Adding second battery for winch in parallel - 6.6 gas

[hsfdchief200]

I have a Warn 16.5ti-s winch that I'm installing on our fire dept's 2023 3500HD with the 6.6 gas.  The winch can draw up to a max of 507 amps, per Warn.  This truck came with the snow plow prep package, so it already has the 220 amp alternator but only a single battery.  I came across some older posts about adding a second battery that was isolated, but I haven't found an answer on my scenario.

 

My preference is not to have the second battery isolated but instead have it wired in parallel like I understand the diesels to be.  Is there a problem wiring this in parallel and simply running positive to positive and negative to negative between the two batteries?  If it's ok to do, what gauge cable should I use?  The winch has 2 gauge cable going to it. 

 

The truck will also have a 2 gauge cable running back to a junction block on the flatbed to power the electric starter on the pump's Honda engine and for the electric rewind motor for the hose reel (50A fuse for that motor).

 

My main reason for not really wanting them isolated is so that the ever-rotating crews of people to use the truck will know for sure if one or both batteries start getting low if wired in parallel, as starting will become apparently weaker.  But if they are isolated, that auxiliary winch battery could be getting low without anyone realizing it, and I don't want to be in a situation of needing the winch and having a dead or near-dead auxiliary battery.  NOTE:  As bad as it is, I have to engineer for the lowest common denominator.  I had even thought about a dual battery voltmeter installed in the cab, but that wouldn't get monitored (and most of the guys coming through nowadays have very little mechanical knowledge as it relates to vehicles, so it wouldn't mean anything to them).  So I want as simple of a setup as can be safely done.

 

So I guess my questions are:

-Can a parallel dual battery install be done on this gas truck for a winch install? (I realize I need 2 new equal batteries to install at the same time - that's no issue)

-What gauge battery cable to run between the batteries?

-Should the winch be connected to the main battery or the second one (or does it even matter being in parallel)?

-Is there anything else to be done to the wiring to prevent any overcurrent or overcharging issues?  

  

[rjgvt]

I thought the aux battery was isolated when the truck was off and connected in parallel when the truck was running so it can charge. I’ll check my batteries tomorrow with the truck off and on.

[Another JR]

On 2/12/2024 at 6:42 PM, rjgvt said:

I thought the aux battery was isolated when the truck was off and connected in parallel when the truck was running so it can charge. I’ll check my batteries tomorrow with the truck off and on.

You are correct about the OEM aux battery arrangement on the gas trucks. I think the OP knows the OEM aux battery arrangement, but wants to do a simple parallel battery arrangement to deliver high current to the winch. 

Edited February 14 by Another JR

[Another JR]

1 minute ago, Another JR said:

Edited February 14 by Another JR

[Another JR]

On 2/12/2024 at 5:21 PM, hsfdchief200 said:

…

 

So I guess my questions are:

-Can a parallel dual battery install be done on this gas truck for a winch install? (I realize I need 2 new equal batteries to install at the same time - that's no issue)

-What gauge battery cable to run between the batteries?

-Should the winch be connected to the main battery or the second one (or does it even matter being in parallel)?

-Is there anything else to be done to the wiring to prevent any overcurrent or overcharging issues?  

  

I can answer some of your questions:

 

Yes you can do a parallel battery installation. There should not be any charging issues - when charging it’s the same as an aux battery with the isolator closed. 

 

I don’t know what size wire to recommend, but you could do the same size as is used on the diesel version, which has a plain parallel setup. 

Connect the winch to the main battery. You want the shortest path for the current from the alternator to the winch, and you don’t want to have to size the second battery’s wires for the battery current plus the alternator current when winching. 
 

Ideally you want appropriately sized fuses on the positive wire that runs between the batteries at each of the two batteries in case you have a short to ground in that wire. The main battery fuse block may already have an appropriately sized unused fuse. Mine (2021 gas with 220 amp alternator and aux battery) has an unused 250 amp fused connection.  Again, look to the diesel’s wiring for fuse and wire sizing clues. 
 

 

Edited February 14 by Another JR

[gemarsh]

I'm surprised at the small gauge wire. 2ga is rated at 65amps at 12v.

 

My calculations say you need 3/0ga for 12v, 500amp, 5% volt drop at a 6 foot length.

