12V Battery replacement with H4

[carys98]

BMS system generslly should not care about the battery capacity. Its only job is to get it to a full state of charge.

Agreed but if it doesn’t know the capacity it can‘t give you a percentage SOC. It will only be accurate at 100%.

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[Adventureboy]

I've always used voltage never soc when determining battery health.

Agree, voltage alone is way more useful than SOC alone, but they are related, and voltage is only meaningful if you know the SOC and the current draw at the point in time when you take the voltage reading.

• 12.7v doesn't tell you if it has the capacity to get through the day. This is why so many folks have batteries that test ok on inexpensive testers, but the truck still gives them messages every day. Replacing the battery solves the problem.
• 11.8v doesn't tell you if the battery is bad or just discharged to 30% SOC, or handling amperage for a dozen live modules with an update in progress. I've seen updates draw down to 11.0v on a healthy battery.
• 7v is probably pretty bad, although I've seen this a couple of years ago on the wife's MME on a fully discharged AGM (HVBJB failure). The battery recovered and is still operating 2 years later.

 

[Adventureboy]

Load test is the only way in my professional opinion, I've used one of these at home and the shop going past 40 years now.

Yep. Have one too. Useful piece of kit. Voltage under load.

 

[mr.Magoo]

I'm interested in what you've seen on this front.

This is pretty representative of what I see regularly.

While charging it's typically around 14.5 - 15V, once the battery is almost fully charged (+90% SoC) it goes into the "float" stage and the voltage is reduced to 13.5V.

 

[Adventureboy]

This is pretty representative of what I see regularly.

While charging it's typically around 14.5 - 15V, once the battery is almost fully charged (+90% SoC) it goes into the "float" stage and the voltage is reduced to 13.5V.

That's the proper way to charge an AGM. Mine is pegged at 15v measured at the battery posts. 7-hour HVB charge cycle a few days ago - 15v the whole time. Maybe this is why my Lightning is hard on LVBs.
What do you use to capture the data?

When you get a minute, can you tell me what your Battery Monitor Sensor part number is? I had mine replaced under the CSP, and have ML3T-10C652-BA. Perhaps it is simply a bad one or they replaced it with the wrong one.

 

[mr.Magoo]

What do you use to capture the data?

My own OBD based data logger

https://www.f150lightningforum.com/...g-flight-recorder-black-box.15411/post-493170

 

[Adventureboy]

My own OBD based data logger

https://www.f150lightningforum.com/...g-flight-recorder-black-box.15411/post-493170

That's quite a nice setup. Is your OBD polling set up through the Pi? I'm guessing you only log data while running, or did you solve the problem with OBD polling, activating the modules while OFF?

 

[mr.Magoo]

That's quite a nice setup. Is your OBD polling set up through the Pi? I'm guessing you only log data while running, or did you solve the problem with OBD polling, activating the modules while OFF?

Thanks !

Yes, I'm logging whenever the truck is on or charging (it's still kind of 'on" at that point so...).

The modules are sleeping when the truck is off so you won't get a reply from them and I've tried them all at this point hoping to find something useful. If you do poll the same module often enough, like 3-10 times within a few seconds (I forget the actual number, but it's something like that) it will actually wake up the modules and you can request data - but - it's not like the truck turned on, so you have no power supply (the DC/DC) so now you start to drain the LVB battery and it drains pretty fast - so in the end it's not really worth it.

 

[Kansan]

The Ancel monitor and all other 2-wire monitors, including my BM6, which is probably identical to Ancel anyway, will never be accurate for SOC. It will only be a calculated guess based on the average voltage over time and the ambient temperature. It doesn't have the amperage in/out needed for accurate SOC like the onboard BMS. Voltage, on the other hand, is quite accurate with the BM6.

My experience is that my BM6 always calculates SOC under the OBD2 BMS value on our Lightnings. This is probably because the small battery causes lower voltage with any loads applied compared to a normal-sized battery, for which it is probably calibrated. This morning, ODB2 reads 60%, and my BM6 reads 47%. I use SOC from the BM6 for trend analysis.

