4 Questions: 377 amp alternator charging LiPo system

mrfoamy

Mrfoamy
Soon I am taking delivery of a 2019 F350 with 377 amps output (twin alternators, twin batteries). I plan to connect a starter battery (with a PAC 500-amp isolator) to two 100 amp/hour Battleborn house batteries in my slide-in TC using 17 feet of 1/0 cable, and no B2B charger (since Battleborn says it may not be needed)…then check for overheating anywhere along this connection.

This might flow ~100 amps (fused 200) and charge two completely discharged LiPos in 3 hours. I assume the 7-wire harness that connects the truck to the camper (#10 wire) might also flow ~25 amps so charging flat batteries might be well under 3 hours. If anything gets too hot, I’ll install the B2B which will choke amperage to 60 amps and take longer.

Questions:
  1. Should I connect: only one starter battery to the isolator or one alternator to the isolator (as shown in PAC’s instructions)?…or both batteries, or both alternators? Continuous service of that load seems like a lot.
  2. Do I need to fuse the negative cable? I can’t see why. Both cables will run to an Anderson connector in the bed.
  3. Ideally an Upfitter switch will control the isolator but PAC does not specify a wire size or amp requirement. How small can this wire be and size fuse?
See if I’m thinking correctly:

I’m not bothering with solar or a generator since Ford is providing me with a free, convenient, fairly quiet, diesel 3,800 net-usable-watt generator with a 36 gallon fuel supply. Utilizing the high-idle option Ford provides (SEIC), just flip a switch (or dial a potentiometer) to raise the idle. Should be easy to wire the SEIC to an upfitter switch (with a potentiometer set to idle at the alternator sweet spot). Just not overly long with the diesel at high idle.

I expect there’s enough power for air conditioning and an induction range simultaneously, and still have juice left over to charge house batteries (assuming a big inverter and associated wiring)…Ok…don’t have those…Just saying.
 

Bayou Boy

Adventurer
You need to fuse both ends of the positive lead. You have two power sources and both need to be fused.
Use this Fuse block and related fuse. Very small, available in large current ratings, and high quality. Also, mounts directly to the battery posts.
Blue Sea MRBF Fuse

Also, you didn't say anything about an ACR in your post. You need something automatic that cuts off current when one set of batteries falls below 13v.
This one is rated for 120A continuous and 210A for 5 minutes.
https://www.bluesea.com/products/7615/ATD_Automatic_Timer_Disconnect

Blue Sea makes some that are rated up to 500A if you need that much. I don't think you will.
 
Last edited:

dwh

Tail-End Charlie
Depends on the alternator-battery wiring. If it's big enough, then just feed the relay off one battery.

But I'd bet a pair of BBs could absorb more than 100a. Running the 1/0 from both alternators to the relay would be optimal.

The power needed to energize the electromagnet in the relay is likely under one amp. Any old switch will do. It would normally be fed by an ignition hot to automatically engage when the engine is running. Putting it on a manual switch leaves you having to remember to turn it on (and off if the switch is fed by a contant hot).

The Blue Sea ACR is a great bit of kit. However the voltage setpoints for the auto connect/disconnect are all wrong for combining a Battle Born LiFePo4 and a lead-acid.
 

luthj

Adventurer
Battle born batteries have issues with continuous currents over 0.5C, I would size your wiring to restrict charging current to that level. This is due to the solid-state relay they use for the internal BMS. It has a fairly high resistance and suffers from spot heating under heavy loading or charging.
 
Last edited:

Bayou Boy

Adventurer
The Blue Sea ACR is a great bit of kit. However the voltage setpoints for the auto connect/disconnect are all wrong for combining a Battle Born LiFePo4 and a lead-acid.
That's where the ATD linked comes in. It only senses the lead-acid under the hood to switch voltage. It doesn't care what voltage the house battery is at.
 

john61ct

Adventurer
Battle born batteries have issues with continuous currents over 0.5C, I would size your wiring to restrict current to that level. This is due to the solid-state relay they use for the internal BMS. It has a fairly high resistance and suffers from spot heating under heavy loading or charging.
I've come across this a few times, and to me translates to reinforcing "don't use drop-ins".

Can you point to first-hand threads where this is credibly documented?

Or does BB actually admit to that limitation?

Finally, advising using wiring gauge to limit current is generally dangerous. That's what fuses are for.
 

john61ct

Adventurer
OP, if you want a bank that will really absorb 200+ amps, say 400Ah in a 2-hour trip, LFP is your chemistry, but a truly safe and effective implementation will cost many thousands of dollars.

The pragmatic approach to save some of that investment would be to first test your alt setup and determine whether or not it can **realistically** produce that kind of output continuously (for hours) under high temp end of your operating conditions.

If the true output is more like say 125A, then you can save a lot of up-front capital.

Of course all this begs the question, do you really **need** such a high rate?
 

Rando

Explorer
That's where the ATD linked comes in. It only senses the lead-acid under the hood to switch voltage. It doesn't care what voltage the house battery is at.
That doesn't quite work - when the batteries are linked, the voltage on both sides of the relay will be equal to the lithium house bank, and it won't disconnect regardless of which side it is sensing. It will connect when you are charging, then stay linked until the lithium is pretty much flat (below 13V). I have this issue with my ACR and lithium set up, but my wiring between camper and truck is pretty small, so it will disconnect if I load the lithium heavily.

