Charging Voltage Question

[Solstice]

At the 5 hour mark the charger is now reading 14.8 and 27.2 amps so it has started its taper. I believe I am set for Flooded which is what I have but the top end voltage has been consistent with what I experience when I return to my slip. After a while she will settle back to 13.2 float (many more hours as Maine Sail indicates)

Blitz did read my mind on the size of my charger ... is there a rule of thumb for charger size to total bank hours? I would prefer not to have to run my charger this much on the mooring.

Although your question is focused on getting Amps back into your batteries, I would suggest one key variable to consider is what your Fridge/Freezer is really consuming.
I have a 355 and I believe you have the same Isotherm that I do. If so, I would suggest that it is consuming many more AHs than you think. I’ve been tracking mine for 9 seasons and honestly it’s the only thing on my boat that I would gladly replace. It’s poorly insulated and due to the positioning of the cold plates, it tends to frost up quickly, which in turn insulates the plates, requiring the compressor to run more, etc.
I’ve tracked my AH consumption using a Victron and that Fridge (not including the freezer) can consume 60-80A in 24 hours, especially in the heat we’ve experienced in the Northeast this summer.
Just got back from a month out spent entirely without shore power and the Fridge was our biggest frustration.
When home we are on a slip. I have a 40A Sterling (same as a ProNautic) and swapped out my factory 4Ds after our 4th season with Rolls 6V.
Just something else to consider...

 

[dlochner]

The refrigerator and freezer burn about 3-5 amp hrs over another 12 hrs

@Solstice has a good point. To clarify what you have written, are you saying that you only use 3-5 amp hours over 12 hours? If so you have a very efficient refrigerator, because that means it is drawing less an ½ amp when running.

I think what you mean is the refrigerator draws 3-5 amps when running. If the refrigerator runs for 12 hours it would have drawn between 36 and 60 amp hours (amp draw times running time). That would put your refrigerator's power consumption in the range that most of us experience. My refrigerator system draws ~29 amps when running, but only runs for about an hour a day, thus I use about ~60 amp hours or a about 15% of my battery capacity per day.

 

[Monterey385]

@Solstice has a good point. To clarify what you have written, are you saying that you only use 3-5 amp hours over 12 hours? If so you have a very efficient refrigerator, because that means it is drawing less an ½ amp when running.

I think what you mean is the refrigerator draws 3-5 amps when running. If the refrigerator runs for 12 hours it would have drawn between 36 and 60 amp hours (amp draw times running time). That would put your refrigerator's power consumption in the range that most of us experience. My refrigerator system draws ~29 amps when running, but only runs for about an hour a day, thus I use about ~60 amp hours or a about 15% of my battery capacity per day.

3-5 amps per hour over 12 hours totaling 36-60 amp hrs plus another 60-90 amp hrs from the time sailing with electronics. My estimated burn was 100-150 amp hrs.

If I understand Maine Sail correctly and if at 4 years I have 90% of my capacity left, then my bulk charge phase would go to about 300 amp hrs (420 x .9 x .8). If my burn was 150 amp hrs then my starting point was 380 - 150 or 230. My bulk phase should have been much shorter than 5 hrs.

I think I either burned a lot more amp hrs than 150 or my battery capacity is now a lot less than 90%.

I’m even more jealous of my buddy’s amp-hr meter now -

Time to break out a spreadsheet!

 

[dlochner]

3-5 amps per hour over 12 hours totaling 36-60 amp hrs plus another 60-90 amp hrs from the time sailing with electronics. My estimated burn was 100-150 amp hrs.

If I understand Maine Sail correctly and if at 4 years I have 90% of my capacity left, then my bulk charge phase would go to about 300 amp hrs (420 x .9 x .8). If my burn was 150 amp hrs then my starting point was 380 - 150 or 230. My bulk phase should have been much shorter than 5 hrs.

I think I either burned a lot more amp hrs than 150 or my battery capacity is now a lot less than 90%.

I’m even more jealous of my buddy’s amp-hr meter now -

Time to break out a spreadsheet!

What kind of electronics are you using? 100 amp hours is a lot of current usage in 12 hours. Do you have digital ammeter, so you can measure what you actually draw?

Your bulk charging calculations are off a bit. .2C for a 420 amp hour battery is 84 amps in bulk stage, or 20% of the amp hour capacity.

While the charger may be putting 50 amps into the battery, there is some loss of efficiency, so not all of the 50 amps is actually charging the battery, some of it is lost to heat and other factors. As the battery approaches a full charge, the ability of the battery to absorb the charge decreases and becomes less efficient. Thus if you draw 50 amp hours out of the battery, it will take longer than 1 hour at a 50 amp charge to bring the battery back to its starting charge level. This is demonstrated by Peukert's Law.

