Charging Choice

[alano]

We just returned from 2 weeks in the Pacific Northwest where it was cloudy, rained a bit and campsites are often under trees. 200W of solar did what it could, but we needed the truck to do its part to keep the batteries happy - it didn't. The original separator seems to have gone wonky since we only got about 1 amp to flow to the batteries when the truck is running. (I have a current meter on the wire from the truck attached to a display mounted on the front window of the camper to monitor charging) The 1 amp was extremely constant regardless of camper battery voltage. Go figure.

Solution seems to be to toss out the old and replace it with... what? After research, I've narrowed my choices to two:

1) Renogy 40A DC to DC Battery Charger

2) Blue Seas 7611 Battery Link ACR

Factors:

Cost difference not an issue

FWC wiring and connectors from my 2010 GMC 2500 to my 2013 Hawk

Already have a solar controller that does a decent job of managing my AGM batteries

Not keen to run wires from camper to truck

REALLY tired of dealing with electrical issues with my camper. Want a mostly forget about it solution.

Thoughts?

Thanks,

Alan

 

[Vic Harder]

Alan, have you confirmed that the alternator can push more than 1A by bypassing your isolator and/or existing wiring? Some jumper cables maybe directly to the camper batteries?

The choices you list are both reasonable. Here are some factors to consider:

1) The camper batteries need about .5v more than their present voltage in order to charge. So if they are at 12.2V, they need 12.7 to charge.
2) The higher the current flow, the greater the voltage drop across the wires from the alternator to the house batteries.
3) Typical RV 4 conductor cable is 14AWG. Maximum free air chassis wiring for that is 32A, which maybe why FWC installs 30A breakers. See this: https://www.powerstream.com/Wire_Size.htm
4) Wire run length is about 25' to 30' from your alternator to the camper
5) Assuming you get 30A from your alternator, the voltage drop is a horrendous 4.56V at 30A , leaving you with just 8V at the batteries. The isolator knows this won't charge the batteries, and disconnects ... https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=8.286&voltage=12.7&phase=dc&noofconductor=1&distance=30&distanceunit=feet&amperes=30&x=35&y=19
6) This is why the stock wiring sucks!

You can put the Renogy at camper battery end, but you are not going to get 40A of charge out of it unless you upgrade the wiring. The losses are too big.

Nor is a different isolator going to help compensate for the losses just by itself.

To get efficient and safe charging from the alternator, you are going to have to upgrade the wires.

BUT, I hear people say, I DO get a charge from my alternator. Sure you can. The alternator may be pushing out way more voltage than 12.7. The current flow may be way lower too. Both together allows some charging to happen. But certainly not 30A worth, or the promised 40A from the Renogy.

 

[alano]

Vic,

Thanks for your answer. I used to see 5ish amps max from the setup before. Thinking about this I realized that you are totally right about upgrading the wiring regardless of the ACR vs DC2DC debate.

I went out and poked around the truck and camper, did a bit more online research and have a new choice:

1) Replace the existing power wires with heavier (4 AWG welding cable?) wire using the existing connector between the camper and the truck with its 10 AWG pigtails.

OR

2) Add a new power plug on the right side of the camper and truck bed (or move the old one - what to do with the hole?) since both the truck battery and the camper batteries are on that side.

Shorter wire run with new plug - probably less than half.

Can use a beefier plug.

My Hawk has the running lights so either have to figure that out or just deal with two connectors each time camper loaded / unloaded (about once a year). Big deal.

Anyone know any reason why moving to the passenger side wouldn't be a good idea?

Thanks,

Alan

 

[ClimberRob]

Good breakdown from Vic.

I ran 4 AWG pure copper welding wire, myself. Terminated at an Anderson-style connector driver side front inside the truck bed. Then replaced the stock 4WC wiring inside the camper with the same wire, leading into two Blue Sea 187-series 100A breakers/switches. At that point, 6 AWG Ancor marine + wire leads into a 30A Sterling programmable smart charger. Negative wire goes straight to a Blue Sea Power Post, which also connects to the camper battery and the main common negative bus. + wire out of Sterling charger goes to another power post, which also connects the shore power charger, solar, house, etc..

