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Amp hours and voltage

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Category: Hints & Tips
Forum Name: 415/418
Forum Description: 415/418 Hints, Tips and News
URL: https://www.myhanse.com/forum_posts.asp?TID=10866
Printed Date: 19 March 2024 at 11:27
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Topic: Amp hours and voltage
Posted By: Jeremy
Subject: Amp hours and voltage
Date Posted: 01 July 2018 at 08:12
Hi Guys,
I have the standard 415 battery setup (2 x 165ah batteries so 330ah) and Ive recently installed a BEP battery monitor. 
Over winter Ive found we are drawing a lot more power over night with fewer day light hours and less effectiveness in solar charging. By morning we are getting very low on power, the displays are showing approx 11.9V in the house system. But here's the issue. The BEP monitor is showing we are down to 11.9V but also saying that we have 300ah remaining. Thats 90% charged! Ive heard these AGM batteries are good till about 50% charge. So im rushing to get the motor started because im seeing 11.9V.
Im not sure of the relationship between V and Ah, who should I trust? My batteries are the original ones (2014) Maybe they're nearing their use by date?

Thanks heaps!



Replies:
Posted By: charentebob
Date Posted: 01 July 2018 at 10:07
Does the BEP also monitor the starter battery? You mention rushing to start the engine as the battery was 11.6v. Some monitors assume 100% when fully charged at installation even if though the batteries are not new. It may be worth having an electrician check once you have charged well to have a datum point. My batteries are 5 years old & OK. Last year I installed a Victron digital amp meter & Colour display. This displays the solar, engine charging & shore power inputs & discharge. Now I can ensure that the batteries never get below 80% which will hopefully prolong their life.

Incidentally I had to replace the engine starter battery and changed its location to below the port side rear berth. I replaced with a good quality sealed starter battery. The original location get too hot and an AGM is not the best battery for starting. The good news is that this mod can be achieved without altering any of the cabling.


Posted By: Ratbasher
Date Posted: 01 July 2018 at 18:24
While battery monitors are useful, the only definitive check is with a multimeter measuring voltage directly at the terminals. As a guide:

100% - 12.7-13.2v
75% - 12.4v
50% - 12.2v
25% - 12v
Disch/flat - =< 11.8v

If the multimeter confirms you're on 11.9v then ignore the AH reading from the monitor and recharge asap.  You must have a separate engine start battery; after you've been using the domestic bank for a while check that the engine start is showing a different (hopefully higher!) voltage.  If at the same voltage as the house bank then its' not isolated and you might soon be practicing docking under sail.  If it is properly isolated then you needn't be concerned about starting the engine.

I'm afraid it sounds like you might have missed something on setting up the BEP and calling in an electrician is not a bad idea.  Monitors need to be programmed specifically for the house batteries and should not include the engine battery unless it has dual capability.  The readings are curious - perhaps the AH rating of the engine start was included while voltage monitoring was just of the house bank?!?  

Good luck! 





-------------
H400 (2008) 'Wight Leopard', Gosport UK


Posted By: Ratbasher
Date Posted: 01 July 2018 at 18:35
Forgot to add that if the multimeter confirms you're down to 11.9v overnight then you've either suddenly developed a bad drain or your batteries are indeed shot.  I'd expect AGMs that have been looked after to last at least 5 years though.  Do check that your charger is set for AGMs and not lead acid as the former demands a lower voltage during the bulk-charge phase.  

-------------
H400 (2008) 'Wight Leopard', Gosport UK


Posted By: Jeremy
Date Posted: 01 July 2018 at 19:32
Very useful information! My assumption is that the BEP monitor is set up wrong in the house Ah reading and should have been showing around 50%, not 90%. 
Im also assuming that my batteries may be on their way out as I've never struggled to get them through the night without dropping to an alarmingly low level just running the usual items, fridge, lights.

Can anyone else tell me what they would expect to pull in a night? either in V or Ah.
Thanks again.


