Victron bmv600 confusion

[monte]

Just a quick note to those using battery monitors that will be obvious to some more experienced sailors but oblivious to others (like myself)
When I installed my battery monitor I expected the percentage to show the actual percentage of battery remaining, and decided this is the simplest way for me to monitor the state of my batteries.
However, as the percentage is a calculated guesstimate of amps used/amps charged it can become out by up to 20% over time. It is in fact fairly close within a few days after the batteries are fully charged but after a couple of weeks of not plugging in it could be well out because amps out are actually higher than those read by the monitor (due to Peukerts law ). Sure the monitor applies an adjustable value for this, but its not always accurate. So after a couple of weeks of saing and anchoring, relying on solar and wind to charge the batteries, the monitor might say batteries are at 65%, but, the voltage is at 12.2V. The voltage indicates the batteries are actually at 50%. This reading will be most accurate after the batteries have rested for a while (probably first thing in the morning)

These are approximate voltages/% of charge
12v - 40%
12.2v-50%
12.4v-65%
12.6v-80%
12.8v-100%

Hopefully this will help someone (and their batteries) as it has taken me a while to figure it out!

The monitor is a good piece of equipment, it will tell the amps out, and amps in, which can be really useful, and the % state of charge is fine to use if you fully charge regularly, just don't rely on it if its weeks between fully charging your batteries.

Corrections or clarifications are welcome, I just wanted to state my views in case it helps others.
Cheers
Monte

[Canibul]

I installed the Victron. The installation was easy. What I use it for is to check the battery voltage, and I look at amps in vs amps out. I had nothing before, so this is a step up.

[T1 Terry]

When it comes to using one of these BMV's with lead acid batteries, I think if the Peukert factor is exaggerated along with a less than optimal charging efficiency and 10% reduced actual battery capacity, the Victron BMV would run fairly close to the mark. The settings can be fine tuned if the owners sees the figures are out of wack, like 98%SOC with a rested terminal voltage of 12.6v or lower, a poorer Peukert's factor and poorer charge efficiency need selecting, if the terminal voltage is 14.4v or higher yet the SOC percentage is still around 50%, you may need to lighten up a bit of the charge efficiency first, then the Peukert factor second if the charge efficiency is already at 85%.
If the figures are staying close around the 70% plus figure yet drift a long way out if dropped to the 50% SOC range, readjust the battery capacity down to 10% less and try again.
I think the biggest problem is people lieing to themselves about the efficiency and condition of their battery pack, the monitor is telling you the facts and many people can't accept that they have been duped into believing their lead acid batteries are a lot better than they really are.

T1 Terry

[Dockhead]

Originally Posted by Ex-Calif

As I get ready to actually open the wallet I am getting serious about reading. Mainesails articles and your advice and others basically point out that one absolutely has to understand

- how the calibration works and the data it needs
- You batteries deteriorate and calibration needs to be redone
- If you are not interactive and active eventually the soh will be useless

To be honest - when there was nothing else a/h counting could be made to work well but I think I am going to go with the Smartgauge. Over the life of the gauge the ~$100 bucks difference is not a big deal I think.

I guess the average person "guesses" at some of this stuff and that to me is a big downside.

I think (based on your testing) I am going to go with the SmartGauge - It appears to be the next gen.

I understand the Smartgauge does not have a a/h counter or amp gauge - I understand why but it is a disappointment.

I have been Goggling and searching for an amp gauge but have not found anything that is suitable or if suitable really expensive.

Any recommendation for a digital ammeter or preferably ammeter/voltmeter combo?

As always thanks for your advice around here!

You want a DC clamp meter in your tool bag anyway. Sinometer makes a Cheap but good enough for our purposes one sold under various stencil brands (including Radio Shack) for less than $100.

I have been running an electrical system an order of magnitude more complex than yours for a couple of years now with nothing but the voltage meter built into the chart plotter, and a Radio Shack clamp meter, with very good results. No need to terribly overthink it.

[Ex-Calif]

Originally Posted by Dockhead

You want a DC clamp meter in your tool bag anyway. Sinometer makes a Cheap but good enough for our purposes one sold under various stencil brands (including Radio Shack) for less than $100.

Thanks Dock.

Getting real close to placing the order. Appreciate the advice.

[sailorboy1]

The Victron BM works just fine once you get it programmed correctly. Do a search on my past threads and you will find the topic has been covered pretty deep.

[Dockhead]

Originally Posted by Ex-Calif

Thanks Dock.

Getting real close to placing the order. Appreciate the advice.

Cheers. The serious electricians will sneer at this device compared to $800 Flukes, say, but I have some even fairly complex things with the Sinometer multimeters and they work well. For volts and amps they are reasonably accurate, and measuring individual circuits will give you much better information than a single current reading for the whole boat.

By the way, I think MaineSail has one of these in his collection of multimeters.

[Dockhead]

Originally Posted by T1 Terry

When it comes to using one of these BMV's with lead acid batteries, I think if the Peukert factor is exaggerated along with a less than optimal charging efficiency and 10% reduced actual battery capacity, the Victron BMV would run fairly close to the mark. The settings can be fine tuned if the owners sees the figures are out of wack, like 98%SOC with a rested terminal voltage of 12.6v or lower, a poorer Peukert's factor and poorer charge efficiency need selecting, if the terminal voltage is 14.4v or higher yet the SOC percentage is still around 50%, you may need to lighten up a bit of the charge efficiency first, then the Peukert factor second if the charge efficiency is already at 85%.
If the figures are staying close around the 70% plus figure yet drift a long way out if dropped to the 50% SOC range, readjust the battery capacity down to 10% less and try again.
I think the biggest problem is people lieing to themselves about the efficiency and condition of their battery pack, the monitor is telling you the facts and many people can't accept that they have been duped into believing their lead acid batteries are a lot better than they really are.