 

ETA...this is for copper, not CCA.

Edited February 14 by gemarsh

[hsfdchief200]

9 hours ago, Another JR said:

I think the OP knows the OEM aux battery arrangement, but wants to do a simple parallel battery arrangement to deliver high current to the winch. 

That is correct.

[hsfdchief200]

9 hours ago, Another JR said:

I can answer some of your questions:

 

Yes you can do a parallel battery installation. There should not be any charging issues - when charging it’s the same as an aux battery with the isolator closed. 

 

I don’t know what size wire to recommend, but you could do the same size as is used on the diesel version, which has a plain parallel setup. 

Connect the winch to the main battery. You want the shortest path for the current from the alternator to the winch, and you don’t want to have to size the second battery’s wires for the battery current plus the alternator current when winching. 
 

Ideally you want appropriately sized fuses on the positive wire that runs between the batteries at each of the two batteries in case you have a short to ground in that wire. The main battery fuse block may already have an appropriately sized unused fuse. Mine (2021 gas with 220 amp alternator and aux battery) has an unused 250 amp fused connection.  Again, look to the diesel’s wiring for fuse and wire sizing clues. 
 

 

Do you know what size wire and fuse the diesels use for that run between the batteries or where I could look to find that info?  I don't know of anyone in my immediate circle who has this version truck with a diesel.

 

I just checked the fuse block on top of the main battery.  There are no unused fuses.  It has a 250 which goes to the alternator, a 175 which goes to the fuse block on the driver's side, a 400 which goes to the starter, and two 60s which have wires going into a harness below the battery.

[hsfdchief200]

24 minutes ago, gemarsh said:

I'm surprised at the small gauge wire. 2ga is rated at 65amps at 12v.

 

My calculations say you need 3/0ga for 12v, 500amp, 5% volt drop at a 6 foot length.

 

ETA...this is for copper, not CCA.

2 gauge battery cable is rated for more than 65 (210 outside engine comp, 178 in engine comp per one vendor I've been working with), but it definitely isn't rated for the high max current this winch could draw at full load.  That was also surprising to me when I unboxed it, but it's hardwired this way straight from Warn.  They also say to wire it directly to the battery with no fuse or switch, which goes against every fiber of my being, but that's a whole separate topic.  I guess how they get away with the 2 gauge is the short run and limited run time of the high amperage.  Wiringproducts.com shows a 2 gauge battery cable capable of 300A for a 4.9 ft. run with 2% voltage drop.  

[hsfdchief200]

I looked back in the upfitter guide and found diagrams, but they don't show the wire size (at least that I can find).  

 

Could I simply order the main battery cable for the diesel and use it for the run between the two?  I found the part for a diesel, dual batteries, single alternator - 84906880 ( 2020-2023 GM Battery Positive Cable 84906880 | GMPartsDirect.com ).  It looks like it connects at the driver's side battery, has a small pigtail to connect to the driver's side junction block, then a long run to route over the firewall and connect to the passenger side battery.  Would it be feasible to just install this?

[Another JR]

3 hours ago, hsfdchief200 said:

Do you know what size wire and fuse the diesels use for that run between the batteries or where I could look to find that info?  I don't know of anyone in my immediate circle who has this version truck with a diesel.

 

I just checked the fuse block on top of the main battery.  There are no unused fuses.  It has a 250 which goes to the alternator, a 175 which goes to the fuse block on the driver's side, a 400 which goes to the starter, and two 60s which have wires going into a harness below the battery.

I don’t know the wire size or I would have posted it, but my neighbor has a 2021 3500 diesel dually. He might have the dual alternator setup but I don’t think that would make a difference. I’ll try to catch him today and see if I can tell the gage and fuse sizes. He won’t want me to disturb anything, so I may only be able measure wire conductor diameter rather than read the gage off the insulation. That should get you there, though. 

[Another JR]

7 hours ago, hsfdchief200 said:

Do you know what size wire and fuse the diesels use for that run between the batteries or where I could look to find that info?  I don't know of anyone in my immediate circle who has this version truck with a diesel.

 

I just checked the fuse block on top of the main battery.  There are no unused fuses.  It has a 250 which goes to the alternator, a 175 which goes to the fuse block on the driver's side, a 400 which goes to the starter, and two 60s which have wires going into a harness below the battery.

