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NASA BM2 Settings.

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My Nasa BM2 arrived lunchtime so just spent just over an hour to wire it in.

On the setup it asked what your battery capacity was, so thought from memory it was 242ah as a pair of Trojan T105's, is that correct?

Also asked the average battery temperature in O C. I left it at 20 but what would you suggest? Batteries are on top of the swim next to engine in box/ cupboard In a modern trad.

Turned off the charger for setup, and let it do its own thing with a fridge running. It adjusted it's settings and then I put the charger back on, it went to float in minutes.

Decided to fit the monitor at the end of my bed so I can see it easily! Very easy to see what's happening. Does it account for sulphated batteries?

Many thanks. James:)

 

Monitor1.jpg

Monitor2.jpg

Edited by canals are us?

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End of the bed location is good. The BM in BM2 stands for Bonk Meter but they are too polite to tell you. The time button when pressed will give you a rating of how good you were (but as a polite display of course).

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7 minutes ago, canals are us? said:

On the setup it asked what your battery capacity was, so thought from memory it was 242ah as a pair of Trojan T105's, is that correct?

Will depend on what capacity has been lost since new.

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2 minutes ago, system 4-50 said:

End of the bed location is good. The BM in BM2 stands for Bonk Meter but they are too polite to tell you. The time button when pressed will give you a rating of how good you were (but as a polite display of course).

Thank god it hasn't got a built in camera!:D

James.

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New T105s are 225AH, so 2 in series is still 225AH! (well to be pedantic, they are down on capacity until they have had 50-100 cycles but you are probably past that stage.) Not too sure what it would use the temperature for, but anyway it will depend on where the batteries are located. 20C is a bit high for a year-round average in the UK, perhaps 15 would be closer. Unless they are in an engine bay frequently run, in which case they are going to be hotter on average.

I have never owned a NASA monitor but as I understand it, they have a touch of the "smartgauges" about them during discharge. In other words, there is some sort of algorithm that doesn't just look at charge taken out to calculate the SoC, it also looks at voltage. However I am told it is very inaccurate and best not to pay much attention to it. That's what I've heard anyway. For recharge, it just counts the AH back in again. So it might give you some idea about sulphation but the best way to check for that is to fully charge the batteries and then check their specific gravity.

Edited by nicknorman

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1 minute ago, rusty69 said:

Will depend on what capacity has been lost since new.

Is there a way to test? Not worth it really as need more batteries anyway due to more capacity needed for washing machine. Going to get 4x 110ah.

James:)

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1 minute ago, canals are us? said:

Is there a way to test? Not worth it really as need more batteries anyway due to more capacity needed for washing machine. Going to get 4x 110ah.

James:)

Yeah, fit a smartgauge!:)

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3 minutes ago, canals are us? said:

Is there a way to test? Not worth it really as need more batteries anyway due to more capacity needed for washing machine. Going to get 4x 110ah.

James:)

The best way to test is to fully charge the batteries. (Probably a good idea to check the sg at that time, as capacity lost to sulphation may be recoverable). Then discharge the batteries until they are at perhaps 50% SoC by your estimation. Let them rest for an hour with zero load. Then compare the AH taken out according to the NASA, with the SoC calculated by looking at the rested no-load voltage. This will give you a fairly good idea of how much capacity is left.

Edited by nicknorman
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2 minutes ago, nicknorman said:

New T105s are 225AH, so 2 in series is still 225AH! (well to be pedantic, they are down on capacity until they have had 50-100 cycles but you are probably past that stage.) Not too sure what it would use the temperature for, but anyway it will depend on where the batteries are located. 20C is a bit high for a year-round average in the UK, perhaps 15 would be closer. Unless they are in an engine bay frequently run, in which case they are going to be hotter on average.

I have never owned a NASA monitor but as I understand it, they have a touch of the "smartgauges" about them during discharge. In other words, there is some sort of algorithm that doesn't just look at charge taken out to calculate the SoC. However I am told it is very inaccurate and best not to pay much attention to it. That's what I've heard anyway. For recharge, it just counts the AH back in again. So it might give you some idea about sulphation but the best way to check for that is to fully charge the batteries and then check their specific gravity.

I'm going to bin them in a month or so and buy 4 new batteries of 110ah each. This way I'll know the health of them. It probably wont be Trojan as just too expensive at £560 for 4. What is a cycle?

James:)

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6 minutes ago, nicknorman said:

The best way to test is to fully charge the batteries. (Probably a good idea to check the sg at that time, as capacity lost to sulphation may be recoverable). Then discharge the batteries until they are at perhaps 50% SoC by your estimation. Let them rest for an hour with zero load. Then compare the AH taken out according to the NASA, with the SoC calculated by looking at the rested no-load voltage. This will give you a fairly good idea of how much capacity is left.