You could wire this an ignition controlled relay, but at that point there are probably better options.
 

Bayou Boy

Adventurer
That doesn't quite work - when the batteries are linked, the voltage on both sides of the relay will be equal to the lithium house bank, and it won't disconnect regardless of which side it is sensing. It will connect when you are charging, then stay linked until the lithium is pretty much flat (below 13V). I have this issue with my ACR and lithium set up, but my wiring between camper and truck is pretty small, so it will disconnect if I load the lithium heavily.

You could wire this an ignition controlled relay, but at that point there are probably better options.
Have you used the ATD? It is single sensing and has specific posts for the charge battery and the house battery. It only monitors the voltage of the starting battery. It is designed for house banks that hold voltage longer than normal. Look over the link I posted.

On most ACRs the posts are interchangeable. They are not on the ATD.
 

Rando

Explorer
I've come across this a few times, and to me translates to reinforcing "don't use drop-ins".

Can you point to first-hand threads where this is credibly documented?

Or does BB actually admit to that limitation?

Finally, advising using wiring gauge to limit current is generally dangerous. That's what fuses are for.
BB recomends a charge rate of 0.5C (or 50A) in their documentation. Unfortunately they don't really provide true spec sheets for their batteries so it is hard to find these details.

Using wire gauge to limit current in this case is totally fine, and has nothing to do with fusing. Ideally you want to charge your lithiums to about 13.6 - 13.8V to limit balance issues, but the battery will essentially stop charging at 13.4V. Say you want to limit that charge current to 50A (for a BB) and your alternator is set for 14V you would design the wires such that at 50A the voltage drop is ~0.5V (so 10mOhms or 15' of 0 AWG), which would drop the voltage at the batteries to 13.5V and reduce the charging current.

Fuses are to protect the wiring, and we are no where near the carrying capacity of the wire here. This is happening whether you design for it or not, and is why you really don't need a DC-DC charger for lithiums, unless your wire is too thin.
 

Rando

Explorer
Have you used the ATD? It is single sensing and has specific posts for the charge battery and the house battery. It only monitors the voltage of the starting battery. It is designed for house banks that hold voltage longer than normal. Look over the link I posted.

On most ACRs the posts are interchangeable. They are not on the ATD.
No I have not used an ATD, but I have used a single sensing ACR (the older ones were pretty much all single sensing).

The single sensing only comes in to play when the relay is open, and the two sides can be at different voltages, and you can trigger to close the relay when one voltage exceeds a threshold. Once the relay closes, the voltages on both sides of the relay are the same, right? So at that point it doesn't matter which side it is sensing, it will stay connected until the voltage of both batteries goes below the disconnect threshold.
 

Bayou Boy

Adventurer
No I have not used an ATD, but I have used a single sensing ACR (the older ones were pretty much all single sensing).

The single sensing only comes in to play when the relay is open, and the two sides can be at different voltages, and you can trigger to close the relay when one voltage exceeds a threshold. Once the relay closes, the voltages on both sides of the relay are the same, right? So at that point it doesn't matter which side it is sensing, it will stay connected until the voltage of both batteries goes below the disconnect threshold.
Blue Sea makes ultra high quality stuff that does what it says it does. I'd trust their engineers rather than random assumptions. Regardless, a quick call or email to them will tell the original poster for sure. In all situations, I'd rather use something from them than something from some new-on-the-block overlanding electronics company if it will do the job.
 

Rando

Explorer
Blue Sea makes ultra high quality stuff that does what it says it does. I'd trust their engineers rather than random assumptions. Regardless, a quick call or email to them will tell the original poster for sure. In all situations, I'd rather use something from them than something from some new-on-the-block overlanding electronics company if it will do the job.
No argument here - it is likely a high quality device and does what it says it does. You just have to think about that that means for a particular application. In this case I think an ignition controlled relay is the best choice.

As I mentioned I have run into this issue with my lithium house bank, so I speak from experience. For me an ignition controlled relay doesn't work as I have solar on the camper and I want it to keep the truck battery charged when it is sitting in the driveway. I am still searching for a solution.
 

Bayou Boy

Adventurer
No argument here - it is likely a high quality device and does what it says it does. You just have to think about that that means for a particular application. In this case I think an ignition controlled relay is the best choice.

As I mentioned I have run into this issue with my lithium house bank, so I speak from experience. For me an ignition controlled relay doesn't work as I have solar on the camper and I want it to keep the truck battery charged when it is sitting in the driveway. I am still searching for a solution.
Could you use an "ignition controlled" relay and hook the lead to the terminal on your solar charge controller that connects to the panel? That way when the relay got 12v from the panel when the sun was up it would connect the banks. When the sun went down the voltage would drop and it would disconnect them.
 

Rando

Explorer
That is an interesting thought, but may have issues as the panel voltage can go up to 22V, and ideally it would also sense the alternator side as well. Really what we need is an ACR with programmable set points, preferably individually adjustable for each side and an ignition trigger. There are some products that are close, but nothing that is quite right.
 
Top