2008 helmsman 38- cruising battery management

[capran]

Lugger 85hp engine, engine driven 160amp alternator to house bank, Rolls 820 AH series 5000 6 volt (2),so 12 volt house is 820 AH. Have the BMV 702 victron battery monitor. As an example, after sitting for 2 days (48 hours) from batteries reading totally full 100%. After 24 hours, voltage is 12.51 with fridge off and 12.47 with fridge on, used 58 AH and battery is 95.7%. Another 24 hours goes by and battery is 12.22 volts with fridge off and 12.17 volts with fridge on, with total142 AH used and battery at 89.7%. Would not the voltage be higher with only 11% of the battery used. When I'm moving every day, voltage at rest is always 12.55 or so, but the second 24 hours of 48 brings it down to 12.22ish. ( batteries are new ). Just wondering what others find when out on the hook.

 

[Jeff F]

This might be helpful.
https://support.rollsbattery.com/en...ticles/10372-voltage-readings-state-of-charge

Sent from my moto g play (2021) using Trawler Forum mobile app

 

[twistedtree]

The big Rolls batteries need a very long absorption time. I had a set for my house previously and had a lot of trouble getting then charged and keeping them charged. The long and short is that it's not possible to charge them per Rolls specs using solar because there aren't enough hours of sunlight in the day. After much back and forth with the company, I ended up with a very high bulk/absorb charge. As I recall it was just under 30V for a 24V system, so almost 15V for a 12V system. That was the only way to get them charged over the course of a day. I had plenty of solar - the batteries just wouldn't accept it unless force fed.


It's possible that your underway-charging is suffering similarly.

 

[capran]

Thanks for the link. I'll have to get a wifi signal to download onto a document that I can read and reread.

 

[capran]

Today we motored for 5 hours so going to pay close attention to see how it behaves. 30 minutes after stopping the motor we're at 12.97 volts. 45 minutes after shut down of motor we're at 12.9 v. After 2 hours, of motoring today the amp hour was at zero, meaning it had charged the 144 AH I had used over the prior day. After that, it was still charging at 30 amps for hours 3 thru 5 for the day. It could be like you suggest. Maybe I was assuming that the AH charged, when it zeroed out (not showing any negative number) was fully charged. But maybe zeroed out really isn't necessarily fully charged
. I hour after shut down volts are at 12.89. Maybe even though the BMV702 says 100%, perhaps the battery is not really fully charged, hence the lack of voltage holding longevity

 

[fractalphreak]

Today we motored for 5 hours so going to pay close attention to see how it behaves. 30 minutes after stopping the motor we're at 12.97 volts. 45 minutes after shut down of motor we're at 12.9 v. After 2 hours, of motoring today the amp hour was at zero, meaning it had charged the 144 AH I had used over the prior day. After that, it was still charging at 30 amps for hours 3 thru 5 for the day. It could be like you suggest. Maybe I was assuming that the AH charged, when it zeroed out (not showing any negative number) was fully charged. But maybe zeroed out really isn't necessarily fully charged
. I hour after shut down volts are at 12.89. Maybe even though the BMV702 says 100%, perhaps the battery is not really fully charged, hence the lack of voltage holding longevity

I have a Victron BMV-712, but my understanding is the below detail applies to both - my manual includes both.

You have to watch the BMV-702 and what it says regarding state of charge. If you read close in the manual, the BMV-702 does not reset based on amp hours back into the batteries, but rather on the number of charging amps going into the batteries as a charge rate. There is a setting for this number, and what it will do is reset itself to 100% when the batteries still need charge, but the number of amps charging is at a set percentage. That set percentage is a function of the set battery bank size, so its important to ensure that setting is correct as well. I rely more on an actual reading of amps in (for example, when running my generator I look to see if my charger is bulk charging, absorb charging and what the number of amps are. I usually time it so I'm considering the batteries as charged as I can practically get around the time the AC charger is going to or switches to float). This could also interface with how your alternator's regulator is programmed to charge the batteries. It also could be that when you are sitting at idle the charge amps are low enough for long enough it will reset the charge state on the Victron.

