Wanting to install a battery monitor in our Hunter 38 and need some advice on two topics. We have two battery banks in the boat (start and house). First question - any reason to monitor the starting battery? From my limited electrical knowledge, it seems unneeded as the bank we're really concerned about is the house bank - start bank takes a minimal hit during start, then fully charges on the way out. With that said, seems as though we would only need a one bank monitor - I'm sure I missed something with that logic though! Second question is what experience have people had with monitors - goods and bads and recommendations for a monitor. We're not looking for the Taj Majal of monitors - only something that will show volts and amp draw. Thanks
Battery Monitor
- Thread starter JeffThompson
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From a "battery monitor" perspective, no...
Monitors are only as good as how you program and use them. Improper programming leads to counting errors. The shunt wiring is another area people have trouble with. It is easy but people still do mess it up.... The Victron BMV-600 is the best value going and also the easiest to install.
Installing A Battery Monitor
We recently installed the Victron on the house bank on our boat and are very pleased with it. Easy to install and setup.
Bob
Bob
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And it (the 600) also measures the start bank voltage. Maine Sail wrote a whole article about installing one on the Featured Contributors section.
This one: http://forums.catalina.sailboatowners.com/showthread.php?t=125606
This one: http://forums.catalina.sailboatowners.com/showthread.php?t=125606
The 600 measures house bank only. The 602 version measures voltage only on a second bank.
I have NASA Marine BM-1 monitor installed for last two years. I cannot really think of any negative aspects of this unit, perhaps other than fact it does stay on all the time. It's power draw is so low, that it would take over a year to discharge battery, so this is rather negligible. On the positive side of features:
- shows current discharge rate and time to complete discharge of a battery
- shows current charge rates and time until battery is fully charged
- not difficult to install
- comes with shunt and 5 metres installation cable
- weather proof, can be installed outside
- weather cover included
- very good build quality
- visually appealing and goes well with other gauges
- can be used with two batteries
Personally, I give it 5 out of 5 points and consider good investment.
- shows current discharge rate and time to complete discharge of a battery
- shows current charge rates and time until battery is fully charged
- not difficult to install
- comes with shunt and 5 metres installation cable
- weather proof, can be installed outside
- weather cover included
- very good build quality
- visually appealing and goes well with other gauges
- can be used with two batteries
Personally, I give it 5 out of 5 points and consider good investment.
Maine, Dave, Bob, Stu and Bosman - thanks for the advice and the websites. I hope that my instillation goes as smoothly as Bob indicated!
These can be a good value but they lack critical programing features. They also only go to a 600Ah bank and have only a 100A shunt. Competitors such as Xantrex & Victron allow banks in excess of 1000Ah and come standard with 500A rated shunts. For small boats with small banks and light loads, eg: no windlass, large inverters, electric winches etc. they can work well. Most winches, windlasses, inverters can pull more than 100AI have NASA Marine BM-1 monitor installed for last two years. I cannot really think of any negative aspects of this unit, perhaps other than fact it does stay on all the time. It's power draw is so low, that it would take over a year to discharge battery, so this is rather negligible. On the positive side of features:
- shows current discharge rate and time to complete discharge of a battery
- shows current charge rates and time until battery is fully charged
- not difficult to install
- comes with shunt and 5 metres installation cable
- weather proof, can be installed outside
- weather cover included
- very good build quality
- visually appealing and goes well with other gauges
- can be used with two batteries
Personally, I give it 5 out of 5 points and consider good investment.
The main point with these monitors is that NASA has pre-chosen your batteries Peukert value for you. If you get lucky, and hit this pre-picked value, then it can work pretty well as a battery monitor and be pretty accurate. If you are not lucky, and your banks Peukert is different from what NASA has chosen, then the monitor can rack up some counting errors.
Here's an example of a bank I installed just yesterday and one I installed not long ago.
Bank 1
2 Trojan L16's
390 Ah's
20 Hour Rated Load = 19.5A
Peukert = 1.49
Bank 2
4 Odyssey PC2150's
400 Ah's
20 Hour Rated Load = 20A
Peukert = 1.11
Now apply an average load of 5A to each bank
Bank 1 Peukert Corrected Load = 2.57A
Bank 2 Peukert Corrected Load = 4.29A
If you drew the banks to dead at the 5A load:
Bank 1 Peukert Corrected Ah Capacity = 760 Ah's
Bank 2 Peukert Corrected Ah Capacity = 466 Ah's
We can clearly see from these banks, installed into real boats, that a one size fits all Peukert does not work well for all banks.