The BM300 is the one you want. Don’t need SOC from the Bluetooth monitor. The BM200 is only going to give accurate SOC when all the modules are fully shut down - no key fob nearby, no door opening for a half hour, ignition off for a half hour, etc.

I see you have a BT (Ancel?) battery monitor. I've had my Ancel BM200 for almost 3 weeks and it still gives extremely incorrect SOC readings compared with my OBD reader. Anyone else have that monitor behavior? Is mine malfunctioning or does it take a very long time to equilibrate?

That monitor can only give you an accurate SOC based on voltage. And it would need to be when all modules are completely off - so ignition off for a half hour, key fob out of range for a half hour, no doors opened for a half hour, etc. It's using voltage and a table of voltage to SOC.

 

[Airforce]

I don’t have any hard evidence but I don’t believe the BMS is only concerned with voltage. I believe it is a ”fuel gauge” type of BMS and is monitoring the current in and out of the battery. If it only cared about the voltage it would just connect to the positive lead and would not need to be in series with the current path. That is why it is important to always connect a charger downstream of the BMS. A voltage only BMS would not care where you connected.

Thinking about it some more it still probably doesn’t matter but the SOC number will probably be wrong. The BMS is calibrated to a full 35 Ah battery so if for example you have drawn 3.5 Ah from the H3 it will show 90%. If you have an H4 your actual SOC after drawing 3.5 Ah will be 93%. You will always read lower than your actual SOC which should actually help keep it charged.

Is a LVB Voltage Reading of 12.47 considered Normal on a truck sitting overnight?

 

[mr.Magoo]

Is a LVB Voltage Reading of 12.47 considered Normal on a truck sitting overnight?

Personally I'd say that's pretty normal.

Both my trucks LVB and my backup battery (also 30Ah AGM) are both at 12.5V right now and they've been sitting for about a day.

 

[carys98]

Is a LVB Voltage Reading of 12.47 considered Normal on a truck sitting overnight?

I’m not really an expert on this but I don’t really trust using the voltage to determine SOC. If you search around there are various sources and they don’t all agree but it looks like 12.47 is somewhere around 80-90% SOC. The other concern is that unless you disconnect the battery you don’t know if there is a load that might be dropping the voltage.

Here is one chart that I found.

 

[jwrezz]

Personally I'd say that's pretty normal.

Both my trucks LVB and my backup battery (also 30Ah AGM) are both at 12.5V right now and they've been sitting for about a day.

You have a backup battery? How is it wired and where do you keep it?

 

[Adventureboy]

I’m not really an expert on this but I don’t really trust using the voltage to determine SOC. If you search around there are various sources and they don’t all agree but it looks like 12.47 is somewhere around 80-90% SOC. The other concern is that unless you disconnect the battery you don’t know if there is a load that might be dropping the voltage.

Here is one chart that I found.

This chart would be fairly accurate if the battery were disconnected. The battery voltage will read lower for a given SOC while it is powering up modules, which is always the case if the frunk is open.

 

[Adventureboy]

@mr.Magoo when you get a minute, can you check what part number is on your Battery Management Sensor? I had the CSP done a while back, but the part number on mine is ML3T-10C652-BA and doesn't match the CSP. I think the part is just a dumb current shunt so it should be ok, but I'm concerned because my voltage at the battery post is high compared to what you are seeing.
Last night, my charge cycle was 2 hours and it held ~15.28v for the full 2 hours. Last weekend, my charge cycle was 7 hours and it started around 15.25 v and ended at 14.99v. Driving today ranged from 15.21-15.23v (on/off for about 2 hours)
Figured I'd verify the voltage, so I started the truck and it read 15.18v on the monitor, but only 15.0-15.05v on the CarScanner. I figured, ok, makes sense because there is probably a minor loss through the wires to the module if they are carrying the current to run the module and my monitor is measuring on the posts. Got the multi-meter out and it matched the monitor (actually read about 0.02v higher than the monitor, which is close enough). SOC was 83% on the ODB reading when I did this.

Interesting dynamics while doing this. Sitting in the seat, the voltage was over 15v frunk open. When I went to the frunk, the voltage dropped to just over 13v. Thought that was weird, so I went back and sat in the seat - it jumped back to 15v. Definitely have some complex algorithms going on here...

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