robbieg

S/S doesn't change the sensor. My 5.0 is not S/S and it has the sensor mounted on the negative post.

tvsjr

The LVD is on the technical power bus, to prevent dropping the voltage of the technical battery to a damaging level. When we're talking $500+ batteries, killing them isn't a great option.

The default values would only occur if both batteries are disconnected (dropping power to the BCM). Not when only one battery is removed. And, the system will function based on what it perceives to be the main battery's SOC value... whether the batteries are paralleled (engine running and sufficient alternator voltage) or not. It doesn't have any knowledge of the battery's parallel status.

If I used a diode isolator, where power couldn't flow from the technical battery back to the starting battery, you would be essentially correct - the second battery would be perceived as just a high-current load. But when they're actually being paralleled, it's just one big battery as long as the solenoid is engaged.

KG7BTU

I wanted to take a second to thank you guys and your discussions, this will be immensely helpful as a decide how to permanently connect my radio, especially this bit you said, the ISOpwr I have will help make my battery just look like a load.

I have a couple additional questions you may be knowledgeable about; since the car has an AGM battery, will using an SLA aux battery be a problem, and do you have a way to limit the current that will charge the aux battery? It is my understanding that it is bad to charge a battery with a lot of current, and I don't know how the system will react if the aux battery is drawn low and then the truck is turned on to start charging it.

Feathermerchant

As far as one big battery or two, the state of charge is calculated using the current sensor. So if it is only connected to the one battery then that is all the system will measure. If you want it to measure both as one, run both of the negative leads thru the sensor. Except is may not measure with the truck off.

However it does function with the truck off, doesn't it? It has to. That is one way it sheds load when the state of charge reaches some minimum.

Just watched this:
Check your battery voltage with your headlights on. It may raise it enough to charge the second battery.

stormsearch

What you have is a standard battery terminal with a Hall sensor, doughnut shaped wrapped around the battery negative cable very close to the battery B- post. If you ever see a BMS sensor on a S/S vehicle, would be able to see the difference. On F150's, only S/S vehicles has the battery negative mounted sensor.

To back this up, I'm the engineer at Ford who releases this part.

What I and you stated are the same thing. There are other implications which the BMS reset occurs, but I will only divulge information that is publicly available. I'm here as a die hard truck lover, but helping as much as I can.

robbieg

Oh ok, I assumed what I have on the negative side was what you were talking about. I have my BMS turned off anyways so it doesn't matter.

Feathermerchant

Stormsearch - So is there an easy way to achieve what we are looking to do?
ie have two batteries (starting and house) that can be separated so the house battery is discharged with the truck off then charged when the truck is restarted?

tvsjr

Definitely not worth losing a job over! My thinking is that, if I could figure out how to make the BMS kinda-sorta behave, it would be chasing its **** all the time trying to figure out what's going on. It seems to be a better and simpler solution to simply let it float whatever load is connected, just like the good ol' days... albeit it at a very minor MPG cost.

When start/stop becomes mandatory, this may become a much bigger challenge.

Exactly what I'm doing. Disable the BMS (via Forscan or by unplugging the sensor) and use a solenoid isolator (Blue Sea ML-ACR being a favorite). Or, use a diode isolator so the technical battery can't feed power back into the starting system, keep the BMS enabled, and ensure that the power being pulled by the technical battery flows through the BMS sensor.

Honestly, I think the ISOpwr is a kluge in this situation. There's nothing there to limit charge current, and the system is fused at 40A. On your starting system, you've got an alternator capable of 200A and a battery capable of several times that... even with a small battery, you have the chance of a problem, especially if you deep-discharge the technical battery. Something like the Blue Sea ML-ACR will handle 500A continuous and 2000A intermittent (assuming your wire can handle it as well), so you don't have to worry too much.

I don't like mixing battery chemistries, because the charging voltage differs. And, any battery other than fairly small SLAs has some form of vent and will out-gas if you charge it too hot. I personally choose either another automotive AGM (the Batteries Plus X2Power batteries being a nice choice right now) or one of the large Enersys Powersafe telecom batteries. No, neither is cheap.

Just my $.02. I have been accused of being a bit **** about this stuff. But, I have highly customized trucks on the road with 200K or more on the clock, still making emergency responses, without issues.

mjs3350

A lot of good info, here. Thanks Everyone!

TimelessR1

i know my trucks older...a 2010, but I'm running dual batteries, ones tucked up under frame rail in a drop down holder. I'm also using a Power Gate http://www.perfectswitch.com/isolato...fier-isolator/

to isolate the batteries...its def expensive...but have been using it for 3-4 years now.