 

[dlochner]

Dave, what happens to the extra charger output when the loads are removed such as a fridge? Potentially could this not cause the battery’s max charge current to be exceed?

While I was sitting here, my high current draw refrigerator just kicked on. Here's what happened.

The battery's were at 100% SOC with a very small load, <1 amp. The charger was in float stage just meeting the 1 amp load.

When the refrigerator started, there was an immediate 29 amp draw, the charger then started increasing its output to match the draw, reaching 30 amps at 13.6 v resulting in .70 amps going back into the battery.

After the refrigerator stopped, the charger slowly decreased its output until it reached the float stage again with about a 1 amp charge.

For monitoring I have a Balmar Smart Gauge, a Victron Battery Monitor (used to monitor actual usage), and a remote panel for the ProMariner 1250 that shows charge voltage and current.

 

[Monterey385]

To recap some of the information:

1. I have a ProNautics 12-30P which charges at a maximum rate of 30 amps net any draw during charging. I am estimating the charger output approximately 25 amps over a 5 hour period accounting for a 3-5 amp draw periodically from the refrigerators during charging. At the 5 hour point, the charger began to reduce amp output which I am interpreting to mean the charger ended the "bulk phase". If I am interpreting dlochner's note regarding .2C properly, then at 25 amps I should have been well below the threshold of .2C.

2. My electronics package includes a 12 inch Raymarine MFD, four instrument displays including an autopilot head, Radar, VHF, Sirius Weather, Stereo, AIS Transponder. In addition I have a refrigerator and a freezer. I estimated 15Amps per hour for 6 hours totalling 90 amp hours. Then I estimated 12 hours overnight on just the refrigerators at 3-5 Amp Hours with a top end of 60 amp hours. Together 90+60 = 150 Amp Hours.

3. Having loaded this information into a spreadsheet, I think what I might be dealing with is batteries that are now down to 60% of original capacity and I might have been a bit low in my amp-hr burn estimate. Assuming my 12.1 was indeed accurate and not an unusually low reading, this translates to a 176 AH burn and a 5 hr return to 80% of current capacity (60% of 420 or 252 AH X .8 = 200 AH). In other words, 252 AH - 176 AH burn + 125 AH bulk charge over 5 hours = 201.

I'm going to recheck the batteries today to make sure my 210 AH per battery is accurate.

Returning to the original set of questions, I was trying to validate whether the 12.1 was an accurate reading ... I'm beginning to think it was close to reality.

 

[Solstice]

To recap some of the information:

1. I have a ProNautics 12-30P which charges at a maximum rate of 30 amps net any draw during charging. I am estimating the charger output approximately 25 amps over a 5 hour period accounting for a 3-5 amp draw periodically from the refrigerators during charging. At the 5 hour point, the charger began to reduce amp output which I am interpreting to mean the charger ended the "bulk phase". If I am interpreting dlochner's note regarding .2C properly, then at 25 amps I should have been well below the threshold of .2C.

2. My electronics package includes a 12 inch Raymarine MFD, four instrument displays including an autopilot head, Radar, VHF, Sirius Weather, Stereo, AIS Transponder. In addition I have a refrigerator and a freezer. I estimated 15Amps per hour for 6 hours totalling 90 amp hours. Then I estimated 12 hours overnight on just the refrigerators at 3-5 Amp Hours with a top end of 60 amp hours. Together 90+60 = 150 Amp Hours.

3. Having loaded this information into a spreadsheet, I think what I might be dealing with is batteries that are now down to 60% of original capacity and I might have been a bit low in my amp-hr burn estimate. Assuming my 12.1 was indeed accurate and not an unusually low reading, this translates to a 176 AH burn and a 5 hr return to 80% of current capacity (60% of 420 or 252 AH X .8 = 200 AH). In other words, 252 AH - 176 AH burn + 125 AH bulk charge over 5 hours = 201.

I'm going to recheck the batteries today to make sure my 210 AH per battery is accurate.

Returning to the original set of questions, I was trying to validate whether the 12.1 was an accurate reading ... I'm beginning to think it was close to reality.

I think your assumption in point #3 above is correct. The Exide 4Ds that came from the factory are dual purpose and average at best. I use a factor of reducing usable capacity by 5% per season when calibrating my Victron every season (credit to @mainesail). I believe you said your on your 4th season with the batteries, so I suspect you have a lot less usable capacity then you assumed..

