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Discussion Starter #1
Now that I have a battery monitor on my boat I am starting to collect information on my battery system. I have only had the monitor for a couple of weeks, and we have yet to spend any time off grid, but already I have noticed some interesting behavior. While the boat is at the dock it is on shore power, and the battery charger is always on. Even with the battery charger on the monitor indicates the batteries are slowly discharging. There are a couple of small parasitic loads on the system, mainly the electronic instrument panel, and the stereo system which is always powered so it maintains clock and radio presets. I would have thought that the battery charger would easily compensate for the small load, but after a week the monitor indicates the SOC is at 97%.

If I cycle the power off and on again on the battery charger it will ramp up it's output to top the batteries up, but eventually the monitor indicates a slow discharge again.

Is this behavior normal or is it an indication of a lower quality battery charger? The charger is a Cristec CPS2OEM 40a 3 bank unit. I have read that they are not the greatest charger. Should I be thinking about upgrading it? If so, who makes the best chargers?

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I have a Mastervolt charger 50 volt 3 bank for 8 years. Very happy with it
Only use 1 bank and echo charge the starting bank
6-6 volt AGM Lifelines at 720 ah. And blue top Optima starting AGM at 800 cc amp

No luck before that with Xantrex.
 

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While I dislike the Cristec chargers and have replaced all but one on my boat, I think that the problem isn't with the charger in this case. When in float mode the charger will maintain a fixed voltage and adjust the amps going into the battery bank to hold that voltage. My guess is that your voltage after a week is the same as it was the week before and the actual SoC is 100%.

Which monitor do you have aboard? It is possible that the settings, particularly those for the Peukert value, the charge efficiency, and the natural discharge values, are not optimized and this might lead to a slow deviation.
 

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How is your monitor determining SOC? Did you have to tell it the Amp Hour capacity and it's counting amps in and out? That method is often incorrect by a few percentage points. It can be incorrect by even more, if you press the set button claiming the bank is full, when it isn't.

The other possibility is the charger switches from absorb (higher voltage) to float (lower voltage), without the banks truly being ready for it. Therefore, the banks never truly get to full. If they are theoretically at 90%, but you tell a monitor they are at 100%, the amp counter just measures up and down from there.

The charger needs to hold Absorb, until a set amp acceptance, to charge fully. I have a feeling the Christec just flips over on a time basis.

Some chargers also go into energy saving mode, after being in float for X hours. This might account for why you are seeing net drain, which should never be the case, while plugged in. The charger comes back on, after bank voltage declines to a set value. The problem there is, if you weren't at true full to begin with, by the time float comes back on, it can't ever get you back to full. It needs to start over at Bulk-Absorb, but doesn't know to.

All learned the hard way...........
 

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Discussion Starter #5
I installed the Victron BMV712 monitor.

Even if the true SOC isn't correct it is the downward trend that has got my attention. It seems like the charger is shutting off completely and current flow shows -1.5a. I am guessing at some point the charger kicks in to top the batteries off again, but at what point is that supposed to happen?

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Did you already have a shunt, or did you install that for the monitor. You have to be 1000% sure that no loads are coming off the bank, without going through the shunt.

My bet is that the charger is going off, the batteries are dropping below the float level, but the charger comes back on in float and can't get them topped up again. It is, however, only an educated guess. A BTDT guess.
 

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All of the Cristecs that I have had on my boats were set CPS3 models and set up for fast charge, which I always changed back to normal charge. This mode might determine the float voltage which might explain the negative current despite being in float mode. I have the CPS3 manuals on my web pages if you don't have a manual handy. https://www.sv-zanshin.com/r/manuals/manuals.php
 

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Discussion Starter #8
Did you already have a shunt, or did you install that for the monitor. You have to be 1000% sure that no loads are coming off the bank, without going through the shunt.



My bet is that the charger is going off, the batteries are dropping below the float level, but the charger comes back on in float and can't get them topped up again. It is, however, only an educated guess. A BTDT guess.
Yes I installed the shunt that came with the Victron unit. It is right in the battery compartment, so it is impossible for any current to flow out of the bank without going through the shunt. That is why even the small parasitic loads are showing up on the BMS as negative current flow.

I will have to dig up a manual for my charger and see if there are any settings that are incorrect, but it seems to be pretty basic.



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I briefly read the Christec manual, which says it switches from Absorb to Float, when amp acceptance is 15% of the chargers rated capacity. I don't think that has anything to do with when a battery bank is ready to go to float.