I'll look for a specific gravity tester for the next set of batteries. I have saved your reply for next time. The temp only goes up and down in 10 degree increments.

Thanks. James:)

Edited by canals are us?

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20 minutes ago, system 4-50 said:

End of the bed location is good. The BM in BM2 stands for Bonk Meter but they are too polite to tell you. The time button when pressed will give you a rating of how good you were (but as a polite display of course).

My missus said our one must be broke cos it kept getting stuck on 85%

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24 minutes ago, nicknorman said:

I have never owned a NASA monitor but as I understand it, they have a touch of the "smartgauges" about them during discharge. In other words, there is some sort of algorithm that doesn't just look at charge taken out to calculate the SoC, it also looks at voltage. However I am told it is very inaccurate and best not to pay much attention to it. That's what I've heard anyway. For recharge, it just counts the AH back in again. So it might give you some idea about sulphation but the best way to check for that is to fully charge the batteries and then check their specific gravity.

3

As far as I have been able to ascertain, from watching mine in great detail and from talking to the manufacturers, they calculate the SoC during discharge (or at rest) solely from the voltage measurement, but making an allowance for the fact that the voltage will be slightly less when significant current is being taken from the batteries. Then they calculate the SoC during charge solely from the number of amp-hours that have been put in from that previously-calculated figure, relating to the number of amp-hours that you have set up. Thus, for example, if the voltage has dropped during discharge to such a level that the gauge has calculated 60% SoC, and you have set it up for a capacity of 200 Ah, then it reckons that you will need to put in 40% of 200 Ah to reach 100% so when it measures that you have put in 80 Ah it will now be showing 100%. The results are reasonably accurate once you understand how it is deriving them

23 minutes ago, canals are us? said:

Is there a way to test? Not worth it really as need more batteries anyway due to more capacity needed for washing machine. Going to get 4x 110ah.

James:)

Yes you can very accurately measure the capacity of your batteries, effectively by reversing the above process. Discharge them by a reasonable percentage - to say 80% or less - then start your engine. Keep your engine running until the charge current has fallen to a very low value (maybe just a couple of amps) and has remained that way for at least half an hour; you can now be confident that your batteries are close to 100%, despite the figure shown on the BM2. Now still with the engine running (stopping for a moment will invalidate the whole test) enter the Setup mode and try setting a different value of the capacity; exit the Setup mode and the meter will show a different SoC. Keep trying different values of capacity until the BM2 shows 100%, and you then have a readout of your actual capacity. After the first time you will see which direction to change it and guess by how much, it takes only a few seconds.

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39 minutes ago, canals are us? said:

I'm going to bin them in a month or so and buy 4 new batteries of 110ah each. This way I'll know the health of them. It probably wont be Trojan as just too expensive at £560 for 4. What is a cycle?

James:)

A cycle is discharging the battery and then recharging it again. Discharging by exactly how much, is debatable. But a significant amount say down to 75% SoC  or less. My Mastershunt counts battery cycles but it considers a cycle to be a complete discharge to 0% SoC, so it counts 2 cycles down to 50% as one full cycle.

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40 minutes ago, canals are us? said:

Is there a way to test? Not worth it really as need more batteries anyway due to more capacity needed for washing machine. Going to get 4x 110ah.

James:)

You do also intend to be running the engine with a big alternator or a travel power (or similar) whilst the washer is running, right?  Only if you're gonna run a proper domestic washing machine, (i.e. one which heats the water) off your batteries, my guess is that you're gonna go through quite a few of them!

Is it an undemanding washing machine in terms of juice?  I ask because I think the BM2 uses a 200a shunt, so I'm not sure whether that will be happy with the average domestic machine on load either. 

Not trying to teach you to such eggs James, just to make sure you don't run into problems after all the expense! :)

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36 minutes ago, Keeping Up said:

Now still with the engine running (stopping for a moment will invalidate the whole test) enter the Setup mode and try setting a different value of the capacity; exit the Setup mode and the meter will show a different SoC. Keep trying different values of capacity until the BM2 shows 100%, and you then have a readout of your actual capacity...

How does the BM2 know the charge efficiency of the battery bank during this exercise?

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41 minutes ago, Keeping Up said:

they calculate the SoC during charge solely from the number of amp-hours that have been put in from that previously-calculated figure, relating to the number of amp-hours that you have set up. Thus, for example, if the voltage has dropped during discharge to such a level that the gauge has calculated 60% SoC, and you have set it up for a capacity of 200 Ah, then it reckons that you will need to put in 40% of 200 Ah to reach 100%

It will then have got it wrong because the above scenario makes no allowance for charge efficiency. 