I highly recommend upgrading the truck to camper wire, and also highly recommend the Sterling unit. Expensive, but solid.

 

[Vic Harder]

Alan, retaining the 4 or 7 wire trailer plug for the running lights is a good idea. As ClimberRob points out, Anderson PowerPole connectors and 4g wire are great for carrying the heavy current for charging.

I'd try that first, with 100A BlueSea 185 series surface mount breakers on the alternator and camper battery end of the +ve cable first, before adding in a Sterling or Renogy DC2DC converter.

Moving the cable to one side or another is no big deal. Keeping the wires as short as possible is good.

Plug the old hole with Butyl putty or silicone.

 

[alano]

Thanks guys. I'm drawing up a schematic and making a shopping list. After inspection, it isn't really that big a deal to run new wire through the truck and coming in through the passenger side of the camper makes that quite simple. The biggest hassle will be probably be removing and replacing the camper to mount the connector inside the bed. Probably can do the whole job in one day.

Alan

 

[smlobx]

Vic et. al-

I think I’m having an issue as well and not trying to hijack this thread let me ask this very basic question...

Are you suggesting running a 4 AWG wire from the alternator to the bed where my camper (7 wire)plug is located?
Is there any fuses in this?

When I looked at the wire that was run for my truck to plug in I discovered it was pigtailed off the back of the bed then up to the front of the bed where the plug is. The total distance must be over 30 feet!

Thank you.

 

[Vic Harder]

Vic et. al-

I think I’m having an issue as well and not trying to hijack this thread let me ask this very basic question...

Are you suggesting running a 4 AWG wire from the alternator to the bed where my camper (7 wire)plug is located?
Is there any fuses in this?

When I looked at the wire that was run for my truck to plug in I discovered it was pigtailed off the back of the bed then up to the front of the bed where the plug is. The total distance must be over 30 feet!

Thank you.

I ran 2g wires (yes, two of them, one for the +ve side and one for the -ve) from the truck battery (mounted driver's front of underhood area).

The +ve wire goes about 6" to a 100A Blue Sea 185 series surface mount breaker. Then continues on (with the -ve cable) under the truck cab all the way to the bed of the truck. It comes up into the bed via two 1/2" holes with bushings in them to prevent chafing/shorts. It comes into the bed about 18" and terminates in an Anderson Power Pole connector. A matching connector then takes the two cables into the camper via new holes in the wooden floor pack, sealed with Butyl rubber. The wires go over to the battery box area, where the +ve cable again meets a 100A breaker. The +ve then goes to a Blue Sea ML-ACR and from there to the rest of the charging electronics.

 

[ClimberRob]

Alan, retaining the 4 or 7 wire trailer plug for the running lights is a good idea. As ClimberRob points out, Anderson PowerPole connectors and 4g wire are great for carrying the heavy current for charging.

I'd try that first, with 100A BlueSea 185 series surface mount breakers on the alternator and camper battery end of the +ve cable first, before adding in a Sterling or Renogy DC2DC converter.

Moving the cable to one side or another is no big deal. Keeping the wires as short as possible is good.

Plug the old hole with Butyl putty or silicone.

Vic, I think you are recommending the 285 series breakers? They are very good, as well. I like the 187 series because of the location of both studs on the bottom, as well as the fact that they are designed to be used as a switch, in addition to the breaker functionality.

 

[ClimberRob]

Vic et. al-

I think I’m having an issue as well and not trying to hijack this thread let me ask this very basic question...

Are you suggesting running a 4 AWG wire from the alternator to the bed where my camper (7 wire)plug is located?
Is there any fuses in this?

When I looked at the wire that was run for my truck to plug in I discovered it was pigtailed off the back of the bed then up to the front of the bed where the plug is. The total distance must be over 30 feet!

Thank you.

As Vic suggests, run the cables off of the truck battery, or second truck battery if you have one. Don't run directly off of the alternator. Put a breaker or fuse on the + line, at least. Both wires is preferred.

4 AWG is likely plenty, unless you are pushing a ton of amps. You probably wouldn't want to do that, unless you have several batteries in a bank in your camper. Under "normal" charging conditions of one or two batteries, 4 AWG won't cause you any issues.