Below is some text copied from the manual. The tail current is the charging amp threshold that resets the Ah percentage and Ah counter, and the charged detection time is how long that voltage must be detected before doing those resets:

03. Tail current
Once the charge current has dropped to less than the set tail current (expressed as
percentage of the battery capacity), the battery is considered as fully charged.
Remark:
Some battery chargers stop charging when the current drops below a set threshold. The tail current must
be set higher than this threshold.
Default Range Step size
4% 0,5 – 10% 0,1%

04. Charged detection time
This is the time the charged-parameters (Charged Voltage and Tail Current) must be met
in order to consider the battery fully charged.
Default Range Step size
3 minutes 1 – 50 minutes 1 minute


Hope this helps!

 

[capran]

I'll read that again a few dozen times and hope I can wrap my head around it. Since I am charging via motor, there is no float or bulk indicator. But it makes sense that running the motor 2.5 hours is not fully charging the battery , hence the fact that it says full 100% and the AH are zeroed out, it does not mean that it's fully charged. Especially given the fast reduction in volts over time.

 

[twistedtree]

I'd suggest getting a good hydrometer and checking the specific gravity in the battery cells. That is the definitive measure of charge state. You meter is only reliable once it have been calibrated and adjusted to your batteries. So start with specific gravity to determine the real state of charge, then adjust your meter/gauge so it reflects it correctly.


I think you will find that your batteries are not fully charged. Specific gravity should be 1.260 to 1.270. I don't recall the exact number, but check the Rolls documentation to confirm.

 

[PM]

The trouble with big batteries is just that, they are big, and heavy. Are you sure your amp gauge is accurate? Maybe check it with a good multi meter.

pete

 

[Bacchus]

Just a few comments and a worthwhile link on understanding, programming and using your Victron monitor.

https://marinehowto.com/programming-a-battery-monitor/

CM is a commercial member here on TF and a very respected resource.
The article is long and detailed but IMO worth multi reads to understand his points.

Just a few random thoughts based on my (limited) reading & understandings.

Accurate programming requires extensive testing of your actual battys characteristics and won't be (as)accurate if using mfg supplied specs

If battys are new they likely are not actually at the stated AH capacity. CM shows an example where it took hundreds of cycles to reach rated capacity.

Batty capacity is an ever changing target so the SOC % is the least accurate parameter displayed and accy will change over time unless periodic testing & reprogramming is done.

I have found that with my Balmar SmartGauge monitor my shore charger frequently switches to float before my bank reaches 100%. I need to cycle my doors charger off/on to initiate an additional bulk/ absorption cycle to get my batty bank close/to 100% SOC.

Charging from eng alt w/o external V regulator is an inefficient charger and getting above about 80% SOC takes a loooong time.

Trying to determine SOC based on V is very difficult while cruising as you never have battys w/o charge or load of some sort.

 

[capran]

I did check with my hydrometer when we got to the boat and every cell showed fully charged, but I hadn't thought of using that as an ongoing check. With my link 20 on my sailboat I found the battery monitor spot on. When we did a 4 hour run several days ago after 2 hours the meter zeroed out the amp hrs and was still charging 30 amps, leading me to think it is still accepting significant change. And it did sit for 2 days with higher volts remaining. Next time we sit 2 days I'll check with the hydrometer. Thanks.

 

[DavidM]

What kind of alternator do you have? If it is the OEM Lugger then it is likely to have a fixed voltage internal regulator. Balmar makes replacements that with their programmable external regulator will charge your batteries much faster.

If you do upgrade make sure to get the alternator case temperature probe. Those big batteries will pull a lot of amps over a long period if they start out depleted. The temp probe will cut back the current and keep the alternator from overheating.