Posted By: Ratbasher
Date Posted: 02 July 2018 at 09:29
Hi again Jeremy

I recently did an audit of power usage on my own boat.  Unsurprisingly, in the present run of hot weather in the UK the fridge was the biggest culprit running for 2 mins every 20 and drawing just over 6AH when operating.   Evenings alongside, the TV/PC combined usage was about 10AH but the drain from the LED lights was only about 0.1AH each. With the size of your bank at 330AH similar usage should certainly leave a voltage very far above the reading of 11.9 that you're getting now.  

Strongly recommend checking with a multimeter, though.  They cost peanuts but can save you a packet(!)

Interesting to hear the experiences of others.

Rat






-------------
H400 (2008) 'Wight Leopard', Gosport UK


Posted By: Samtutuki
Date Posted: 02 July 2018 at 10:29
It might be worth exploring this type of battery monitor:

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



Posted By: Samtutuki
Date Posted: 02 July 2018 at 10:33
And this is an interesting article too:

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


Posted By: Touch of Grey
Date Posted: 02 July 2018 at 14:54
Jeremy


I replaced my service batteries (2 * 165 Ah Victron AGMs) like with like a year ago, installed a Balmar SmartGuage (the device Samtutuki mentions) at about the same time and have been monitoring battery performance closely for the last month.


Between 10pm and 7am I am seeing a drop of between 0.15 and 0.25 volts with the SmartGuage saying capacity has dropped between 5% and 15%. During this time, the Isotherm fridge will be drawing 4 amps (according to the manual) or 6 amps (Ratbasher) when the compressor is on,  the Waeco CFX50 fridge will be drawing 8 amps when the compressor is on, and we’ll have at least 4 electronic devices charging.  The inverter which draws 0.25 amps with zero load and the gas solenoid which draws 0.8 amps will both be off. Overnight the temperature has been 15-20C.


If I assume that my total battery capacity is now 300 Ah (a drop of 10% since installing them) and that, on average, I am using 10% of this capacity overnight then that’s 30 Ah over 9 hours or about 3.3 amps per hour.



-------------
Allan Fraser


Posted By: Jeremy
Date Posted: 02 July 2018 at 20:16
Thanks for your help guys, all useful and exactly what I was looking for. I put my multi meter on the batteries, did a few tests and they have indeed met a fast demise over the past few months. Im taking them to a battery clinic who claim they can rejuvenate them. Failing that i'll be up for new ones and will probably add 100ah at the same time.


Posted By: Rubato
Date Posted: 03 July 2018 at 17:17
Jeremy, that battery rejuvenation stuff is BS unfortunately.
Have you double checked your shore charger (and smart charger off the alternator if you have one) to make sure they are properly set for AGM? That can toast the batteries pretty quick if not set properly.

On our 400 the fridge is the big culprit. We find a capacity a challenge if we anchor early in the day (say 1 or 2pm) and are running the stereo, some electronics, the fridge, the stove (gas valve), etc. for the rest of the day. We shut it all down when going to bed, except the fridge and the LED anchor light, then there will be not much capacity left in the morning - battery sitting very close to 12V (50%). Note that the voltage is to be measured with little to no load. For example, it will read even lower when the fridge is on.

If I do anchor early, I try to run the engine for 20-30 minutes to add a bit of charge in so there is more capacity left in the morning, works like a charm.


-------------
Steve

Hanse 400e, #168


Posted By: Jeremy
Date Posted: 03 July 2018 at 21:35
Thanks for that! Id assume the charger is set for AGM, as I haven't had a problem until now and the batteries have been in the boat since new (2014). But this is worth checking.
We had an incident some weeks back. The Sterling VSR negative terminal came loose so it never measured a voltage from the batteries therefore when we started the engine the batteries didnt start charging. We sailed to our destination, started the motor the next day and pretty soon I realized the house voltage had suddenly dropped to 10.5V on starting nav, engine blower etc. I shut everything down and continued to sail and worked through the problem. Solar slowly brought power back up. But the damage may have been done.