T1 Terry

Yes, this is the usual error with amp-counting methods of evaluating SOC. All the errors lead to overestimation of SOC. This is really bad, because it means you will be running your batteries down too far in blissful ignorance that your batteries are really flatter than you think.

Another plus of the crude voltage method I use is that all errors work the opposite way -- to underestimating, rather than overestimating SOC. So it means if you are watching voltage, you don't have to worry about having perfect conditions for your test -- you don't have to unclamp the batteries and wait for four hours. As long as you have a load on which is a small enough fraction of C that it doesn't grossly distort the reading, and haven't had any heavy loads for some time. You will be off a little due to the loads you have, but in the conservative direction. So you can run your batteries down confidently to 24.2V (or 12.1V) under light loads and you can be pretty sure that you haven't run them down below 50%.

The more I have lived with this system, the more convinced I have become that you really don't need more precision than this. More precision is going to be false precision anyway, unless you have gone through all the rigamarole described in posts of others to get the amp-counting meter precisely calibrated. And if you haven't gotten it precisely calibrated, is it really more precise than a simple voltage method? Terry's simplified calibration method has you fudging the battery capacity by 10% C at a time -- surely any voltage method is going to get you closer than immediately and effortlessly. Considering that the errors of amp-counting methods work against you, is there really any point to this at all? I think not -- the more I think about it.

But one caveat, as I said -- this works better with larger banks than with smaller ones. If your battery bank is so small that you can't practically get voltage-bending loads off it, then my method won't really work.

[gamayun]

I'm commenting on this post because I'm planning to buy one of these monitors, still new in the box, for half price from someone who decided to go a different route. I want to be able to find this info again when I get around to installing it.

[Dod42]

Having sorted all the wiring and getting everything to go via the shunt it all now looks much better and realistic. Next step this weekend is to unplug and run at the dock as if we where at anchor and see what our real consumption is like.

The meter did make me wonder about the Victron Charger/Inverter that was installed as well, so had the local agent down to look at the setup. In the end it was setup quite well from the factory, and some of the information will help me setup my new MPPT solar controller properly. I have also purchased the data pack for the BMV600 that allows for importing historical data from the monitor into my PC so I can look at usage over time. Once I have a bit of data to give meaning full stats I will post the graph.

[monte]

Originally Posted by gamayun

I'm commenting on this post because I'm planning to buy one of these monitors, still new in the box, for half price from someone who decided to go a different route. I want to be able to find this info again when I get around to installing it.

Installing A Battery Monitor Photo Gallery by Compass Marine How To at pbase.com

Thanks to Maine Sail

[Dockhead]

Originally Posted by monte

The monitor is a good piece of equipment, it will tell the amps out, and amps in, which can be really useful, and the % state of charge is fine to use if you fully charge regularly, just don't rely on it if its weeks between fully charging your batteries.

Yes, this is certainly true -- if an amp-counting battery monitor doesn't get a reset to 100%, it will soon lose any clue about the battery state of charge. As you correctly said -- this is not a problem if you are regularly on shore power and getting a full charge, but is a big problem if you are (like me) on a mooring without shore power, or off the grid for extended periods.

But this is not the only problem with amp-counting battery monitors -- they also need to know the real practical capacity of the batteries. There are two obstacles to this: (a) the real practical capacity will not be the same as what is written on the label; and (b) the real practical capacity is changing constantly as the batteries age.

Besides this, the monitor needs to be know the real, practical Peukert's Constant for your battery, about which likewise with capacity -- it's not necessarily the same as what is on the spec sheet.

All of this adds up to quite a mountain of obstacles to getting an accurate SOC reading out of an amp-counting battery monitor, without going to a heap of a lot of trouble.

[Ex-Calif]

Originally Posted by Dockhead

Yes, this is certainly true -- if an amp-counting battery monitor doesn't get a reset to 100%, it will soon lose any clue about the battery state of charge. As you correctly said -- this is not a problem if you are regularly on shore power and getting a full charge, but is a big problem if you are (like me) on a mooring without shore power, or off the grid for extended periods.

I think most agree with the practical limitations of accurately assessing SOC with an amp counter but I find amps in/out/cum in/cum out useful along with voltage - especially if downloadable.

I've been Googling but have not found a (cheap) gauge that simply does that. I haven't looked everywhere but certainly a lot of the major boat and soloar suppliers.

I am reconciled to buying both BMV and Smartgauge and ignoring the BMV SOC. IN the big scheme of things it's $160 over the cost of the SmartGauge.

[sailorboy1]

Originally Posted by Ex-Calif

I am reconciled to buying both BMV and Smartgauge and ignoring the BMV SOC. IN the big scheme of things it's $160 over the cost of the SmartGauge.

Why? All the problems over the years I've read of (including mine) where the BMV reset too early are due to not setting the voltage high enough to ensure that the battery had to be in absorption when the low amp setpoint is reached.

[Ex-Calif]

Originally Posted by sailorboy1

Why? All the problems over the years I've read of (including mine) where the BMV reset too early are due to not setting the voltage high enough to ensure that the battery had to be in absorption when the low amp setpoint is reached.

Manual resets...