question

fvjuke avatar image
fvjuke asked

Smart BMS 12/100 slow charge

Desperately needing help!

I have 2 Victron 330ah batteries charging via Smart BMS 12/100 with 80 amp fuse.

While driving or idle, I never get more than 40 amp charging (in the app, it says around 50% of alternator power) From my Promaster 2020 with 220 amp alternator. Never went higher,

Why don’t I see around 70 amp of charging?


I have seen a few posts with similar issues, but never a clear answer.

Thx, I really hope someone can point me in the right direction.

battery chargingBMS
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badwolf avatar image
badwolf answered ·

I ran into similar issues with my CL12/100. I have a Transit with Dual 250a. The CL12/100 is extremely sensitive to voltages.

In order to get 100% charge current, it seems to need at least 0.5v more on the alternator side when charging. (see attached photos) When the CL12/100 is charging it usually sees ~0.2v lower than my voltage meter on the starter battery. In the photos below my starter battery was showing 14.04v

If you are able to adjust your consistent alternator voltage, i found that above 14.4v is what the CL12/100 seems to want.

Also, only use the Victron Brand 32v mega fuses, its calibrated for them. I tried a few other 125a mega's and most were 10a less output.

screenshot-2024-07-04-233642.pngscreenshot-2024-07-04-233616.png


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screenshot-2024-07-04-233616.png (290.1 KiB)
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fvjuke avatar image fvjuke commented ·
So did you fix your issue? My MEGA fuse is from Victron. I am not sure how to adjust my consistent alternator voltage, but as you can see in the image I posted above, I usually get above 14.4v from the alternator charge according to the app.
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badwolf avatar image badwolf fvjuke commented ·

The photo you shared, the house battery should be at 100% or in absorption at 14.19v. So it shouldn't be a high current %. Also, at 6% current output you're not pulling any real power from the alternator, so it shouldn't drop the alternator voltage.

What is the CL12 showing for the alt/starter voltage when your house battery is below 13.3v?

My fix was a setting on the ford to get the voltage higher from the alternator, i don't know promasters so i can't help in that domain.

The CL12 isn't a B2B charger, the CL12 is a current limited pass through, which uses ~0.5v of the input voltage.

A B2B charger will have a 100% output with the input above 13.6v, since it can step up/increase the output voltage.

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fvjuke avatar image fvjuke badwolf commented ·
The picture I posted was when batteries were almost fully charged. My problem is that even when my SOC is at 80% and charge with alternator, it charges at 50 amps and I think it should be able to charge at 70-80 amp (with 100 amp MEGA fuse). When it charges at 50 amp, it says it uses around 50% of alternator charge. I will try to see what the alternator voltage charge is at next time I charge, I don’t know what it is. Since I also have solar connected, I had to set my batteries voltage charge to 13.9v and absorption voltage at 14.2v, like recommended by Victron. Don’t know if this has any implications with my alt charge issue…
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badwolf avatar image badwolf fvjuke commented ·
Again, the CL12 is very sensitive to voltage, when the mppt is charging its increasing the voltage of the house battery. You need the Battery Voltage and Alternator/Starter on the CL12 reading to be more than 0.5v apart.


One way you can lower the battery voltage to test the CL12 is put a large load on the battery with all other chargers turned off. AC, Microwave, Induction stove, should each be able to pull 1,000w/90amps. When i put a large load on my system my CL12 will jump to 100% no matter what the state of charge is.

You may want to check the data sheet on the batteries, the Charged voltage should be the Float voltage, all Victron batteries i've looked at the Float Voltage is only 13.5v.

LifePo4
Charging = Absorption
Charged = Float

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theo74 avatar image
theo74 answered ·

Some possibilities:

- There is a DC-DC booster installed in between the alternator and the smart BMS.

- The wiring between the alternator - BMS - battery is to thin, reducing the current.

- The charge current settings in the smart BMS need to be changed.

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fvjuke avatar image fvjuke commented ·
See my answers below
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fvjuke avatar image
fvjuke answered ·

Thx for your input

There is no DC to DC booster in between the alternator and the BMS, and the cable was able to charge at 80 amps before the BMS was installed.

I will post a picture of the BMS charge settings when I get home, but I believe it was at 14.2v.

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fvjuke avatar image
fvjuke answered ·

Ok, I can confirm:

- there are no DC-DC booster installed between the alternator and BMS

-the wiring coming from the alternator to the Smart BS is 4 awg size

-the charge current settings is set at 14.2v in the Smart BMS settings see picture below

What settings should be changed to what?

Any help would be appreciated :-)


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img-1884.pngimg-1874.pngImage Caption


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img-1884.png (157.8 KiB)
img-1875.png (250.5 KiB)
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pwfarnell avatar image
pwfarnell answered ·

So your images show that the alternator is at 14.43V and the battery is 14.19V measured at the BMS terminals. If you alternator would only supply 80A at 14.43V without the BMS, then adding the BMS will reduce the charge rate due to the extra resistance added to the charging circuit. You can not add resistance and expect the same performance. I suggest you try a larger control fuse because this will have a lower resistance and may help. Secondly, get your multimeter out when charging and measure the voltage drop from the stud on the alternator to the alternator stud on the BMS and from the battery stud on the BMS t the battery stud on the battery. If either of these shows any appreciable voltage drop then check the nuts are tight, the crimps are tight and consider larger cabling. On this type of circuit it is not the rating of the cable that is important, but the voltage drop and having larger cables will reduce voltage drop.

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fvjuke avatar image fvjuke commented ·
Ok, thx will give this a shot

I will relook at the terminals and screws and make sure everything is tight and try a 100 amp MEGA fuse.

These readings were when the battery was full.

When it is at say 80% SOC, it still does not charge at more than 45 amps. (With an 80 amp MEGA fuse)

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fvjuke avatar image fvjuke commented ·
Ok, I changed the MEGA fuse to a 100 amp and adjusted settings accordingly. I now get 50 amp of charge. At the start it will go to 56-57 and then drop down to 50 amp as if it adjusts itself. All the nuts on the Smart BMS have been tighten again. I also have 330W of solar panels on the roof which are always connected (but after the Smart BMS), not sure if this has anything to do with it. I have not been able to measure voltage drop yet, but will try soon. Any other advice would be appreciated.
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