I was able to catch my neighbor just now and look at his truck. The wires themselves were completely closed up so I could not read wire gage or measure conductor diameter. FYI he has dual alternators. The 220 amp alternator connects to the main battery (passenger side) with a 250 amp fuse. The 170 amp alternator connects to the second battery with a 175 amp fuse.
 

The fuses at each battery block for the battery connection wire were 400 amp fuses. If you size your wire for a peak 30 second current of 400 amps and a long term steady state current of at least 200 amps I suspect you will be fine.  The part number of the cross battery wire is 84906880, which might allow you to find the gage, same part number as you posted above. It runs along the top of the firewall. It would have the angled crimp connectors used with the battery blocks. If you don’t want to buy a battery block for the second battery you’ll end up altering the wire assembly anyway for whatever connection you use, in which case I’d suggest making your own if you have a crimper, or have a local mechanic make you a cable. 
 

I have attached pictures of his battery blocks. 

[hsfdchief200]

On 2/14/2024 at 3:39 PM, Another JR said:

I was able to catch my neighbor just now and look at his truck. The wires themselves were completely closed up so I could not read wire gage or measure conductor diameter. FYI he has dual alternators. The 220 amp alternator connects to the main battery (passenger side) with a 250 amp fuse. The 170 amp alternator connects to the second battery with a 175 amp fuse.
 

The fuses at each battery block for the battery connection wire were 400 amp fuses. If you size your wire for a peak 30 second current of 400 amps and a long term steady state current of at least 200 amps I suspect you will be fine.  The part number of the cross battery wire is 84906880, which might allow you to find the gage, same part number as you posted above. It runs along the top of the firewall. It would have the angled crimp connectors used with the battery blocks. If you don’t want to buy a battery block for the second battery you’ll end up altering the wire assembly anyway for whatever connection you use, in which case I’d suggest making your own if you have a crimper, or have a local mechanic make you a cable. 
 

I have attached pictures of his battery blocks. 

 

Thank you so much for the info and pictures!

 

Getting the 84906880 harness and auxiliary battery fuse block would definitely be the easiest and cleanest method to do this.  I guess my only remaining question is the underhood junction/fuse block (X50A on the diagrams) that's on the driver's side right beside the spot where an auxiliary battery goes.  Currently, in the single battery gas setup, there is a wire running from the battery on the passenger side around the firewall to this junction block.  It's fused on top of the battery at 175A.  It only goes to this junction block and doesn't have any other branches from the harness.    From everything I can tell from parts pictures, the 84906880 replaces this wire with these differences:  it's fused at the main battery at 400A, fused at the other end at the auxiliary battery at 400A, and has a short dog leg coming off the auxiliary cable terminal to loop over to this junction block.  With the 400A fuses on both end of the 84906880 harness, that junction block just went from 175A to 400A circuit protection without any other changes, which doesn't seem very good to me.  

 

I can't find an upfitter wiring diagram that shows how this is handled at the X50A junction block in a single alternator diesel truck.  It only shows this junction block on the dual alternator diagram, even though I know it's there in both applications.  

 

In this situation, it might be best to determine an appropriate cable gauge to use to go between the batteries and just run my own custom battery cable with a 400A fuse and leave the factory junction block wire and 175A circuit protection in place for that junction block.  I hate to start disturbing very much of the factory wiring if I can help it.

 

Basically, I need to get two 400A mega fuses, appropriate cable size and terminal ends, auxiliary fuse block to go on top of the new battery and just leave everything else as-is.  Does this sound correct?

[Another JR]

I haven’t tried to look at the parts catalog pictures, but I’m quite sure the wire from the main battery fuse block to the main fuse box is not branched off the inter-battery cable. The fuse box has its own supply wire all the way back to the start battery fuse block. The two wires might be bundled together, but are separate. 
 

 

[Another JR]

10 hours ago, hsfdchief200 said:

 

 

 

Basically, I need to get two 400A mega fuses, appropriate cable size and terminal ends, auxiliary fuse block to go on top of the new battery and just leave everything else as-is.  Does this sound correct?

Yes, that is all you need to do from a functional standpoint. However, cleanly connecting your new cable to the main battery fuse block and routing it out of the cover can be a challenge.