Battery monitor draw vs. long-term storage

[Sunbeam]

Hi folks,

I have a Victron BMV600S battery monitor wired into my boat, and have recently realized that I failed to consider something when I installed it. Hence I "get" to order a new house battery :cry So this thread is partly for discussion and partly to (I hope) save someone else from a similar fate (although maybe no-one else would be so stupid ).

When I hooked up the battery monitor, I did have some thoughts about long term slight load when in storage, but I guess I kind of shuffled them under my mental rug, partly because I wasn't sure what I might have to re-set after shutting it off, and I had a number of other (more appealing things) to be thinking about. I figured I'd figure it out later....

Silly thing is, I was very careful when I wired things up, to be sure to make it so that when I shut the battery switch off, things were OFF (except for bilge pumps ,and... battery monitor). I even re-wired the ACR to eliminate its parasitic load (that was an easy choice, because I always want it off when the battery switch is off). So, the only things that are "hot" on my boat, when the battery switch is off, are two bilge pumps, and the battery monitor.

Of course I let figuring out the battery monitor slide, and then put the boat in storage over the winter. Bonehead move. Then a couple of weeks ago I got a PM from someone asking how I had handled the positive supply wire (to the shunt) and the corresponding load when in long term storage. Erm... :sad

Noting that I had killed my battery (11.4v when picked up from storage... ouch), I decided I had better get to the bottom of this before putting in a new one. I searched the web a bit and while I found many discussions of battery monitors, I found no mention of this issue (maybe it is so simple that no discussion is necessary). So I called Victron North America to ask them a few questions:

1) If I disconnect the battery monitor during longer term storage, what do I lose? Some history, probably, but what about the basic settings? Do I have to do those again each time?

2) Do I just put a switch in the red power wire (small wire from shunt to positive power post)? Anything I need to know?

The fellow I spoke with (Rich Shea) wasn't completely sure about what would be lost or retained in memory. He is checking and will get back to me. He also mentioned that I could disconnect the cable (cat 5 type connector) from the back of the monitor face and that would do it. I don't want to do that ultimately, because I want a switch right by my main battery switch* but I would still like to know if disconnecting the monitor head by the cable is a viable option, for the record. I am not clear on this because there is a printed circuit board on the shunt as well, and wouldn't that draw power? So I added that third question to my follow-up e-mail to him. I will report back to this thread as I find the answers to my question.

In the meantime, I'd recommend not doing as I did. Worst part is, I should know better! I mean, I'm no electrician, but still. There is something ironically annoying about killing the house battery with the battery monitor :amgry

Sunbeam

*I want a "real" switch back by the main battery switch so that I can decide upon leaving the boat "Is this shorter term, or do I have a charging source while I am gone for longer term, so I just turn off the main battery switch; or is this longer term, "unpowered" storage so I want to turn off the Victron too?"

 

[Aurelia]

That is funny and I have pulled a few good ones as well. Recently sewing velcro on the wrong side of a curtain not one, but three times. I just had to quit for the day on that one.

I use a Victron 600 monitor but my storage is next to the house in a metal building and I am always connected to power so I haven't noticed the draw.

Any chance you could use a small solar panel in your storage location to mitigate the need for a switch at all? The 4mah draw is low enough that only longer term periods (maybe beyond a month?) are really worth thinking about. Even a cheap 5-10w panel could make the difference depending on the details. Where are you located? Out n about doesn't narrow it down much.

Greg

 

[Sunbeam]

That is a bit funny but I have pulled a few good ones as well.

I must get the Bonehead Move of the Day award :roll: But there is always tomorrow

I store the boat in varying places as I travel, so the situation is always slightly different and somewhat unpredictable. I do prefer to store the boat indoors (so generally, no solar). Sometimes I have access to shore power and sometimes not, depending on what is locally available. I actually could have hooked up my 800 mA Battery Tender where I had the boat this winter, but I have a (probably baseless) fear of leaving things like that hooked up and running while completely unattended.

I would like to get a full boat cover; in that case I might be able to store outdoors and just let a small solar panel peek out from under the cover. But I still want to provide a good option for "powerless" indoor storage for future reference. I really like to have the boat indoors/under a roof when in longer term storage.