 

[Stu Jackson]

I’m even more jealous of my buddy’s amp-hr meter now -

Jealousy isn't good for your mental health.
A Victron BVM702 is less than $200 and much better and easier to install than a Xantrex (I wouldn't touch any of their products these days --- for the past decade or more --- even if someone gave one to me for free. Any of their products.
I have a Heart Interface Link 2000 that I installed in 2003 or so and learned how to use properly well before Maine Sail published his articles on algorithms.
Just for grins and giggles:

Time to break out a spreadsheet!

I thought it prudent earlier this season to confirm my battery bank's performance, so I began an hourly monitoring regimen when anchored out for two nights and three days.
I made up the attached spreadsheet. [I couldn't upload the spreadsheet XLS file, so the headings are at the bottom of this post.] It's just blank using gridlines for ease of use and clarity.
It confirmed my use based on my "normal" use simply because when I took the readings I was doing what I do normally at anchor.
I don't have solar or a generator, so I also confirmed that I can put 23 to 30 ah BACK into my 390 ah house bank when I run the engine out of gear at 1500-1800 rpm for an hour with my 100 A alternator and MC-612 external regulator with no de-rating with belt/amp manager. I use Small Engine Mode to reduce the AO when the bank is low and I first start motoring at cruising speed.
My fridge uses 60 ah / day and my daily energy budget is 100 ah.
Sometimes I go all three days without running the engine, other times I run it the first evening or next morning if I think I'm going to stay longer.
My charger is a Heart Interface Freedom 15, 1500W inverter, 75A charger.

Spreadsheet headings:

DAY DATE TIME Volts Amps AH AH/Day (or hour) Fridge Invrter Stereo Batts Phone VHF REMARKS

The individual items are just for check marks as to what was I or O. Batts are for charging my rechargeable batts for my GPS handheld. VHF is for the hh when plugged in for use the next day. Invrtr at anchor is when I want to watch a movie on my laptop.

It takes a few days of discipline to do it hourly, but heck, whatcha got to do at anchor anyway!?!?!

Good luck, it's worth the effort. I feel more comfortable always cross checking my assumptions.

 

[JimInPB]

... if at 4 years I have 90% of my capacity left, ...
...I think I either burned a lot more amp hrs than 150 or my battery capacity is now a lot less than 90%....

I would expect that it would be likely for a 4 year old bank to have a lot less than 90% capacity remaining.

 

[Stu Jackson]

I would expect that it would be likely for a 4 year old bank to have a lot less than 90% capacity remaining.

Why?
If properly cared for, and little if no PSOC conditions, that shouldn't be "normal."
My bank is from 2014 and I simply don't see that condition, given my last detailed post.

 

[JimInPB]

Why?
If properly cared for, and little if no PSOC conditions, that shouldn't be "normal."
My bank is from 2014 and I simply don't see that condition, given my last detailed post.

Batteries are consumables. In my experience, even well cared for banks deteriorate over time. My best bank life so far was 8 years from new to fully unusable.

 

[Monterey385]

I don't have solar or a generator, so I also confirmed that I can put 23 to 30 ah BACK into my 390 ah house bank when I run the engine out of gear at 1500-1800 rpm for an hour with my 100 A alternator and MC-612 external regulator with no de-rating with belt/amp manager. I use Small Engine Mode to reduce the AO when the bank is low and I first start motoring at cruising speed.
My fridge uses 60 ah / day and my daily energy budget is 100 ah.

Stu - I’ve been meaning to ask, I have the factory original alternator, SG10S078. I think it’s 75 Amps. How many amps for recharging during bulk phase should I expect when running the engine at cruising speed, say 2,500 RPM or 80%

 

[jssailem]

Monterey I expected 70% (possibly a little high) when cold and starting. And as the alternator got hot more like 40-50%. Then of course there are the acceptance limits of the batteries, which have been covered earlier.

 

[NotCook]

? I would prefer not to have to run my charger this much on the mooring.

You may want to consider so solar. We have 420 watts of solar from 4 panels in parallel: One on the davits, one on top of the pilot house, and one on each side of the "cockpit"/quarterdeck. Most of the time at least one of them is shaded by something, such as mast, booms, etc., but we have seen as much as 20 amps pumping in from them midday. The boat is on the mooring always, with the SeaFrost running, and the batteries always full except first thing in the morning, obviously. We haven't used the generator for 2 years. I should try to start it to just make sure its ready...