My charger, for example, has a charge capacity of 100 amps. The level at which it should switch from Absorb to Float is 2 amps (0.5%c on a 400 Ahr bank).

I'm beginning to think my guess was the issue.
 

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Discussion Starter #10
I found that my charger was set for "Boost" mode, and I read in the manual that it is not recommended when the charger is on for long periods of time. I turned it off because our boat does spend long periods of time on the charger. I then found a different manual that doesn't say anything about not using boost mode for long term storage, indeed that manual recommends boost mode be used for "wintering". I'm a bit confused by this conflicting information!



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The battery charger should be keeping the batteries at 100% SOC with only small loads on the battery bank.

So either something is wrong with the charger, or the battery monitor.

A check of the battery voltage will sort out which device is to blame. The battery voltage should be above 13.2v (this is lowest storage charge setting of any of the battery chargers). If it is constantly above this voltage the batteries are maintaing 100% SOC and the battery monitor is supplying the wrong information. If it is below this voltage the battery charger is defective.
 

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While on shorepower my BM always sounds the batteries getting a low charging current while on float from the battery charger/solar
 

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While on shorepower my BM always sounds the batteries getting a low charging current while on float from the battery charger/solar
A low current into the batteries is fine.

Current flowing out of the batteries and therefore decreasing the SOC when the battery charger is connected and there is not a high load is not normal. It indicates a problem somewhere unless this is a brief event as the charger switches modes.
 

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I installed the Victron BMV712 monitor.

Even if the true SOC isn't correct it is the downward trend that has got my attention. It seems like the charger is shutting off completely and current flow shows -1.5a. I am guessing at some point the charger kicks in to top the batteries off again, but at what point is that supposed to happen?

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Can you post a photo of the physical bank wiring, including the shunt. While I am not a huge fan of the Cristec chargers, it should be holding the battery at 100% SoC. Also can you list the dip-switch settings?
 

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Discussion Starter #15
Can you post a photo of the physical bank wiring, including the shunt. While I am not a huge fan of the Cristec chargers, it should be holding the battery at 100% SoC. Also can you list the dip-switch settings?
Here is a screenshot of the battery monitor today. The boat has been plugged in for 10 days.

On the charger dipswitch 2 is on. I switched Boost mode off last week.


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I can't see all the batteries and cabling in the photo, but have some suspicions. What is the cable with the green shrink wrap? I'm wondering if the charger is properly connected to the opposite ends of the parallel bank.

Get rid of those Jeanneau plastic wing nuts. You can tell some are breaking already. You can use a pair of dikes to cut out the nut from inside and reuse that, if you like. btdt. For that matter, why add the automotive terminal clamps, when a threaded stud is available, right next to it. My guess is the OEM batteries did not have separate studs, which is what I recall was the case with the OEM gel batteries, from Jeanneau.
 

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EVERY DC NEGATIVE WIRE ON THE VESSEL MUST BE ON THE LOAD SIDE OF THE SHUNT

With that in mind, where is this wire going??



Also crossing unfused positive & negative wires like that can lead to a dead short and potentially a boat fire. Jumper cables should be as short as possible with a slight arc only to alleviate undue tension on the battery terminals.
 

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Discussion Starter #18
Shortening and tidying the interconnecting cables is on my "to do" list, but at this point I am waiting to see if I end up replacing the batteries first. I don't like how messy it looks, or how the cables cross over each other, but on the short term I am not too concerned about a short. The insulation on the cables is very heavy, and would take years to chaffe through. I have inspected them and they are in good condition.

The negative cable you point to I believe goes to either the engine battery or a negative bus bar on the other side of the boat...I will confirm exactly where it goes this afternoon.

The green heat shrink cable is a jumper I used to put the shunt into the circuit.



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If the green cable is essentially the take-off cable from the bank, through the shunt, it does not appear to be at the end of the bank (again, can't see all connections). Assuming charge comes back through this cable, same problem.
 

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Discussion Starter #20
If the green cable is essentially the take-off cable from the bank, through the shunt, it does not appear to be at the end of the bank (again, can't see all connections). Assuming charge comes back through this cable, same problem.
The shunt definitely sees current flow into and out of the bank. It looks confusing because whoever installed the bank didn't orient all the batteries the same way. I installed the shut on the negative that goes to the battery switches.

I did think it odd that they didn't take it off the same battery as the positive, but on a parallel circuit you should be able to connect anywhere on the negative side, unless I am missing something?

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