Posted By: charentebob
Date Posted: 16 July 2018 at 12:43
I can recommend the Smartgauge. Fitted one for the Bow Thruster battery when it seemed to being overcharged by the B/B charger. I spoke to Sterling Power about this & they recommended setting the charger to the lowest output. Then I installed a switch in the charging line so that I could isolate the charger from the BT battery. I monitor this metre and throw the switch when it indicates 100% charge. I decided that this was a cheaper option to changing the B/B charger if there is a fault in it’s ability to cut-out when the battery is full.

Nigel


Posted By: spam
Date Posted: 17 July 2018 at 04:19
For those using the Balmer Smartgauge,  what battery type do you have it set to?   I love the Smartguage for its simple install (no shunt, just two small wires, no calibration) and operation (one button with SOC), but the one thing that has never been really clear to me is what battery type to set it to (the only setting required).   AGM seems to be the logical choice but I actually set it to #1 (wet cell) after reading the manual:

NOTE There are actually two very distinct types of AGM batteries with very different operational characteristics. In one type the only real difference is that the electrolyte is held in a glass matt. This type usually have charge voltages very similar to flooded wet cell batteries. The off load terminal voltages will also be very similar to flooded wet cell batteries. If your AGM batteries are of this type then SmartGauge should be set to battery type 1 The other type of AGM has additional chemicals in the battery (similar to gel cell batteries) and this type usually require lower charge voltages and the off load terminal voltages will be similar to gel cells. This type require SmartGauge to be set to battery type 3

I have the standard 2 * 165 Ah Victron AGM set up and based on what I can tell from the Vitron website, the terminal voltage are more similar to flooded wet cell batteries so I set is to BT1, however I am still not completely sure this is the correct setting.  Does anyone know the real answer to this?  Has anyone checked with Victron?  What have other set the smartgauge to?


Posted By: charentebob
Date Posted: 17 July 2018 at 07:50
The Smartguage i have is connected to a Optima Bluetop Spiral-wound AGM. To be frank I can’t remember which setting I used. I think I might need to ask the supplier again to ensure it’s right.


Posted By: Black Diamond
Date Posted: 17 July 2018 at 12:31
A lot of good information in this thread.   One point of disagreement, however.   A few have talked about ONLY using voltage and an external multimeter to determine state of charge.    I've seen too many batteries go from 12.5 volts down to 10.8 volts in a few minutes because of bad cells, sulfation, or other issues.  A real monitor, counting amps and other factors like temp seems the only way to go.

FWIW


-------------
Rick
S/V Black Diamond
Hanse 575 Build #192, Hull# 161
Newport, RI


Posted By: charentebob
Date Posted: 17 July 2018 at 14:49
I agree. Volts only tells part of the story. I installed a Victron Energy Digital amp meter linked to a Colour Display. This shows the state of the House batteries, output of inverter, shore power and solar output. Absolutely great. It’s alerted me to the fact that the solar is producing a lot less than it did & so I am now investigating why. Would not know otherwise.


Posted By: Black Diamond
Date Posted: 17 July 2018 at 18:18
Monitoring makes it far easier to work with your batteries and energy producing devices (Solar, alternator, generator, shore power charger), and a decent monitoring system is a must for a sailboat. I have the SIMARINE boat monitoring system.  It handles both producing and consuming device monitoring as well as tanks and temperatures.

Its a pretty extensible system,  similar to the Philippi system, but with a bit newer technology...

See pictures...













-------------
Rick
S/V Black Diamond
Hanse 575 Build #192, Hull# 161
Newport, RI


Posted By: StavrosNZ
Date Posted: 18 July 2018 at 00:35
Hi Jeremy sounds like your batteries are on the way out, short life considering the age of your boat so check that your shore power charger is set for AGM profile charging and that your solar panel regulator profiles are correct.

On Villanelle i upgraded to high output alternator (140 amp) and serpentine belt and pulleys, after a night at anchor which normally consumes 55amps or thereabouts i am fully recharged in 20 minutes of motoring. High output alternator is by far best return in terms of money you can sped to get amps you need. Solar great for topping up but not replacing large charge amounts.