David

 

[twistedtree]

I did check with my hydrometer when we got to the boat and every cell showed fully charged, but I hadn't thought of using that as an ongoing check. With my link 20 on my sailboat I found the battery monitor spot on. When we did a 4 hour run several days ago after 2 hours the meter zeroed out the amp hrs and was still charging 30 amps, leading me to think it is still accepting significant change. And it did sit for 2 days with higher volts remaining. Next time we sit 2 days I'll check with the hydrometer. Thanks.

Is it a hydrometer with actual numbers, or just a Good, OK, Bad scale of some sort. An SG of 1.265 stick in my mind for the Surrettes. It's also important to adjust for temp if not at 77F/25C.


I had a very similar issue with mine initially. They would go through what appeared to be a normal charge cycle, but just didn't have the expected capacity. This is when I discovered that although my charge cycle was according to their specs, the batteries actually need a LOT more charging. Their typical use is in applications where there is a 12+ hr charge cycle, if not longer. I was able to get the capacity back, but it took a huge amount of equalizing to de-sulfate them. We are talking about 20+ hrs of equalization, spaced out over days so I could monitor it.


Once I had them really back to full charge, I found that the only way to get them charged over the course of a daily solar cycle was with a really high bulk/absorb voltage. Same for a generator run which took 6-7 hrs.


The good news is that they did last 10 years, but in the last couple of years were consuming an enormous amount of water - like 12 gal every month or two. I also had two batteries fail. The first failed I think in year 1 or 2. It was replaced under warranty, but I had to pay shipping so it was very little actual savings over buying another battery. It was also weeks of back and forth with Surrette before they would accept that the battery was bad. Plus it took 2-3 months to get a replacement. This is the power system for my house, so it was a bit of a problem and I had to re-wire the battery bank for 44V and readjust all the charging to keep things going.


The second one failed in perhaps year 5 or 6 - don't recall exactly. This time I didn't bother with the warranty knowing it was useless because of shipping costs, so I just ordered a new one. But it still took months to get.



I'm sure they are good for certain applications, but an off-grid house is not one of them, even though they market to that application. I spent a huge premium on the batteries, and regretted it pretty shortly into my ownership.

 

[capran]

DavidM, On the alternator it says : Lecce Nelville model 8LHA207OVE 160 amps, sales no 110-555JHO Perstolqite Electric made in USA

 

[capran]

I'd suggest getting a good hydrometer and checking the specific gravity in the battery cells. That is the definitive measure of charge state. You meter is only reliable once it have been calibrated and adjusted to your batteries. So start with specific gravity to determine the real state of charge, then adjust your meter/gauge so it reflects it correctly.


I think you will find that your batteries are not fully charged. Specific gravity should be 1.260 to 1.270. I don't recall the exact number, but check the Rolls documentation to confirm.

can you recommend a specific hydrometer. The ones I got from Napa auto parts says low, good and excellent, with three numbers in each section- red, blue and green I think, like 1300 1275 1250; also, last night on the hook only 16 hours. the Ah had zeroed our when we arrived. this morning Ah read @-50, and Volts at 13.4. We only motored 2 hours each of the last three days. when we pulled into the slip and hooked to power a half hour later the charger lights went to float. If we motor 4 or more hours the voltage stays nearer to 12.5 after 24 hours. if we motor only 2 hours, we are into the 12.35V. I'm just used to the sailboat fridge that even after 48 hours was 12.4 v.

 

[twistedtree]

can you recommend a specific hydrometer. The ones I got from Napa auto parts says low, good and excellent, with three numbers in each section- red, blue and green I think, like 1300 1275 1250; also, last night on the hook only 16 hours. the Ah had zeroed our when we arrived. this morning Ah read @-50, and Volts at 13.4. We only motored 2 hours each of the last three days. when we pulled into the slip and hooked to power a half hour later the charger lights went to float. If we motor 4 or more hours the voltage stays nearer to 12.5 after 24 hours. if we motor only 2 hours, we are into the 12.35V. I'm just used to the sailboat fridge that even after 48 hours was 12.4 v.

