. there is no need to connect more than one cable (either end) to the shunt.
 
VicS said:
I reckon we are!

I do not understand how this 0.3 volt difference can arise unless one of the wires is carrying a significant current or there is a bad connection or resistance somewhere

The white wire probably caries very little current as it is, with the yellow wire, only measuring the volts across the shunt ( that by the way should only be 50mV max IIRC) The black wire only caries the current which the instrument takes. Only few mA if the back-lighting is not on.
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Agreed! I've given up. :(
 
dougg said:
Nice thanks.:D
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Already posted in this thread but this diagram shows the idea

scan0058.jpg
 
got a new one!

I got a new BM-1 (with a fair discount from the shop owner). I used the old wire, but the new shunt. Everything works like it should (up to now). So I suppose the problem was the display unit itself.
fyi: the new version has an orange wire that may be connected with the + of the starting battery. Also the shunt looks very different (a bit cheap actually). But at least it functions like it should.
Thanks for all you help on this topic!
 
Glad you have got it sorted and thanks for letting us know.

A faulty unit was about the only possibility left.

Please add the orange wire to my diagram. :)
 
For the benefit of anyone else still following the thread who may have problems, I have come across yet another instance where erratic behaviour of a BM-1 has been caused by very slight resistance in the main (red) power feed at the in-line fuse holder. This again caused unexplained readings when the backlight was turned on/off.

A similar internal fault (dry joint etc) could very well have been the problem all along.

Vic
 
My 3 Amps problem solved

VicMallows said:
For the benefit of anyone else still following the thread who may have problems, I have come across yet another instance where erratic behaviour of a BM-1 has been caused by very slight resistance in the main (red) power feed at the in-line fuse holder. This again caused unexplained readings when the backlight was turned on/off.

A similar internal fault (dry joint etc) could very well have been the problem all along.

Vic
Click to expand...

Dear all,
I can confirm problems due to fuse holder. I obtained readings of 3A in excess when the light was ON. Now I have upgrade fuse holder and the problem is solved.
Thanks to all.
 
nasa

hi i have just fitted a compact BM-1 have put the shunt before the neg bus bar ,reads amps ok ,i think but does not show charging when engine running shows a small discharge HELP cheers Mark
 
You must wire the shunt exactly described in the instructions.

The shunt must be between the neg bus bar and the battery terminal.
Apart from the BMI connections all other connections must be to the negative bus bar

This diagram may help. Where it says no other connections it means no other connections
scan0058.jpg

NB Orange wire to starter battery not shown
 
20110913_18.jpg
hi thanks for your replys this is where i put mine ,what do you think ,tonight when i put the land line battery charger on it read 8,0 volt charge ,but when i run the engine it reads discharge 1.3 ,i have a sterling battery to battery charger hope you can help thanks Mark
 
The wiring visible in your pic looks fine. Can you confirm that there is NOTHING else connected to the negative post of the battery that the shunt is connected to. (no links to another battery; no connection to your Sterling charger; ......nothing at all) ?

Vic
 
You guys may find this useful. This is a White Paper written about Battery Monitors and SmartGauge. It's a bit "salesy" but covers most of the points made in this thread. SmartGauge has been professionally tested by Enersys (the world's largest battery manufacturer) in their labs in Newport and they've confirmed the claims about accuracy.

Installation

Conventional battery monitors use a shunt based system that measures the net amount of current running in/out of the battery. From this they can then calculate amp hours in/out. Combined with voltage and an algorithm known as Peukert’s Exponent, they then display a calculated percentage remaining. Other features include voltage, net current in/out and on certain models, time remaining. Installation of the shunt is critical. It must be connected in series (in the negative cable) with the batteries – no other connection
may be made directly to the battery negative (often ignored by installers of other equipment, causing immediate inaccuracy of the battery monitor). The shunt must be of a large enough size to handle all current in/out of the battery (including emergency cranking current if a battery parallel switch/contactor is used). Therefore, most battery monitors are supplied with a 500A shunt (some are supplied with a small 100A shunt that can't be safely used on most marine and vehicle installations). The cabling to the shunt must be of equal size to other battery cables – again an issue for most end users as they do not have the crimping equipment required. Typically, 5 wires are run from the monitor head unit to the shunt and battery bank.

On installation, conventional monitors then need to be programmed and synchronised to the batteries (often the shunt needs further calibration, often known as ‘zeroing’). This includes inputting the battery’s theoretical capacity in amp hours, battery type and Peukert’s Exponent. The batteries then need to be fully charged (usually overnight) and the battery monitor reset.

Most battery dealers are often unaware of what Peukert’s Exponent is, let alone the values for the batteries that they sell. In this case, to determine the Peukert’s Exponent for a given battery requires a complex test and calculation to determine the actual number. Our website covers this and provides a useful tool for determining the actual Peukert’s Exponent for any lead/acid battery: http://www.smartgauge.co.uk/peukert_depth.html

These requirements for installation of a conventional battery monitor are within the capabilities of a good DIY installer. However in our experience, virtually all tech support calls are due to installation, programming and set up not being completed correctly.
Usage Battery technology and chemistry is a complex subject and misunderstood by many.
In our experience, many of the features of monitors are lost on individuals. For example, the operator of say, a CCTV vehicle does not understand the relationship between voltage and current. The training required for such operators is beyond what most organisations provide. Essentially, the key information that the user requires is exactly
the same as a fuel gauge on a car, and that is, how much capacity is remaining in the battery.