-------------
Stephen
2010 H400 #691, Auckland, New Zealand


Posted By: Jeremy
Date Posted: 18 July 2018 at 08:02
Thanks Stephen. Ive just replaced the batteries. Gone to 444 amp hours. One of the old batteries had a capacity of 35ah and the other 41ah, so they were well gone. Still not sure why. I checked the charger. Its set to AGM. For now I've disconnected the solar panels. Yes I guess your right. 20min of diesel is nothing for a full charge! Did you have to change belts / pulleys? Why couldn't you just bolt on a bigger alternator? Where did you get it?
I had a phantom amp draw too of around 0.3a +. Ive determined the cause of most of that, just 0.12 amps unaccounted for.


Posted By: Black Diamond
Date Posted: 18 July 2018 at 12:29
Usually there is "Peukerts Exponent" (or whatever its called) to be set as a variable to the charger/monitor which affects the way it charges and / or counts amps.   Have you looked at the manual for proper setup of the variables for your batteries and charging system?



-------------
Rick
S/V Black Diamond
Hanse 575 Build #192, Hull# 161
Newport, RI


Posted By: Rubato
Date Posted: 18 July 2018 at 20:57
Originally posted by Black Diamond Black Diamond wrote:

Usually there is "Peukerts Exponent" (or whatever its called) to be set as a variable to the charger/monitor which affects the way it charges and / or counts amps.   Have you looked at the manual for proper setup of the variables for your batteries and charging system?


Peukert's can be input on some battery monitors but it has no affect on charging.


-------------
Steve

Hanse 400e, #168


Posted By: StavrosNZ
Date Posted: 18 July 2018 at 23:03
Jeremy, i did a post on the upgrade as follows:

http://www.myhanse.com/alternator-upgrade_topic10185.html



-------------
Stephen
2010 H400 #691, Auckland, New Zealand


Posted By: StavrosNZ
Date Posted: 18 July 2018 at 23:24
stereo has permanent power to retain stations, bilge pump, one overhead light normally and alternator smart regulator likely to have permanent supply as well.

Solar properly regulated will keep these looses accounted for and batteries topped up but an efficient alternator/regulator remains best most efficient way to keep your charging up.

Don't leave shore power on permanently either in my experience this reduces battery life and increases risk of other issues (electrolysis etc).


-------------
Stephen
2010 H400 #691, Auckland, New Zealand


Posted By: Mike2145
Date Posted: 19 July 2018 at 09:31
Originally posted by Jeremy Jeremy wrote:

Thanks Stephen. Ive just replaced the batteries. Gone to 444 amp hours. One of the old batteries had a capacity of 35ah and the other 41ah, so they were well gone. Still not sure why. I checked the charger. Its set to AGM. For now I've disconnected the solar panels. Yes I guess your right. 20min of diesel is nothing for a full charge! Did you have to change belts / pulleys? Why couldn't you just bolt on a bigger alternator? Where did you get it?
I had a phantom amp draw too of around 0.3a +. Ive determined the cause of most of that, just 0.12 amps unaccounted for.


Remember adding a high capacity alternator on its own will have little or no advantage. It need to be coupled with. Charger and battery bank that can make use of the available power. Most smart chargers can do this but do check. I’ve seen many high output alternators fitted without updating the downstream components. And it’s made no difference. The rating is the maximum it ‘can’ produce not what it will. It is the charger and battery pack that determines what will be generated by the alternator the alternator can only do what it’s asked to do up to it’s rated ability. Matching what the battery bank can accept at a maximum charge rate controlled by the charger (plus other ancillaries) with what the the rated output of the alternator is the key (plus a bit to keep the stess down on the system) is the key.
Have a look at other threads on the subject there is a lot of information on this and other forums.

Ignore me if you already know all this stuff!

Mike

-------------
Cant take a joke, don't buy a boat.


Posted By: StavrosNZ
Date Posted: 19 July 2018 at 21:36
agreed Mike, smart regulator and cable sized for higher output and battery bank accordingly. Also replaced shore power charger at the same time with new Pro Mariner Pro Nautic charger that also has ability to act as power supply to the boat sockets without charging as setting.

-------------
Stephen
2010 H400 #691, Auckland, New Zealand


Posted By: Rubato
Date Posted: 20 July 2018 at 17:32
Originally posted by StavrosNZ StavrosNZ wrote:


Don't leave shore power on permanently either in my experience this reduces battery life and increases risk of other issues (electrolysis etc).