If you take 200Ah from a bank and then put 200Ah into that bank it will be charged to somewhere around (very roughly, and it depends on the battery and the charging voltage) 80-90%

Edited by WotEver

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3 minutes ago, WotEver said:

How does the BM2 know the charge efficiency of the battery bank during this exercise?

It doesn't. As far as I can tell it assumes it to be 100%. Of course, the error will not be cumulative because it effectively resets itself every cycle

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2 minutes ago, WotEver said:

It will then have got it wrong because the above scenario makes no allowance for charge efficiency. 

If you take 200Ah from a bank and then put 200Ah into that bank it will be charged to somewhere around (very roughly, and it depends on the battery and the charging voltage) 80-90%

Slightly pessimistic, our calculated CEF is around 94%.

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4 minutes ago, nicknorman said:

Slightly pessimistic, our calculated CEF is around 94%.

However as I said, depends on the batteries and the charging voltage. El cheapos with 14.4V will probably be closer to 80%. Whatever the figure, it ain’t gonna be 100%. 

Edited by WotEver
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32 minutes ago, Sea Dog said:

You do also intend to be running the engine with a big alternator or a travel power (or similar) whilst the washer is running, right?  Only if you're gonna run a proper domestic washing machine, (i.e. one which heats the water) off your batteries, my guess is that you're gonna go through quite a few of them!

Is it an undemanding washing machine in terms of juice?  I ask because I think the BM2 uses a 200a shunt, so I'm not sure whether that will be happy with the average domestic machine on load either. 

Not trying to teach you to such eggs James, just to make sure you don't run into problems after all the expense! :)

My washer/dryer has a hot and cold fill and I only ever use the 30 minute 30o quick wash, so hopefully  use much less electricity. I am paralleling the alternators with an VSR which are 70a and 50a. I'm hoping it will cope fine.

Mainly doing all the electrical modifications/upgrades as planning to go out of the Marina around May for a month or too. Hoping the 380 watts of solar will help top the batteries up too.

James:cheers:

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I use a BM2 but only read the voltage and current to get a view of the batteries, when charging I like to see charging amps drop to a fairly small value and when I get up in the morning I like to see the voltage above 12.4 with no load. I don't tend to look at the amps in/out or the SOC.

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45 minutes ago, nicknorman said:

A cycle is discharging the battery and then recharging it again. Discharging by exactly how much, is debatable. But a significant amount say down to 75% SoC  or less. My Mastershunt counts battery cycles but it considers a cycle to be a complete discharge to 0% SoC, so it counts 2 cycles down to 50% as one full cycle.

Thanks for the info:)

I have no idea how many cycles they have done in the 3.5 years as virtually always been on a mains battery charger and the last 2 years 380 watts of solar.

Even if the 2 do turn out ok, it's probably sensible to just buy 4 new.

James:) 

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29 minutes ago, WotEver said:

It will then have got it wrong because the above scenario makes no allowance for charge efficiency. 

If you take 200Ah from a bank and then put 200Ah into that bank it will be charged to somewhere around (very roughly, and it depends on the battery and the charging voltage) 80-90%

Thinking about it, the setup method I described will actually correct for an unknown charge efficiency, albeit while displaying a slightly optimistic value of the capacity during the setup process, thus actually giving a reasonably accurate SoC readout while in use.

Having said that, I also use mine primarily as a means of indicating voltage and current, regarding the SoC and Ah figures merely as indicators of interest (and a guide to when my batteries are getting old)

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23 minutes ago, canals are us? said:

Thanks for the info:)

I have no idea how many cycles they have done in the 3.5 years as virtually always been on a mains battery charger and the last 2 years 380 watts of solar.

Even if the 2 do turn out ok, it's probably sensible to just buy 4 new.

James:) 

It may well be, based on that usage, that the Trojans are virtually as good as new. In which case no, it doesn’t make sense to replace them :)

You need to measure their capacity first, then you’ll know. 

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2 minutes ago, WotEver said:

It may well be, based on that usage, that the Trojans are virtually as good as new. In which case no, it doesn’t make sense to replace them :)

You need to measure their capacity first, then you’ll know. 

Will do in the next few weeks. Busy working from Monday. Any recommendations as to which Specific gravity tester to buy? At least if they are ok capacity wise would I be ok to buy 2 new only and mix with the other older 2 Trojans?

Thanks. James:cheers:

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