That relay by the battery...

[JimD]

Instead of installing some new very heavy gauge cables that are hard to deal with due to stiffness, why not just piggy back another pair of 8 or 6 gauge wires along with the current wires?

Not sure if it holds true or not but 2 - 8 gauge wires in parallel would equate to a 4 gauge wire. Much easier to snake an 8 gauge wire versus a 4 gauge one. Cheaper too!

[craigav]

My plans (and recommendation here) would not really need to add more cable ampacity to the existing cabling. The dc2dc charger would limit the charge current to ~40amps and for a new and more powerful converter and inverter that would need a heavier cable for sure, but that would be a new cable directly between the converter\inverter to the batteries that I hope to keep short. That (more powerful converter\inverter) isn't really be required for my needs but it would provide faster recharge time and more inverter watts. Just having the higher capacity batteries is likely what most people are looking for, which in that case all that is needed would be the dc2dc charger and use the existing cables.

[Brian_HR]

Originally Posted by craigav

Not to overly concern you, I am not saying that with the amperage you reported that the cables are going to burn down and melt,

I did have visions of cables eventually melting due to being overloaded and risking a fire or something like that.

Originally Posted by craigav

For example, if you go to this website (or many similar ones) you can calculate the voltage drop.
https://www.calculator.net/voltage-d...s=40&x=54&y=20
Take for example the values I entered into the calculator. If you notice at the middle top area you will see that the "Voltage to the end:" = 13.25 for the parameters I entered.

This is a really handy website and I do have access to the terminals for the AC charger that the cable to the battery connect to so I'll confirm output at the charger is 14.6 and then measure what the voltage is at the battery and get the voltage drop. That will help confirm it is the cables and not something else wonky going on. Thanks for the recommendation.

Originally Posted by craigav

Do you have any more room nearby to the batteries? ~CA

The 24B has the AC charger at the back of the coach probably 15 feet from the entrance where the batteries are in the stairwell. There definitely isn't any room right next to the batteries in the stairwell but there is room in the kitchen cabinet area which is next to the stairwell. I was planning to use that area for the inventor I'd like to install but think I need to take care of the battery charging situation first.

[Brian_HR]

Originally Posted by JimD

Instead of installing some new very heavy gauge cables that are hard to deal with due to stiffness, why not just piggy back another pair of 8 or 6 gauge wires along with the current wires?

Not sure if it holds true or not but 2 - 8 gauge wires in parallel would equate to a 4 gauge wire. Much easier to snake an 8 gauge wire versus a 4 gauge one. Cheaper too!

Interesting you should mention that because I have two wires that attach to one terminal lug and I have confirmed that at least one of those wires is from the charger (no voltage on line and then voltage when ac charger kicks in). Maybe that is what Jayco did and used two wires to carry the current from the AC charger. I'm going to have to investigate some more when I get the RV back this weekend. I'll see if I can get a picture of that.

[craigav]

The dc2dc charger isn't very big, you may have room for it and the inverter, and unless you need to charge the lifepo4's up faster and need a larger converter\charger, otherwise you could simply keep the converter you have and keep things simple.

[Brian_HR]

Originally Posted by RPR

Attachment 68473

If I'm reading this graphic correctly that would mean if I have 45 amps coming off the ac charger and the run is 15 feet the recommended wire size would be in the range of 4 to 6 AWG, correct?

[craigav]

[QUOTE=Brian_HR;941901]I did have visions of cables eventually melting due to being overloaded and risking a fire or something like that.

I should probably elaborate just a little, your alternator is capable of 130a (at least that is common) and if you fully depleted your lifepo4 batteries and then started your engine, brought the rpm's up and started driving, in that case the lifepo4's battery voltage (and resistance) would be low enough even with the voltage drop to cause as much power as possible to transfer to your batteries from the alternator. This is the situation that could damage your alternator due to overheating and also could overload your wiring and they certainly could get dangerously hot, however on mine (and most) there is an 80a breaker on that line to prevent any more current than that which would limit any danger that even more current could cause (more than the 80a breaker). None of this is an issue though if you use a dc2dc charger as doing so limits the high current issues (cables, relays, alternator) and at the same time charges at the higher voltage that lifepo4 batteries need to have.

