Battery charger always on?

[JDCAVE]

After having enlarged lug holes for stud size on several occasions, there are good reasons not to do this, particularly with a battery bank. You want as much contact between lug and battery terminal to reduce voltage drop and to ensure your bank is balanced. When I replaced my T-105’s almost two years ago, I measured all cables and cross legs to ensure they were all the same length. I also replaced all lugs, downsizing them from 3/8” to 5/16”. Ultimately, I wanted all batteries to be contributing equally to electrical loads and similarly to be charging equally. To the extent possible the battery bank should be as balanced as practical. Also, you want batteries to “age” consistently, so that when it comes time to replace the bank, you are doing so because they are all equally aged.

Ultimately, lugs and ring terminals are cheap in the grand costs of boating and it doesn’t make sense to modify them to save a few cents.

I remember “CLectric” on this forum, in an earlier thread mentioning that it even matters whether a main carrying cable is above or below a cross leg. Subtle changes make a big difference. I kind of thought nothing of this until I tested it with a clamp metre and was surprised that it did make a difference.

Jim

 

[Bmarler]

While I am an advocate of using the right lug for the job, if the need arises to enlarge a hole I will. Those big lugs are usually all made from the same piece of copper, and the various hole sizes punched in. If a new battery needed a 3/8 hole instead of the 5/16 the old one had I would just open it up. Taking care to drill the right size and deburring the hole in the process.
I am interested in hearing the argument about the cable crossings making a difference on amp draw.

 

[JDCAVE]

I am interested in hearing the argument about the cable crossings making a difference on amp draw.

I had way too much time on my hands and I tried it out. I had gone through the trouble of balancing the amperage coming out of two boxes of 4 T-105’s each. Using a clamp meter, I measured the output of each box when the microwave was powered by the inverter. One box was contributing about 4 more amps to the load than the other box. By moving the supply cable above or below the stud on the bus bar made a difference on the relative contribution to the load. Similarly, whether the supply cable was above or below the cross legs made a difference. Not sure I know why but it did.

Edit: first photo. Positive bus bar with T-Fuse shown with cover removed.

Jim

 

[SteveK]

By moving the supply cable above or below the stud on the bus bar made a difference on the relative contribution to the load.

Jim, don't leave us hanging here. What was the difference? Is there then the better way to place cables, which on bottom which on top?
And we are accepting that there was absolutely nothing else drawing power from the 4A higher bank.

 

[JDCAVE]

Steve: I don't recall all the details. I'm sorry. BTW, with the exception of the "Digital Duo Charge" (which was not a draw on the bank during these tests), all house loads come from from the bus bar from where the two boxes connect. They are cabled as a single bank. I do remember the first attempt at measuring the output from the two battery boxes, one had about 10% higher amperage coming from it. So these were new batteries that hadn't been used during a cruising season. They had not been through any cycles. FLA's evidently take a few cycles to become most efficient so I wondered if perhaps there were subtle differences in the batteries. What I do remember was moving which cable was on top changed the amperage each box contributed to the overall load. I moved them about until they were nearly equal.

I have now been through 2 fairly extended cruising seasons so should perhaps try the tests again and report back. I'm back at home port and should go back and water the batteries and leaving them overnight before doing the tests.

I'm quite comfortable with my T-105 maintenance and how I have cabled the boxes. I think it was done with foresight and understanding. I go back to CLectric's advice on this on an earlier thread and while he might have sounded somewhat over cautious on the subject, my tests suggested he was correct. It matters whether the main cables are above or below the legs on the batteries when it comes to balancing the loads across the paired batteries and one is wise to test this if possible with a clamp meter with a new installation. At the end of the day, batteries are expensive and any low cost adjustments that can be made to extend their lives, ultimately pay off in the long run.

Jim

 

[SteveK]

Jim
Look forward to your new test. I have followed opposite ends for +/- and not at same end.
Over/under is now curiosity to check out.

 

[paulga]

I had way too much time on my hands and I tried it out. I had gone through the trouble of balancing the amperage coming out of two boxes of 4 T-105’s each. Using a clamp meter, I measured the output of each box when the microwave was powered by the inverter. One box was contributing about 4 more amps to the load than the other box. By moving the supply cable above or below the stud on the bus bar made a difference on the relative contribution to the load. Similarly, whether the supply cable was above or below the cross legs made a difference. Not sure I know why but it did.

Edit: first photo. Positive bus bar with T-Fuse shown with cover removed.