The deluge of information available actually serves to confuse even the more knowledgeable users rather than educate them. For example, the industry is rapidly moving towards using AGM battery technology over conventional wet lead/acid. An AGM battery delivers around 60% of its amp hour output at a much lower voltage than a conventional battery. We are finding that this is not only confusing the battery monitors (if not set up absolutely correctly) but also the more knowledgeable individuals whose historical experience of conventional batteries tells them that they are virtually flat at 12.4
volts.

Accuracy

Perhaps the biggest issue surrounding battery monitors is that of accuracy, not in terms of voltage or current measured, but in terms of capacity remaining and amp hours used. During a charge and recharge cycle, the battery monitor will be inaccurate by 5 or 10%. As the batteries are continually charged and discharged, this inaccuracy accumulates so that after just 3 charge/discharge cycles, the monitor’s display of amp hours/% remaining can be out by up to 30%.

To overcome the above problem, manufacturer’s have included an automatic reset function that typically resets the meter when voltage and current match a given set of parameters. There are two disadvantages associated with this. Firstly, if the batteries are being continually cycled and never reaching a fully charged parameter (certainly this is the case for the vast majority of vehicles and long distance yachtsmen), the meter won’t reset automatically. Secondly, to recharge above 80% takes a mains powered battery charger
hours (or days) to achieve – therefore many monitors reset at 85% (and then show 100%), confusing the user into thinking that the batteries are fully charged. In addition, the rest parameters must be matched to the battery type, capacity and voltage – a programming step often missed by most installers that further compounds the problem.

In a cost effective battery monitor, the above accuracy problems cannot be overcome using conventional, shunt based (amp hour counting) battery monitors.
It should be noted that in bench testing conditions, within a controlled environment, shunt based battery monitors do work very well (due to performing full cycle tests and using a mains powered battery charger). However, in the environment found on most boats and vehicles (where full charge/recha rge cycles are rarely performed), the accuracy issue will affect all shunt based meters.

SmartGauge

SmartGauge was designed to overcome the big three problems associated with conventional battery monitors. As at the time of writing it is the only battery monitor available today that utilises other methods of battery capacity testing to overcome these issues.

The actual methods of measurement of battery capacity is proprietary information but are based on advanced computer modelling of a lead/acid battery. The methods used combined with a complex algorithm ensures that all installation, usage and accuracy problems are totally defeated.

Installation

Installation of the SmartGauge monitor is simply two (or three wires). Neg/Pos1/Pos 2. Installation time is reduced from 2-3 hours down to 25 mins with SmartGauge. No specialist tools, additional large cable links or twisted pair instrument cable is required.
Programming is simple, all that is required is selection of the battery type and selection of alarm thresholds.

SmartGauge can be used on 12/24V battery banks of any capacity (regardless of the number of batteries in parallel or series).

Usage

SmartGauge provides the user with quick, clear and concise battery information, namely, battery voltage and battery capacity remaining (as a percentage %). The unit will also display the voltage only of a second battery. Typically, the main battery being monitored being the auxiliary or domestic battery bank and the voltage only battery being the engine start/chassis battery.

No training apart from informing the user when to recharge the battery (when SmartGauge displays 50% capacity remaining) is required. The unit’s low voltage/capacity alarms also warn the user of low battery capacity. Because most users (who have little or no knowledge of batteries) have little to learn about the product, it is far more likely that they will be able to effectively use the data that SmartGauge provides.

Accuracy

Because SmartGauge uses continuous and real time battery measurement techniques, and no amp hour counting as a primary method of battery capacity calculation, the unit is not affected by synchronisation issues. What’s more, the unit learns about the battery and its characteristics cycle after cycle. The Capacity (%) remaining display is constantly updated and includes battery degradation over time. Conventional monitors always display 100% remaining when a battery is fully (or near to fully) charged – even if 70% of capacity has been lost to sulfation or stratification. This is a major failing of conventional battery monitors – the % remaining figure they display is calculated on the theoretical Ah capacity of a new battery, not the actual capacity available (which is always less due to sulphation and stratification). Like every other economical (sub £1000) battery monitor, SmartGauge is accurate to a point. Due to the way batteries work, SmartGauge Capacity Remaining is accurate to within 5% during the mid point of the discharge cycle and to within 10% during mid recharge cycle. Note that this is only during the middle part of the battery charge/recharge curve. The unit achieves virtually 100% accuracy as the batteries near either being fully charged or fully flattened.

Other Points

It has been widely debated about adding further displays to SmartGauge, such as time remaining etc. However, current thinking is not to include these features as they are not accurate on conventional monitors (unless properly set up in controlled conditions) and in most cases, will confuse untrained users. The ethos of SmartGauge is to provide accurate, easy to interpret data.

Power Drain

All battery monitors have to be left running at all times. Therefore current draw is extremely important – especially if vehicles/marine craft are left for periods of time without a charging source. SmartGauge uses less than 5mA (equal to 3.7 amp hours per month) – the lowest of any other monitor currently being sold.
 
amps

20111005_8.jpg
20111005_3.jpg
]hi Vic took these pic showing two of the 3 leisure batteries the starter battery is connected to the neg side also ,the other pic shows the charger set up one of the negs in the pic goes to the inverter
 
foden01 said:
these pic showing two of the 3 leisure batteries the starter battery is connected to the neg side also ,the other pic shows the charger set up one of the negs in the pic goes to the inverter
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We'll it seems you DO have other connection(s) to the domestic bank negative, apart from the shunt.

As we have all said numerous times, the negative side of the domestic battery bank must ONLY be connected to the shunt ..... not to the starter battery negative ..... not to anything else. (as per VicS diagrams).

ALL other connections should be to the other side of the shunt (or to a something connected to the other side of the shunt, such as a busbar or the engine block).

Vic
 
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