A point to add, sorry if being confusing a bit, the amps you reported are not an issue, the amps you could encounter with the lifepo4 batteries charging from the engine alternator certainly could become much higher than what you have already seen, and that will occur when those lifepo4 batteries are very low on charge, that is why I am saying things that sound contradictory.

~CA

[RPR]

Oxygen free copper cables, would they make enough difference in that they do not heat up as much?

[craigav]

This link matches the graph somewhat, the graph is good though, this is in a table format.

https://www.westmarine.com/WestAdvis...e-And-Ampacity

With this chart you can see that at 3% voltage drop you would want 6awg for your 45a at 15'. However, keep in mind that most converters (at least I have measured) don't put out exactly as much as they claim (but close). Also, off that converter you are powering other 12v things in the RV, so I would be very surprised if you had much more than 35a~40a going to the batteries from the converter anyway therefore, I wouldn't worry if you already have 8awg from the converter\charger to the batteries now, but if you installed a larger converter you would want heavier cables or move the converter closer to the batteries and keep the wiring you already have. ~CA

[houstonstroker]

I have a different brand of motorhome buy my solenoid just went out. It's a 300 amp continuous duty solenoid. Was not working correctly. Replace solenoid all is good except never knew how hot this guy gets. Rethinking my install and just ordered a BIM to replace my BIRD and Solenoid. I did cut open the old solenoid. The large copper disc has burn marks. The inside terminals were definitely covered in corrosion. It was a wonder it worked at all.

[Brian_HR]

Originally Posted by houstonstroker

I have a different brand of motorhome buy my solenoid just went out. It's a 300 amp continuous duty solenoid. Was not working correctly. Replace solenoid all is good except never knew how hot this guy gets. Rethinking my install and just ordered a BIM to replace my BIRD and Solenoid. I did cut open the old solenoid. The large copper disc has burn marks. The inside terminals were definitely covered in corrosion. It was a wonder it worked at all.

Where was the solenoid installed in your motorhome? Was it in the engine bay or some other location?

I believe in the Redhawk 24B the solenoid to connect the chassis and coach batteries is located in the stairwell next to the coach batteries. It's visible in the lower left hand side of the picture I posted on Post #43 in this thread.

[houstonstroker]

Originally Posted by Brian_HR

Where was the solenoid installed in your motorhome? Was it in the engine bay or some other location?

I believe in the Redhawk 24B the solenoid to connect the chassis and coach batteries is located in the stairwell next to the coach batteries. It's visible in the lower left hand side of the picture I posted on Post #43 in this thread.

I have the M2 chassis. The solenoid is located in first bay on drivers side with all other electronics.

[Brian_HR]

Originally Posted by craigav

Do you know what wire size you currently have? I suspect 8awg and with that you could simply go with a 40a dc2dc charger safely enough and not worry with changing any of the wiring. Also, I suspect the converter may be putting out closer to the 45 at the converter, just that it is not all making it to the batteries.

So, the cable from the charger to the batteries is actually x2 4 (four) AWG wires. The wire going to the generator is 2AWG and the negative from the battery box is also 2 AWG.

I also did some tests and drained the batteries a bit and drained and re-charged them. At a lower state of charge the shunt is showing more current and less voltage and as they charge the current goes down and the voltage goes up. I drained the batteries close to 75% and the initial current draw was about 40 amps and voltage at 13.56 voltage. By the time they were nearly 100% charged the voltage had risen to 14.3 and the current had dropped to 12 amps. That must be the battery BMS regulating the current, correct?

I'm curious to see the current draw then the batteries are closer to 20% charge and suspect it will be closer to the 45amps the charger is putting out minus the line loses.

[craigav]

Originally Posted by Brian_HR

So, the cable from the charger to the batteries is actually x2 4 (four) AWG wires. The wire going to the generator is 2AWG and the negative from the battery box is also 2 AWG.

I also did some tests and drained the batteries a bit and drained and re-charged them. At a lower state of charge the shunt is showing more current and less voltage and as they charge the current goes down and the voltage goes up. I drained the batteries close to 75% and the initial current draw was about 40 amps and voltage at 13.56 voltage. By the time they were nearly 100% charged the voltage had risen to 14.3 and the current had dropped to 12 amps. That must be the battery BMS regulating the current, correct?

I'm curious to see the current draw then the batteries are closer to 20% charge and suspect it will be closer to the 45amps the charger is putting out minus the line loses.

