Need the solar/power pros to weigh in

TantoTrailers

Active member
I need to learn this whole multimeter thing...can someone point me in the right direction to start? I have the tools I'm just not sure what I am looking for...is it as simple as just checking and recording the battery Voltage at different times? Any 101 links I can look at? I would also like to run a capacity test on the battery once it is full like suggested but I also have no idea what I am doing there. I have a Renogy 100Ah@10hr battery: https://www.renogy.com/deep-cycle-agm-battery-12-volt-100ah/
 

shade

Well-known member
I need to learn this whole multimeter thing...can someone point me in the right direction to start? I have the tools I'm just not sure what I am looking for...is it as simple as just checking and recording the battery Voltage at different times? Any 101 links I can look at? I would also like to run a capacity test on the battery once it is full like suggested but I also have no idea what I am doing there. I have a Renogy 100Ah@10hr battery: https://www.renogy.com/deep-cycle-agm-battery-12-volt-100ah/
If you have a Victron BMV-712 on the way, you may as well wait until you have it installed.
 

luthj

Engineer In Residence
A battery's charge state can be measured at rest (not loads or sources) for 12 hours with a volt meter. Consult the MFG (or generic) VOC to SOC tables.

A capacity test requires a full charge. This means holding the absorb voltage for hours. In your case I would go for 12 hours or more, to recover from sulfation.

With a battery monitor you can just watch the return current. The BMV tracks AH in and AH out. However there is the "full charge" trigger. This is based on return current (charge current) and voltage. With the battery at the absorb voltage, the return current needs to drop below 2% of C (this is about 98-99%). 100% SOC is 1% of C in charge current. Many chargers drop to float early, and rely on the float to finish the last 2-3% of charge. The easy way to confirm a full charge with a volt meter only, is to check the voltage every hour or so, and record it. Note that many of your chargers may have a very short absorb timer, so you may need to manually restart the charge cycle to get enough absorb time to recovery from the likely sulfation of the battery.

You can also wire the multimeter in series with the charger, and set it to current mode. This will let you monitor the charge current, this can work if you don't have a battery monitor installed. Note that most multi-meters can only handle 10A max, so the charger needs to have started tapering before you do this.

As shade says, the BMV will make this an easy thing to monitor.
 

TantoTrailers

Active member
As I wait for the IP67 I'm trying to let the 3500 do its thing but I really cant tell what the hell its doing. Yesterday it got to the point of only the green light pulsing all others off and the voltage on my Renogy dropped to 13.6 at the battery. Today the 3 lights before the green are on, red and 2 yellows with the 2nd yellow now pulsing and no green. Renogy is showing 13.8...would really be nice to have some more visibility into the actual charger. Im glad I went with the Victron. Should have it late next week but I will be in Boston! Wont have a full charge till sometime before Halloween at this point. BMV arrives tomorrow so that will keep me busy.
 

TantoTrailers

Active member
For the BVM I need an accurate AH # so that means a capacity test. Is this easy enough to do? I'm not sure if it was mentioned before in this thread I feel like it has I just can't find it on my phone.
 

shade

Well-known member
Looks good to me. You may want to add some manual disconnect switches on the + side between the fuse block & battery, and the solar & battery. With those disconnected, you'll be able to isolate things for service. Make sure you have the best AGM profiles programmed into the charge sources, and let 'er rip.

If you have any concerns about the fuse block getting wet or damp, the Blue Sea SafetyHub series doesn't cost much more, and is designed for wet locations. It's also designed with low & high current sides, so there's some flexibility if you plan to run any high current loads and want to keep everything together.

You can also buy some of their fuse blocks with discrete sides, so some circuits can be isolated from those on the other side of the block. That can be handy if you want the capability to tie one side to a relay for ignition-on power, or something similar.
 
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TantoTrailers

Active member
The area this stuff is in is dry so I don’t have concern for water issues *knock on wood* I have a manual disconnect (power poles) at Rover for both battery and PV. I also have the inline fuse which is easy to pull which is what I do regularly to cut off the Fuse box. The switches I found were too bulky and I’ll post pics of exactly how little space I’m working in.

battery is now showing 14.4 at the Rover and I would like to do a capacity test to accurately configure the BVM. What’s the best way to do this without taking the battery into a shop?
 

luthj

Engineer In Residence
Use your amp meter to find a known load. Say 10A. An incandescent light bulb works. Measure the current, then you can remove the meter from the circuit if you like. Apply the load and start timing it. Once you hit 11V or so, it's done. Now recharge immediately. You have time and amps, do the math.