If you don't keep shore power attached to trickle charge your batteries, the trickle charge needs to come from somewhere else (possibly solar as you mentioned above). Lead acid batteries in particular have a fairly high rate of self discharge which can also destroy battery life. 


-------------
Steve

Hanse 400e, #168


Posted By: Jeremy
Date Posted: 21 July 2018 at 21:18
Hi,
Yes Ive inputted the correct perkets number. This seems to have improved ah accuracy. I took the new batteries for a test run last night. Seems we use about 50ah over night and in the morning were on about 12.7V to 12.8V. This was verified by the multi meter.

Thanks!!


Posted By: Jeremy
Date Posted: 21 July 2018 at 21:21
Yes thanks for that. Im not going to track down the last 0.1A of loss. Just put it down to those items. It seems everything is functioning properly again now with new batteries and property set up monitor.



Posted By: Mike2145
Date Posted: 06 September 2018 at 09:52
Originally posted by Jeremy Jeremy wrote:

Hi Guys,
I have the standard 415 battery setup (2 x 165ah batteries so 330ah) and Ive recently installed a BEP battery monitor. 
Over winter Ive found we are drawing a lot more power over night with fewer day light hours and less effectiveness in solar charging. By morning we are getting very low on power, the displays are showing approx 11.9V in the house system. But here's the issue. The BEP monitor is showing we are down to 11.9V but also saying that we have 300ah remaining. Thats 90% charged! Ive heard these AGM batteries are good till about 50% charge. So im rushing to get the motor started because im seeing 11.9V.
Im not sure of the relationship between V and Ah, who should I trust? My batteries are the original ones (2014) Maybe they're nearing their use by date?

Thanks heaps!

Just to answer the original question of the relationship between V and Ah.  The short answer is none directly, its a % of the total so  unless you know the total available Ah of the battery you cant say what % in Ah remains or has been used.  The voltage drops at a predictable rate (for a battery in reasonable condition) and therefore at certain voltages we can say that the battery is at x% charge.  The list below is a reasonable, if a bit pessimistic, set of numbers to work from. So we can say that when the battery is at 12.6v its about 50% discharged.  So in your case the 330Ah total has used 115Ah. (the 330 would be very optimistic even for a new battery) NOTE:  These voltage readings should be taken off load and after the battery has rested.  The voltage will reduce when on load giving  false reading.  So measure when there is no or minimal load to get a rough idea of the state of charge. 
If the battery is showing 11.9 with minimal or no load then they are flat.  Ignore the battery monitor.

The advantage of a good  (expensive!!) monitor is that it will be able to do some cleaver maths, using a set of numbers similar to below, to start to work out what the actual capacity of the battery bank given charge/discharge amps is and give a readout of available capacity and state of discharge in a Ah or % display as long as the thing is set up correctly. However,for that money I can do the maths myself!


Hope that helps?



Image result for agm voltage verses capacity chart


-------------
Cant take a joke, don't buy a boat.


Posted By: High Time
Date Posted: 06 September 2018 at 12:57
Originally posted by Jeremy Jeremy wrote:

Yes thanks for that. Im not going to track down the last 0.1A of loss. Just put it down to those items. It seems everything is functioning properly again now with new batteries and property set up monitor.

Hi Jeremy

Did you 'find' the last 0.1A discharge? 

If not then it could be that the zero reading on the monitor has not been set correctly. Some monitors (my Victron included) have a parameter for the zero current reading (in/out) that can be adjusted. Might be worth checking if your monitor can be adjusted for this.

It is worth setting this correctly if possible, otherwise over time when the boat is not in use, the amp hours consumed can be way out.

0.1A per hour = 2.4Ah per day = 72Ah per month


-------------
Roger

High Time (415 #038)


Posted By: Joey D
Date Posted: 06 January 2019 at 14:05
Would anyone we able to advise the proper number setting for the digital multi control on my Victron Energy board?
I always leave the unit switched to on with a setting of 22. Truly appreciate the help




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