JimView attachment 157520View attachment 157521

have you considered adding parallel wiring at the mid point (Nigel Calder's 4th edition p125)? would this make any change in your test reading?

quote:
In a series/parallel setup, it is an excellent practice to cross connect the positives and negatives on the individual ...This minimizes differences in the way the batteries work and perform

 

[JDCAVE]

Hmm! That’s an interesting refinement. I’ll have to think about that.

Jim

 

[dhays]

I always liked this explanation and design. I think they may have taken it from another website that I can't find now.
How to connect multiple batteries

 

[paulga]

Measuring the collective is how it’s done. Like I mentioned earlier, after you install a battery monitor, you look at the usage to see what’s your normal behavior. That gives you a base line for voltage and amp draw or normal float amp draw on the charger. Then if something changes, you grab your multi meter and start investigating.

I installed the battery monitor near the portside battery bank according to my drawing in post 161. I had to cut out a corner of the battery container cover to fit the new cable. The third photo shows the aux wiring to the gen starter battery. The wisdom from you guys have allowed me to enjoy working in the engine room. Appreciate that.

@Bmarler this is the victron app interface. Which field is the normal float amp draw on the charger?

 

[Delta Riverat]

The wisdom from you guys have allowed me to enjoy working in the engine room. Appreciate that.

The most important things about working in the engine room are;
1) Turn on the blowers
2) Get a nice thick foam pad for under your butt

 

[paulga]

The most important things about working in the engine room are;
1) Turn on the blowers
2) Get a nice thick foam pad for under your butt

Thanks. Will try the blower next time.

 

[Bmarler]

You’re showing the history tab. What do we see on the status tab?

 

[paulga]

You’re showing the history tab. What do we see on the status tab?

This was the status on Sunday. The current "voltage" shows
13.22V. "current" has been 0 always. The battery selector is set to 1 which is the portside bank being monitored.

 

[Bmarler]

Ok, let me see if I can explain. The monitor is showing 0 amps as the charger is supplying the current to the house loads. There’s basically no current going into the batteries. If you look at the display on the charger you will see the amps going out to keep up with house loads.
If the battery bank has been discharged, when you turn the charger back on the Victron monitor will show amps going into the batteries. When off the charger you’ll see the discharge on the Victron monitor as well.
Float amps will have to be seen from the charger as it’s going to adjust output to maintain float voltage as needed.

 

[paulga]

Ok, let me see if I can explain. The monitor is showing 0 amps as the charger is supplying the current to the house loads. There’s basically no current going into the batteries. If you look at the display on the charger you will see the amps going out to keep up with house loads.
If the battery bank has been discharged, when you turn the charger back on the Victron monitor will show amps going into the batteries. When off the charger you’ll see the discharge on the Victron monitor as well.
Float amps will have to be seen from the charger as it’s going to adjust output to maintain float voltage as needed.

The battery capacity default value is 200ah, so it needs to be manually set. The battery bank is 3 NorthStar NSB-AGM31 in parallel, each has 103ah (manufacturer indicated c20 rate). So the capacity here should be set as 309? I tried other values but it didn't give any error messages

 

[Bmarler]

Yes, the 309 number is correct.

 

[paulga]

Yes, the 309 number is correct.

Thanks for the confirmation

 

[dhays]

Yes, the 309 number is correct.

309Ah would be correct for new batteries that actually meet their specs.

What about 5 years from now? We know that the Ah capacity of lead acid batteries does degrade over time and use. Should those amp hour figures be adjusted over time? Kind of like you might depreciate the value of your boat every year, might we not depreciate the Ah rating of our batteries every year? Ignorant mind is curious.

 

[Portage_Bay]

I always liked this explanation and design. I think they may have taken it from another website that I can't find now.
How to connect multiple batteries

Thank you for posting the link. I was aware of methods 1,2 & 3. Considered method 3 on my previous boat but could not make it work. Method 4 would have been possible.

 

[Bmarler]

309Ah would be correct for new batteries that actually meet their specs.

What about 5 years from now? We know that the Ah capacity of lead acid batteries does degrade over time and use. Should those amp hour figures be adjusted over time? Kind of like you might depreciate the value of your boat every year, might we not depreciate the Ah rating of our batteries every year? Ignorant mind is curious.

I wouldn’t change that number unless I did a controlled discharge to find the actual AH the bank will deliver.
We can all look at the amp draw and voltage to get an idea of whether or not the bank is performing well. We should also pay attention to our normal loads and voltage to get a baseline of what to expect. I look at my voltage, amp draw and soc every morning when I’m away from the dock. If anything seems abnormal I’ll give further scrutiny. If the bank seems like it’s not performing well, I’ll do a controlled discharge to confirm.