I would just wait until you get the BMV installed. Set up as approximately 100 amp hours to start. Then you can use the bmv to perform the load test . Simply disconnect all charging and apply a load such as a fridge lights etc. and wait for the battery to reach approximately 11 volts under load or 10.8 volts unloaded. The Bmv can show total AH removed. Usung this number, adjust the BMVs programmed capacity.
 

shade

Well-known member
I would just wait until you get the BMV installed.
LOL - Yep.

It sounds like the battery is back to 100% now, which it needed regardless of anything else.
With the BMV on the way, it makes sense to wait a few more days to get it calibrated to the battery.
 

TantoTrailers

Active member
The BVM has arrived today! But the charger is now on the way and I might as well wait for that to get it all wired in neatly the first time around! I need to stop adding things so I can just be done but nahhhhh. I will do the test when it’s all ready to roll!
 

luthj

Engineer In Residence
As an interesting aside, I made a mistake when I setup my solar charger (on my van) a few years ago. I set the charge termination too early, it should have been holding the absorb until sub 1% return current for my deep cycling application. Fast forward 2 years of full time off grid living, its winter in New Zealand, and I notice I am getting capacity drift. I discover my 500AH lead bank is badly sulfated, the sulfation made me think I was getting mostly charged, as the current would taper much earlier. Bad mojo. So I get a 15A shore power charger, and find a place to plug in for a couple days. I set the charger to ~15V (special recovery charge for my battery type). And let it run. After about 2 hours it tapered to under 5A, supposedly full. But after about 20 hours it actually rose again to 15, then slowly tapered down to 1A over the next 24 hours. I was able to get it back to "Full" but the capacity that was locked up in sulfate crystals was significant, and nothing short of a few months on a desulfator would free it up. Upon returning to the states I did a capacity test, about 65%. Total cycles was not even 300x50% equivalent.

What caused the capacity loss? Deficit cycling. Failing to get a true 100% charge every few days, or at least once a week. This adding/removing lead sulfate on top of the base layer causes hard crystals to form, sulfation.
 
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luthj

Engineer In Residence
Lead Acid batteries become Lazy when they are slowly discharged and then slowly charged back up.
Not really true. Lead doesn't have at true memory effect like NIMH or NICAD. Now the plates do have whats called porosity. This can influence how a battery performs under a large load (C/2 or greater). Low porosity will produce larger loaded voltage drop. Back when lead acid was used in DIY electric cars, it was well known that to get good performance at rates as high as C4, the charge rate needed by be C/2 or greater. Most AGM batteries need at least C/5 initial charge rate to ensure good porosity, and plate formation.

When a lead battery is discharge the active material is removed form the anode and deposited on the cathode. When its recharged, the anode is actually be rebuilt, and its physical structure is affected by the rate of recharge. Though lead tapers quickly, so the frist 15-30 minutes after a deep discharge are often best spent at whatever current the battery will accept (at absorb voltage).

There is some disagreement among experts, but some argue that a few modestly deep charge/discharge cycles at higher rates can help break up sulfation.


Here is some photos of lead acid plates in various stages of sulfation. Lead sulfate on the plate is generated whenever the battery is discharged. Normally its amorphous, which is a disordered mass on the molecular level. Over time crystals start to form. These are a structured/ordered lattice. The bonds in this lattice are very difficult to break, and normal charging will not cause the sulfate to dissolve into the electrolyte, where it can be returned to the anode. as lead oxide. The issue is that lead sulfate is not very soluble in strong sulfuric acid, so as the battery becomes more charged, the crystals have less incentive to break down, even at higher voltages. In flooded batteries, you can fill the battery with distilled water, and recharge to remove the sulfate. Then empty the battery and refill with normal sulfuric acid electrolyte. This can recover from modest to severe sulfation, though some capacity loss to exfoliation is to be expected.



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