 

[Stu Jackson]

Stu - I’ve been meaning to ask, I have the factory original alternator, SG10S078. I think it’s 75 Amps. How many amps for recharging during bulk phase should I expect when running the engine at cruising speed, say 2,500 RPM or 80%

Basic charging 101 says that the alternator should be putting max current out as the voltage rises to the regulator's voltage set point. That's THE definition of bulk.
The duration of the current will depend on how depleted the bank is.
That's why folks with large banks that can accept a LOT of current use belt manager or in my case Small Engine Mode to reduce the load on the alternator until the amps drop to keep the alternator cooler. SEM is just the manual way of using the alternator temp sensor connections on the external regulator I have.
Small Engine Mode - discussion with link to the picture of the toggle switch: http://c34.org/bbs/index.php/topic,4454.msg27149.html#msg27149

Small Engine Mode - the picture of the toggle switch http://c34.org/bbs/index.php/topic,4669.0.html

 

[dlochner]

Stu - I’ve been meaning to ask, I have the factory original alternator, SG10S078. I think it’s 75 Amps. How many amps for recharging during bulk phase should I expect when running the engine at cruising speed, say 2,500 RPM or 80%

If the alternator has an internal regulator, not that much. The regulator is set to protect the alternator and batteries from excessive heat and so reduce the output by setting a voltage limit. On the MarineHowTo website there is an article about this: https://marinehowto.com/automotive-alternators-vs-deep-cycle-batteries/

 

[Monterey385]

If the alternator has an internal regulator, not that much. The regulator is set to protect the alternator and batteries from excessive heat and so reduce the output by setting a voltage limit. On the MarineHowTo website there is an article about this: https://marinehowto.com/automotive-alternators-vs-deep-cycle-batteries/

This made perfect sense and as usual my situation is a hybrid 60% of the time we are daysail/dockside and 40% of the time we are mooring/anchoring/cruising. My issues have been when we are mooring/anchoring/cruising and this season I think my batteries have started to gas when the charger brings them to 14.7 for the absorption stage. This also explains why even after a 1hr 15 min engine run from mooring to dock my dockside charger will work for hours at full output after a long daysail.

I think it’s time to start planning my next 4-5 year system. As usual, everyone on this board is fantastic. Thank you.

 

[dlochner]

I think it’s time to start planning my next 4-5 year system. As usual, everyone on this board is fantastic. Thank you.

Check the Musings with Maine Sail forum on SBO. There are many discussions on how to create a good simple DC electrical system.

 

[Stu Jackson]

A lot of those Maine Sail links are also here:

Electrical Systems 101 http://c34.org/bbs/index.php/topic,5977.0.html

 

[Stu Jackson]

I had a nice afternoon conversation with a fellow sailor yesterday afternoon, another nice skipper I had finally met in person after just internet forums.

We discussed this very issue. Of course, solar is THE way to go to reduce loads on alternators. It reduces the depth of discharge of any bank. Period.

But after an hour or two discussing internal vs. external regulators (yes, yeah, I've real Maine Sail's material on this, it's all in my Electrical 101 link), once one understands how VOLTAGE regulators work, the only REAL answer to how much an alternator has to "put out" on engine startup, regardless of rpm, is simply based on the battery bank's ACCEPTANCE.

My new friend has the same size bank that I do. Nominal 400 ah house bank, ACR/VSR/combiner for start/reserve bank. Doesn't matter.

What DOES matter is the TYPE of battery.

I have wet cells. As Maine Sail and I have repeatedly mentioned, the nominal ACCEPTANCE of this size bank with wet cells is 50 A for a bank at 50% SOC, around his 12.1V. That's is what I see from my 100A alternator, as well as from my Freedom 15 I/C, with a 75A charger. I just came back to my slip, plugged in and started the charger. It went to 75 amps on my link for all of a few minutes and then settled at bulk at around 50A.

My friend's question to me was simple: "What should I expect out of my 80A alternator at 50% SOC?" So I told him what the last paragraph said.

But then he said, "My bank is AGM."

I replied, "The answer is DIFFERENT for different battery types. Your AGMs can ACCEPT much more current than wet cells."

It is THAT SIMPLE.

Regardless of charging source, regardless of type of regulator (internal external), regardless of how you control your regulator's signal (Belt Manager, Small Engine Mode) both of which deliberately REDUCE alternator output, the answer is that the type of bank will determine the amount of current that a bank can ACCEPT.

Battery acceptance is THE answer.

The duration of the bulk phase or stage will be determined by the size of bank, type of bank, % of SOC and the size of the charging source.

For any given TYPE of battery chemistry, the outcome is identical. Nominal 400 ah house bank (very normal for us mid-sized cruisers) and same SOC from however long the bank has been working:

Small alternator or small shorepower charger: will max out and get hot without temperature sensing or Belt Manager or Small Engine Mode from an external regulator, and will run max current on shorepower. Small is defined as anything BELOW the bank's acceptance at that SOC.

That's why we have been recommending larger alternators, which can work less hard when taxed to output max current.

It is really that simple, which is supported by all the discussions about the regulation of ANY charging source, alternators, shorepower chargers or solar and their controllers.