Hi Brian,

I am not sure what I was thinking earlier when I said I suspected you would have 8awg wiring to and from the batteries as I was thinking with a faulty processor at the time I suppose , all the schematics and even my rv which is older has 4awg to the engine alternator (via a relay) and either 4 or 6 awg going to the converter. (Which is good that the cable is larger than what I had stated earlier.) Your 2awg cable to the generator is to the generator starter motor, as the batteries still charge from the converter (or the engine).

With the larger cabling in mind, there is still an 80A breaker in line from the engine charge relay which could be exceeded (tripped) if the lifepo4 batteries were low and the engine alternator was running at the engine's higher than idle (normal cruising) RPM's. My alternator and I suspect yours as well as most are 130amp alternators. I would be more concerned with the alternator current than the converter current as if the alternator is charging all it can to the lifepo4 batteries along with some amps for the A/C blower fan, perhaps a few lights, then the alternator certainly would be running very hot (being that it would be close to 100% output for an extended period of time).

There are a couple of things that are working in your favor, however just not optimal for lifepo4 batteries in obtaining a 100% charge (not damaging though, just not a full charge) and that is that the charge parameters for the engine alternator regulator (and converter w/o modifications) continuously reduces the current as the battery gets into the low 14 volt range (the charge profile is a bit more complex but I am keeping it simple for discussions, the regulator takes into account temperatures and other factors). Usually when a certain threshold has been hit, say 14.3~14.8 then the regulators reduce the voltage down to the high 13's.

In any case, I think you would be just fine if you do nothing, however you could trip the 80a breaker and your alternator could get overly hot and have a shorter life, so I still recommend the dc2dc charger which does 2 important things, first is it limits the maximum current to what the dc2dc charger is designed for (40a with the one I purchased) which keeps the alternator from getting too hot, second important thing it does is change the charge profile to one that is optimal for your expensive lifepo4 batteries which is different than the lead acid battery charge profile your RV is setup for. A lead acid charge profile generally has 3 or 4 charge stages and a lifepo4 battery charge profile generally has 2 stage profile first being constant current (CC) until the battery hits the charger voltage set point commonly ~14.5v then switches over to constant voltage (CV) which reduces the current however much is needed to keep the voltage constant at the ~14.5 setpoint until the current is very low (<1amp common). That profile is what is needed to fully charge a lifepo4 battery.

If it were me, and it will be me as soon as I get around to it, I would check and see if your converter can be upgraded (if it doesn't already have the ability) to charge lifepo4 batteries optimally, and I would also add the dc2dc charger. Based on my wrong thoughts having 8awg wiring, you should be good with the 4awg wiring already in place.

Regarding BMS, interestingly enough, I have bought more than a few used lifepo4 batteries (for a very low price) and repaired the BMS inside. All the BMS does (which is very important) is balance the internal cells so that they are all equal, and the BMS limits (disconnects) the battery terminals if the battery voltage gets too low or too high. However those limits are more of a safety device for the battery as when the BMS disconnects the battery, the voltage is already too high or too low which you should never allow to happen. Also the BMS doesn't limit the current in or out (although I have replaced many internal fuses in lifepo4 batteries), (and many lifepo4 batteries have current limits one must be aware of or you risk damaging the BMS), so for all practical purposes, the bms is strictly used for balancing the internal cells of the battery and provides battery protection for very high or low voltages and is not a voltage or current regulator (which is why you want to charge your lifepo4 batteries with a charge profile optimal for them, they cost too much to invest in to not do so).

If nothing else, I would go with the dc2dc charger for the engine alt charging and leave the converter alone (if not easily switched to a lifepo4 charge profile) in doing just this you protect the alternator, charge the batteries to 100% while driving, however the converter will not fully charge them, but a lower than 100% charge is not really harmful and the next drive you take brings them back to 100%.

~CA

[Matrix]

Thank you. This thread has been tremendously valuable. I actually did a Google image search of the battery isolator solenoid in my 2015 Greyhawk 29me which directed me to this thread. I followed the instructions here and swapped out the solenoid and am now back in business! Alternator is now charging the house battery again! Saved a lot of money by doing it myself. Ain't the internet great!

[Kevin Cooper]

I put a shunt volt meter on my batteries in the negative connection side. It tells when being charged or used, amps, volts, watts, resistance of the battery, percentage of charge. I think it was $23 at Amazon.