Battery monitor

[braehouse]

Have a look at this

I have had one of these for 2 years now and find it a great bit of kit.

http://www.power-store.com/view-item.asp?itemid=1693


Chris

 

[GrahamM376]

NASA BM1 does all these.

I've fitted two BM1s, one to each house bank. Don't monitor the engine battery. Very accurate on volts and amps but, like some others, level of charge indication is a bit tongue in cheek.

 

[noelex]

Very accurate on volts and amps but, like some others, level of charge indication is a bit tongue in cheek.

The charge level is reset when the batteries are fully charged. For the level to be accurate after more than a few days you need a battery monitor that has an adjustable charge factor compensation. ( to allow for the fact that batteries have different efficiencies if you put 100AHr in most batteries will allow a about 80 to 95 AHrs to be withdrawn and maintain the same SOC) Unfortunately not many monitors allow this efficiency factor to be adjusted and some cheap ones assume 100% efficiency so the SOC indicator becomes inaccurate quickly
You can still get a good indication of the state of charge even if the SOC display is inaccurate, by looking at the battery voltage combined with the charge or discharge current.

 

[cmedsailor]

I've fitted two BM1s, one to each house bank. Don't monitor the engine battery. .

You can check (only) voltage of the engine battery, unless you have the older units.

 

[Barry Jones]

I use Smartgauge because battery monitors that measure current charged and discharged over time using a shunt, will lose synchronisation with the state of charge after a while.
This is due to a number of factors such as specific battery charge and discharge characteristics, exact Peukerts numbers for the battery in question, battery ageing etc.

The only way to re-align these is to fully charge the battery and then reset the counter, which is a pain.

My understanding is that the Smartgauge only measures voltage trends against time and uses some clever algorithms, so is adaptive.

 

[noelex]

My understanding is that the Smartgauge only measures voltage trends against time and uses some clever algorithms, so is adaptive.

Yes it only measures voltage. Its impossible to accurately measure the SOC with this single parameter.

 

[Barry Jones]

I and a lot of satisfied Smartgauge customers disagree.

http://www.smartgauge.co.uk/why_sga.html

Yes it only measures voltage. Its impossible to accurately measure the SOC with this single parameter.

 

[halcyon]

Yes it only measures voltage. Its impossible to accurately measure the SOC with this single parameter.

Agree, would love someone to come on and prove how it can.

There are two many variables in battery voltages reading to SOC, a change of 20F will give a voltage swing equal to 6% battery capacity, 12.7 volt may be a nominal 100%, but a new battery can be over 13 volt. Then you add battery production tolerence, air pressure, how the battery is charged, how it is used or abused, is a solar panel or wind gen fitted.

Brian

 

[Porthandbuoy]

Half hour might not be enough to tell much about the state of charge from voltage.. http://www.pbase.com/mainecruising/battery_state_of_charge

True, but if it reads 11.something I know the battery is significantly discharged, and when it reaches 14.4V with the engine running I know it is charged as much as it can take. A knackered battery will still reach 14.4V, it'll just deliver fewer amphours than when it was new. (Pedants note, I'm not talking shorted or open circuit cells, just a battery past it's best).

No battery lasts forever, they all have a limited number of charge/discharge cycles. How many depends on rate and depth of discharge, how long left discharged, and how 'aggressive' the charge. How tolerant a battery is to these factors depends to a large extent on its construction.

 

[Trundlebug]

The great thing about the BM1 is that it will count the number of Ah's you have used since last charged, which gives a very effective indication of the remaining charge.

If you know the total battery capacity, have an idea of their general condition and how fast they have been discharged. Which barring the capacity are all measured and indicated by the BM1 so you should have

It will also tell you how many Ah's have been charged into the batteries, another useful indication.

Good value compared to some other instruments too.

 

[noelex]

I and a lot of satisfied Smartgauge customers disagree.

http://www.smartgauge.co.uk/why_sga.html

I have often wondered how they know the soc meter on the Smartguage is reading correctly ?

 

[prv]

Agree, would love someone to come on and prove how it can.

Sadly I don't exactly how it works, and I can quite understand people's scepticism towards it. It's only right to be wary of anything sold with a message of "just trust us, it does work", and it would be great if Mr Gibson were to publish exactly how it functions and remove the mystery. Sadly I suspect he regards the details as a trade secret and keeps them to himself.

For what it's worth, it seems to work for me. I agree you probably shouldn't take that as any kind of proof.

The one thing I will say in response to "it only measures voltage. Its impossible to accurately measure the SOC with this single parameter" is a reminder that it's not working off a single instantaneous reading of voltage. Instead it tracks the voltage profile over time as the battery charges and discharges - according to the Merlin boss (who may or may not know what he's talking about, of course) it looks more at the shape of the curve than at the absolute values.

Pete

 

[Barry Jones]

Despite peoples cynicism about Smartgauge, which of course, you are quite at liberty to have, it does work.

I wonder how many people with Amp-Counter monitors have actually set them up properly at installation and when did you last reset them to synchronise them with the battery bank ??

 

[Barry Jones]

Because some people know how to test batteries the manual way - and the numbers stack up. Also, I have been able to compare the two technologies side by side.

I have often wondered how they know the soc meter on the Smartguage is reading correctly ?

 

[noelex]

I wonder how many people with Amp-Counter monitors have actually set them up properly at installation and when did you last reset them to synchronise them with the battery bank ??

Synchronization is automatic when the batteries have been full charged.

I do agree a lot are not set up right and on some monitors, there is no adjustment possible for important parameters that will effect the accuracy of the SOC display.

 

[VicMallows]

Synchronization is automatic when the batteries have been full charged.

Are you talking about the % charge indication? Certainly the cumulative AH counter does not ' automatically synchronise' on a BM-1 .... and I cannot think of any way it could or should?.

I simply reset mine whenever I feel confident the batteries are fully charged (PV charging at 14.2v for several days) .... and also after leaving the boat for some weeks with batteries fully isolated. The inevitable inaccuracy means that there is always a totally meaningless AHr indication after such a time. (in fact better to disconnect the BM-1 and save the small power drain).

Vic

 

[Barry Jones]

I believe the NASA one has to be manually synchronised.

ETA sorry cross posted with Vic.

I don't believe this model allows you to set the Peukerts factor either ?

 

[Conachair]

Are you talking about the % charge indication? Certainly the cumulative AH counter does not ' automatically synchronise' on a BM-1 .... and I cannot think of any way it could or should?.

I simply reset mine whenever I feel confident the batteries are fully charged (PV charging at 14.2v for several days) .... and also after leaving the boat for some weeks with batteries fully isolated. The inevitable inaccuracy means that there is always a totally meaningless AHr indication after such a time. (in fact better to disconnect the BM-1 and save the small power drain).

Vic

Mine resets automatically to 100% with user definable parameters.

http://www.bepmarine.com/home-mainmenu-8/product-360/600-dcm-contour-matrix-dc-monitor

From memory if charge rate is continually under, say, 0.5a for 10 minutes the unit will reset to 100%. Also has user definable Peukert's constant. Otherwise it will start to drift. Seems to stay accurate when checked with hydrometer readings.

 

[VicMallows]

Also, I have been able to compare the two technologies side by side.

Now that is something I would be very interested to do!. If anyone wants to lend me a SmartGauge to conduct a proper technical comparison under real life conditions and over a worthwhile period I will be happy to do so

Vic

 

[Barry Jones]

No problem, but it needs special delivery and that costs £150.

Now that is something I would be very interested to do!. If anyone wants to lend me a SmartGauge to conduct a proper technical comparison under real life conditions and over a worthwhile period I will be happy to do so

Vic