Will be interesting to see what Victron say about settings. I hope I would not have to re-program everything, but the main thing is to know what will happen.

 

[Ray]

I don't think 11.4V on a conventional flooded battery in itself is reason for a NEW one.

11.4V should be easily recovered from by charging ---- without any near-term effects.

 

[Sunbeam]

I don't think 11.4V on a conventional flooded battery in itself is reason for a NEW one.

11.4V should be easily recovered from by charging ---- without any near-term effects.

Really? That would be good news. Not just the cost, but it's a pain to get my house battery in and out - not difficult, but just fiddly (clearance was so tight I had to tap for the hold downs, which I have to completely remove first, etc.*) One question I have though: You say "conventional flooded battery." My battery is lead acid, but it's AGM. I'm guessing "flooded" means the typical "old fashioned" wet cells that you add water to, etc. I don't have that. I'd probably better get out the fiddly tools and the checkbook, I suppose (?) Sigh!

Doubly annoying because the lithium batteries look super interesting, but maybe not quite ready for this "non early-adopter."

Sunbeam

*I may improve this by moving the house bank; details in the moving battery thread.

 

[Sunbeam]

Well, I got an e-mail from Rich at Victron (super fast service!) answering the questions. Here is what he had to say (in blue):

1) History

After the first power-up and set-up, the BMV stores system information, AND historical information in non-volatile memory, meaning, you only have to set-up the unit once even if you lose power to the device. The unit will need to be synchronized after re-power, though. This can be accomplished by recharging the batteries fully, or if you are sure the batteries are full, you can manually synch the unit by holding the + and - button at the same time for 3 seconds.

I take this to mean that the "This is what you should consider 100% SOC" is what he is talking about re-setting. That's not bad at all. I'm very glad to hear the rest is retained.

2) Power draw when in storage

The unit draws 4mA of current under normal conditions, but if alarm and alarm relay conditions are present, it will draw 15mA. So, with no charge source available, the monitor actually draws more current trying to alert you that the batteries are low!

3) Switching it off completely to avoid any power draw

For complete power down over long periods, the safest method is to remove the in-line fuse of the positive supply cable. This eliminates any draw from the panel OR the shunt pcb. The fuse is rated at 100mA, so a switch that could handle this modest current would be fine.

After my PS question wondering whether disconnecting at the display head could really work due to the circuit board on the shunt:

I included in original answer, but you are correct, the shunt pcb will draw a small current as well, so removing the in-line fuse is the best bet to stop all current draw.

So this means that just unplugging the display head with the Cat 5 cable will not do it; this makes sense.

4) Additional note
... as a Victron employee and battery-lover, I would have to recommend a small charger to maintain the batteries over the storage period. At the very least one rated to overcome the self-discharge of the batteries, if not to also power the BMV during that time.

I hear what he is saying and that is preferable, but not always possible in every storage location. I don't know how (or if) this would vary specifically with AGM batteries, as they are supposed to be very low self-discharge. I have looked that up in the past and got the feeling that 6 months would be no problem, provided they went into storage 100% charged (they did) and there were no loads (oops ). I did write him back to ask specifically about AGM's, since I had him on the horn and was thanking him for the prompt reply and good info anyway. Might as well get input from an expert. I'll post back what I hear.

Removing an inline fuse is slightly unappealing to me, so I think I will rig up a switch. But the fuse is accessible and will work, so it's an option.

 

[Ray]

Yes, AGM's are different. Flooded refers to the conventional car batteries you add water to.

"They" typically say the cells start dying at around 11.8-12.0 or less. However, your discharge rate at the time it got down that low was miniscule with just the battery monitor. Knowing JUST A LITTLE about battery chemistries, I'd venture to say that when "they" say the cells begin to be damaged, it is with much larger discharge currents.

If it were me, I'd charge that bad boy back up and do a load test - put a load equivalent to 0.2-0.5 times the battery's capacity (0.2-0.5C) rating and see how long it lasts to get down to a 50% discharge level, measuring the time and seeing how close it is to the actual rating.

Just a thought, anyway.