The Napa device might be fine if there are gradations to read an actual number. Battery temp matters too. There are corrects to the SG reading for above/below 25.

 

[capran]

it just says Good 1300 1275 1250 then fair 1250 1225 then recharge 1200 1150 1125. bought it at Napa a few years ago. added water today (usually add and check every week. readings are 1275 and have tried turning off the charger and back on twice hoping it would stay at bulk or Absorbtion, but goes to float within a few minutes.

 

[twistedtree]

it just says Good 1300 1275 1250 then fair 1250 1225 then recharge 1200 1150 1125. bought it at Napa a few years ago. added water today (usually add and check every week. readings are 1275 and have tried turning off the charger and back on twice hoping it would stay at bulk or Absorbtion, but goes to float within a few minutes.

OK, at 1275 they are fully charged.


What is you steady current draw?

 

[capran]

OK, at 1275 they are fully charged.


What is you steady current draw?

I check the Ah on the BMV702 at 12 hour intervals. Here's a typical period. Motor to an island and anchor, arriving at 3pm. Batteries underway were charging about 30 Ah per hour. Battery monitor says 100% At 830 that night, , with no load, volts are 12.75, Ah is -21.7, 98.4% charge. (again, there are on the BMV702 which others are saying is not really an accurate measure, but that is the only device I have. at 830 am the next morning, voltage is 12.49. Ah cumulative since shut down used -35.8. 97.4%. motored to a new bay one hour away and anchor. 830 pm 12.48. -40.7 Ah used, 91.4%. If we sit 2 days, total Ah used from the time we anchor until the time we leave the morning of the 3rd day, was 132 Ah used, volts 12.27 and 90.2% showing on the monitor. Night time when cooler use less Ah, hot day time use more. fridge kicks on for 1 1/2 to 2 minutes and kicks off for the same amount of time. like I said, on my sailboat had 2 banks of two T 105's and with link 20 never went below 12.4 v, but the fridge was much smaller. looks like an average over night of 30 Ah and about 45 Ah during the day. My biggest concern was volts. sitting 36 hours getting into 12.35 range, and 48 hours 12.29volts.

 

[BruceK]

Are the 12.49, 12.35, and 12.29 voltages without any load actually drawing at the time?
Batts testing at 1275 seem good and likely not sulfated. Are all cells similar with minor variation?

 

[capran]

Are the 12.49, 12.35, and 12.29 voltages without any load actually drawing at the time?
Batts testing at 1275 seem good and likely not sulfated. Are all cells similar with minor variation?

Yes, I take a no load and a load reading. Very consistent difference. with no load, if it's 12.59, when the fridge kicks on it's 12.54. Batteries are brand new (2 months old). we pulled into a marina for a rare night as new friends visiting for a week. funny thing is, with the sail boat used to splurge and pull into a marina to charge everything up. seems like with the trawler, better to anchor out and charge via motor. not sure if previous owner hookd up BMV wrong. Underway, it charges and the Ah goes to zero after a few hours. where as with hooked to chore power the Ah does not go down as the amps are charged via the shore charger. ,makes no sense. currently the hydrometer saying 12.75, but at start of year all was reading 13.00 on the hydrometer.

 

[BruceK]

Doubt the difference between 1275 and 1300 matters but well done using a hydrometer. If the sailboat and the trawler had different brand batts that might explain the charging differences.
Is the shore charger showing a reducing charge despite the ammeter not changing? It does sound weird. Think you might be at the stage of getting an electrician onboard?
It`s good having a powerful alternator but I`d be a bit concerned if using the main engine as a generator to charge batts. They don`t like running long periods with no/little load, it risks glazing the bores.