That said even with a monitor that has a Peukert adjustment I find many set them up improperly by not changing the value to reflect their batteries.
Maine, how do you find out the Peukert Factor for your batteries, I have 4 Deka 105 Ah, AGMs, I don't see this factor indicated on their spec sheets. Will this change as the batteries age ?
thanks, Bob
One has to keep in mind the Peukert Factor is not a static number and will change over the life of the battery. This should make sense as we all know batteries will become less efficient with age.
Capt. Wayne Canning, AMS
www.projectboatzen.com
Capt. Wayne Canning, AMS
www.projectboatzen.com
So, quick quiz, what does this mean to the battery monitor? What do you do to the Peukert setting as the batteries age..?
I tried to keep this in mind once but my mind wanted to know what to do with the information it was keeping.
I could never figure out how to use an ever changing Peukert exponent. Once I obtained a battery monitor I could not tell the monitor how it needs to behave so as to account for the change either.
Can someone explain how we calculate the rate of change, quantify the amount of change, and if we can do those things then how does anyone get any sort of practical use from this exercise?
Charles
I could never figure out how to use an ever changing Peukert exponent. Once I obtained a battery monitor I could not tell the monitor how it needs to behave so as to account for the change either.
Can someone explain how we calculate the rate of change, quantify the amount of change, and if we can do those things then how does anyone get any sort of practical use from this exercise?
Charles
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Well I am not a big fan of these meters for reasons such as this. That said I do know some like them and I see nothing wrong with that. I think like a lot of theory about batteries on boats it has to be taken with a grain of salt. I guess you could reset the Peukert every now and then but you might have to use a guestimate. You would also have to change it after a equalization. Maybe there is a happy average that would work for a year or so. For me personally I just monitor voltage and leave it at that but is a gustimate as well. Maine sail you have more experience with these meters have you found that the results change as the batteries age? I guess a long term study would be useful but by the time you finished that they would come out with a new battery type lol Gotta love boats never an easy answer.
Capt. Wayne Canning, AMS
www.projectboatzen.com
Capt. Wayne Canning, AMS
www.projectboatzen.com
The simple answer is you subtract a few % each year off the Ah capacity and leave the Peukert at the factory number. You can also bump the charge efficiency factory a tad each year too if you want.. The real answer is to do a 20 hour capacity test each year if you want a really accurate monitor. Otherwise it is better to err on the side of the batteries and remove more capacity from the Ah capacity setting than they may have technically lost.
I have delved deep into the Peukert programming with a number of battery manufacturers. All of them suggest not changing the Peukert value. Why?
Lets look at a 100Ah battery with a new Peukert of 1.30
Loads below the 20 hour rate:
If we draw that 100Ah battery at 2A we get roughly 135Ah's of capacity
Note: Increases in capacity at slow rate discharge are from mathematical formula and usually do not = actual chemical capacity. Gains at slow discharge rates can range from 105% to 120% (thick plate batteries) of capacity but I've not seen much more...
If we change or increase the Peukert as the battery ages to 1.35 and apply the same load of 2A we now have 138 Ah's of capacity.. This simply can't happen with an aging battery. Batteries don't increase in capacity with age. On sailboats we are normally drawing our banks at well below the 20 hour load so increasing the Peukert does not work..
Loads above the 20 hour rate:
If we draw that 100Ah / P 1.30 battery at 12A we get roughly 77 Ah's of capacity
If we change or increase the Peukert as the battery ages to 1.35 and apply the same load of 12A we now have 74 Ah's of capacity.. This can happen with an aging battery, but what about the other side of the equation shown above.......
This is the simple reason you don't really want to change the Peukert.
I can tell you that our bank of Wal*Mart group 31's started programmed as 370Ah bank but was rated at 375Ah. At the beginning of year six they were programmed for 340Ah's, and tested at 349Ah's, at the end of the sixth season of use. I begin reducing Ah capacity in year one to err on the side of caution. Being at a higher SOC NEVER hurts your batteries.
Personally, for our batteries, I have found programming an Ah reduction of 1% year one, 1.5% year two then 1.75% for each subsequent year works well and keeps our monitor very closely lined up with capacity. Our formula will not work for everyone but has been compared to actual capacity and works for us.
Maine, what a wealth of information you have ! thanks so much for sharing it with all of us, it is much appreciated, it makes a big difference to our understanding of how our systems work and how to optimize them, I hope I bump into you one day so I can buy you a drink or two, or three or.....thanks again, Bob
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