R

 

[ssobol]

This is very good information. I have a Victron 602S that I haven't installed yet and was wondering about the very same things.

Thanks for doing the legwork.

 

[thataway]

The safest practice is to disconnect all batteries, especially when in covered storage. This way you avoid any chance a rodent (or mammal) might chew thru the wiring and cause a short when you are not near the boat. If you must leave the bilge pump connected-then connect it directly to the battery, (with a fuse).

Yes most of these monitors draw a small amount of current. You can easily measure this with your digital volt meter.

Even the battery out a current load, will have self discharge. It is less with the AGM, than the lead acid battery. But that needs to be taken into account. I stored both the Road Trek and C Dory 22 in the desert, or in S. Calif for as much as 6 months to a year, and put a small solar panel to trickle charge the batteries.

Drawing any battery down to 11.4 volts is gong to damage it. There will be sulfating the plates in the discharged state. This may or may not be reversed with one of the pulse desulfators. It is worth recharging the battery--at 11.4 it may or may not take a charge. Sometimes you have to hit it with a high voltage first, and then go with a low charge rate.

 

[Sunbeam]

Ray,

Thanks for the information and the detailed "how to" for testing. I might as well. Nothing to lose and I'll learn a bit in the process (and maybe save $300 to boot). I have no desire to limp along with a damaged battery, but right now I have the time to check it out while I do some other projects.

ssobol: Glad this will help you out.

By the way, since I had the battery expert on the horn, I asked about his advice to always trickle charge, vis-a-vis AGM. Here is what he had to say:

Ok, if these are AGM, then self-discharge should only be in the 2%-per-month range, so fully charged batteries should be fine over the winter (with no loads attached of course)

Based on this, I should be fine "long storing" my boat (6 months or less, but probably usually more like 2-3) as long as the batteries are fully charged when I put it to bed, and no loads are on them (duh!). This is what I thought I knew from research but nice to have it confirmed. But I slipped up on the "no loads" part.

Sunbeam

PS: Just saw the addition from Thataway. Points taken. Luckily there have not been rodents where I have stored (I detest them), but there is always a chance. If only disconnecting could keep them out And it's true that I could have disconnected my bilge pumps (boat was indoors). I don't believe they came on at all but then they were not needed either. Actually, I could disconnect both them and the monitor by just taking the ring terminal off of the "always hot" power post, as those are the only three things on that. Everything else is switched.

Right now it's a real pain to take the ring terminals off the batteries themselves. I aim to change that (have some questions in another thread).

I will probably just get a new battery, but I'll at least "play around" with this one just to see what happens.

 

[Sunbeam]

A follow up note from "battery guy" at Victron:

If 11.4V is the lowest it has seen, that is not too bad. Standard "low battery" alarms start around 10.5V. A 12V battery is considered functionally dead at 9V.
At worst, the life span of the battery may have been shortened a bit, but in general 11.4V is a recoverable stage. Just charge it back up to full as soon as possible.
You could also put a small load on the battery to double-check it. If the voltage on the battery drops a good deal with just a small load, then that 11.4V is just a surface charge on the plates and there may be bigger issues with the battery. If the voltage holds up well, only dropping slowly as the load duration continues, then you are probably OK

Would it be okay to just hook up my 800mA "Battery Tender" smart charger? I am in no rush (working on other projects anyway, not using boat power system at all), so the slowness of its charging wouldn't bother me. Is there any reason I would need higher amperage charging for this particular instance?

 

[Ray]

Actually, I think the slower charge would be a good thing in this case. If there is any damage (which I doubt), a high charge rate might not be too good.

 

[Sunbeam]

Excellent, thanks. I'll put the Battery Tender on it and go about my business for now (boat projects, but not using boat power system) - then see how it fares. And no more leaving Victron connected for longer term storage!

 

[thataway]

Several points:
First the Vecton comment that a battery is dead at 10.5 needs some explanation. That is if a recently discharged battery is at 11.4 volts it is 80% discharged and at 10.5 it is 100% discharged.

If you go the the open circuit voltage it is a different story--and your battery is not recently discharged, but represents a chronic state in low open circuit voltage. During short discharge cycles there is less chance of sulphate crystals forming. During long discharge, then much more likely and more likely battery damage.