 

[twistedtree]

Other than being different from your last boat, I'm not sure there is really anything wrong. But your meter installation is in question. The shore power charger should read on the meter, but it isn't. That suggests that the meter isn't installed correctly, and that other loads may not be read correctly.


You Ah consumption based on the meter is very low - almost too low to be believed which further calls into question the meter installation. You are using an average of about 2-3A. Perhaps other owners with boats in the 35-40' range could chime in with their typical at-anchor consumption? I might believe 2-3A average for a small fridge, and nothing else. But surely you use lights, have an anchor light, maybe a fan or two? Phones and laptop chargers? NMEA 2000 and other nav electronics that stay on?

 

[capran]

Other than being different from your last boat, I'm not sure there is really anything wrong. But your meter installation is in question. The shore power charger should read on the meter, but it isn't. That suggests that the meter isn't installed correctly, and that other loads may not be read correctly.


You Ah consumption based on the meter is very low - almost too low to be believed which further calls into question the meter installation. You are using an average of about 2-3A. Perhaps other owners with boats in the 35-40' range could chime in with their typical at-anchor consumption? I might believe 2-3A average for a small fridge, and nothing else. But surely you use lights, have an anchor light, maybe a fan or two? Phones and laptop chargers? NMEA 2000 and other nav electronics that stay on?

I agree that the install was not done correctly but hard to ferret out what to do about it. Will probably have to get an electrician aboard, but in our area it's over 200 an hour and a wait list to even get service. With the link 20 I hooked it up and it read incoming chare rates whether from running motor or at a marina. (last year in 2 1/2 months hooked up to shore power three times). we have LED cabin lights but use them maybe an hour or two a day max. Charge the phone when underway and maybe once when at anchor. no fan or other needs, as the pacific north west rarely hot. don't run our electronics/instruments except when moving.

 

[capran]

Doubt the difference between 1275 and 1300 matters but well done using a hydrometer. If the sailboat and the trawler had different brand batts that might explain the charging differences.
Is the shore charger showing a reducing charge despite the ammeter not changing? It does sound weird. Think you might be at the stage of getting an electrician onboard?
It`s good having a powerful alternator but I`d be a bit concerned if using the main engine as a generator to charge batts. They don`t like running long periods with no/little load, it risks glazing the bores.

Yes, different creatures and batteries, as well as charging, and large difference in fridge size. sailboat had a balmar 65 amp alternator with 2 banks of T105s for 210 Ah. the house has the Rolls 820 Ah charged by the 160amp alternator. I know switching from sail to trawler puts me over extended on the learning curve.

 

[twistedtree]

In the mean time, you could locate the shunt for the BMV and make certain that the "battery only" side is wired directly to the battery negative terminal with nothing else connected except the battery and the shunt.

 

[capran]

This might be helpful.
https://support.rollsbattery.com/en...ticles/10372-voltage-readings-state-of-charge

Sent from my moto g play (2021) using Trawler Forum mobile app

Thank you so much for the link. Have read it a few times now and maybe my expectations for voltage were too high. I had always had the belief that 12.1 was time to charge and that damage would result if less than 12.1V. Rolls is, on that table from your link, suggesting that 11.58 would be 50%. So far the lowest I have allowed it to go is 12.21, so maybe pushing it a bit more might increase the load capability. and no where near the number of charging cycles they suggest as needed to build full capacity.

 

[capran]

Are the 12.49, 12.35, and 12.29 voltages without any load actually drawing at the time?
Batts testing at 1275 seem good and likely not sulfated. Are all cells similar with minor variation?

yes. I do both load readings and no load (fridge running and not running). all cells with hydrometer very close to identical. I just replied to another post about the info from Rolls and suspect my expectation for higher voltage as well as lower drawdown might be in order. when I pull in to a dock (once each week to pick up and drop off company, the victron charger goes to float almost immediately even though I motored only 2 hours.