From Lifeline battery web site:

SOC (%) vs. OCV
the battery State Of Charge vs battery's Open Circuit Voltage

An easy method to estimate the State of Charge (SOC) of the battery is by measuring its Open Circuit Voltage (OCV). This measurement should be made after the battery has been at rest for a minimum of four hours with the battery shut off from its charging source and load. The voltage is listed as Volts/cell and for a 12V (6 cell) battery at 25°C (77°F).

State of Charge (%) OCV per 12V battery
100 ------------ 13.0 or greater
75 ------------- 12.6
50 ------------- 12.2
25-------------- 11.8
0------------ --- 11.4 or less

Can you recharge the battery with an 800 ma maintainer? Probably. What would be best for the battery? To get that voltage up as soon as you can, without overheating the battery, and put a desulphating unit on the battery. I would certainly try and save the battery, but I believe you only have one house battery. So thus you want to be fairly sure that it is in good shape by properly recharging and then testing.

My friends who work at West Marine many times bring home batteries which are traded back in, as "dead" and use them for years, after doing a proper charge and desulphation.

AGM self discharge is 1% to 3% depending on many conditions. These include amount of impurities in the lead of the plates, specific damage to the battery in the past, age,type of cycling in the past and elevated temperature. If you leave your boat in the desert--there will be more self discharge than in the frozen North. For example I have documented definite self discharge differences in Pensacola during the cold winter and the hot summer.

Tell me, how you know that where you stored the boat is rodent free? I wold love to know how to detect that. I do several things to prevent rodents, but I have never found a say to predict that there will not be an issue in any given storage area. Them rodents are everywhere!

 

[Sunbeam]

Can you recharge the battery with an 800 ma maintainer? Probably. What would be best for the battery? To get that voltage up as soon as you can, without overheating the battery, and put a desulphating unit on the battery.

Okay, I see. Unfortunately I don't have anything like that at the moment (actually I have to get the battery out of the boat and transported to where there is power before I can do anything). I do only have one house battery (although I'm thinking of going to two, but that's in another thread), so it needs to be totally reliable. Between that and not having proper charging equipment, I may just end up getting a new battery and chalking it up to a lesson learned. Also, if I do go to two, I don't think I'd want to pair a new one with this one, so there is that. I definitely don't want to do something like head out on Powell only to then find out no, the battery should not have been saved.

AGM self discharge is 1% to 3% depending on many conditions.

I did store the boat in the desert, actually, but then it was winter for the bulk of the time, so not super hot or super cold (why I chose it). I guess I won't know how it would have done just with self discharge this time since I "helped it along."

Tell me, how you know that where you stored the boat is rodent free?

I know because I stored it there for 7 months without the slightest sign of a rodent. I did ask before I brought it there, and they said they had no rodents, so I was hopeful but really? Not banking on it. I still "counted" on them trying to come in. Pleasant surprise is the folks were correct. Nary a turd, nor a whisker,. No sign whatsoever. I hate rodents so I was absolutely thrilled. The reason I made my comment -- it was actually a slight joke because you said something like "disconnecting the battery will keep rodents from gnawing through the wires," when of course you probably meant "will keep an electrical short or similar problem at bay if/when rodents do chew on the wires." I probably should just leave the attempts at humor out

Having lived in "winter" climates most of my life, I've had lots of experience with rodents (they like to come in for warmth and shelter in winter). Ugh!! Thankfully the boat is a bit easier to close up than an old cabin.

So... not sure what to do with the battery now, as I don't have proper equipment for charging it quickly, desulfating, etc. And I really don't want to spend an extended period of time "wondering" if it's going to be okay. I guess I'll start by researching the cost and storage size of a good charger.... can you suggest one that would do what I need?

Edited to add: I got the 800mA charger for a couple of reasons. One is that it was recommended here. Two is that it is physically very small, and I have a shortage of storage space. Three is that I was thinking I would probably add a "proper" charger to the boat, so wasn't really motivated to buy a really good/big charger for shoreside use as I thought it would sort of be a duplicate. Now however, I think I will probably not add a charger to the boat in the foreseeable future, so that changes things slightly.