 

[Mthomas]

I am also interested in increasing the rate of charge to my house batteries from the alternator when driving/running. My diesel has an over 200 amp alternator, and should be able to supply some decent current. I am a bit of an electrical newby and had a couple questions. This is not meant as a criticism, just trying to understand:

1. why such high amperage breakers? I do not think anything in a FWC draws over 30 amps. I believe the current MPPT supplied by FWC only draws 15 amps and most of the smaller units I have seen people using for these solar systems draw 30 or less, so that would be it for charging from the alternator, wouldn't it? Wouldn't it make sense to have a breaker trip well before the max draw of the charger?

2. I also do not understand the rational behind a breaker on both ends of the supply wire.

3. What is the purpose of a breaker in the ground return to the batteries?

 

[ClimberRob]

I am also interested in increasing the rate of charge to my house batteries from the alternator when driving/running. My diesel has an over 200 amp alternator, and should be able to supply some decent current. I am a bit of an electrical newby and had a couple questions. This is not meant as a criticism, just trying to understand:

1. why such high amperage breakers? I do not think anything in a FWC draws over 30 amps. I believe the current MPPT supplied by FWC only draws 15 amps and most of the smaller units I have seen people using for these solar systems draw 30 or less, so that would be it for charging from the alternator, wouldn't it? Wouldn't it make sense to have a breaker trip well before the max draw of the charger?

2. I also do not understand the rational behind a breaker on both ends of the supply wire.

3. What is the purpose of a breaker in the ground return to the batteries?

Pick a breaker that fits your individual system and needs. If you are charging straight off of your truck without a DC-DC charger and have a large enough wire, you will likely be pushing more amps than is healthy for your battery. 25 amps is a maximum safe charge to push into a single 100 AH AGM battery, for example.

A breaker on both ends of the wire will limit damage to the truck battery, as well as camper battery. If you only have breakers on one end, one of the batteries would still be connected to that wire once the single breaker trips.

An issue with the negative wire can lead to arcing, increased resistance, and possible fire. Isolating that wire with a breaker is simply additional insurance.

 

[Vic Harder]

My diesel has an over 200 amp alternator, and should be able to supply some decent current.

1. why such high amperage breakers? I do not think anything in a FWC draws over 30 amps. I believe the current MPPT supplied by FWC only draws 15 amps and most of the smaller units I have seen people using for these solar systems draw 30 or less, so that would be it for charging from the alternator, wouldn't it? Wouldn't it make sense to have a breaker trip well before the max draw of the charger?

2. I also do not understand the rational behind a breaker on both ends of the supply wire.

3. What is the purpose of a breaker in the ground return to the batteries?

1) Yes, you alternator will supply all the current that will go into any potential load connected to it.

The biggest load -- and the reason for the bigger wires -- is your camper battery. Assume for a minute that the camper had been drawing 10A all night, and over a 10 hour period your camper battery was nearly completely discharged. So, it is 100AH short of "Full". Your alternator will try to push all 200A into that empty battery as fast as it can. With my 130A alternator and a 250AH camper battery bank, I saw 90A when the batteries were at 55%. That's a lot of juice!

2) Likewise, both ends of the +ve wire are connected to batteries. The breakers protect that wire and your life by being able to disconnect either/both ends of the wire from any battery.

2) Not sure I get the ground wire breaker thing myself. I haven't seen/done that myself.

 

[Mthomas]

interesting ideas in this article, follow the link back to his blog.
https://cookfb.files.wordpress.com/2015/04/enhanced-camper-battery-wiring-scheme.pdf

 

[Vic Harder]

Sounds very similar to what others here are saying. keep in mind that this guy has a huge battery bank. 2/0 AWG is not necessary for the typical FWC without an induction cooktop. he is recovering 150AH of overnight use. most of us are using 10-45 AH.

 

[ClimberRob]

2) Not sure I get the ground wire breaker thing myself. I haven't seen/done that myself.

Vic,

A fuse or breaker in the negative wire protects the conductor/wire. There are various scenarios where the negative wire can become a serious hazard. A fuse on the positive side will sufficiently protect the equipment. Fuses/breakers on the negative side will isolate the wire and protect the operator. You could also place a diode on the negative side, if you find that easier.

 

[rando]

I can't really think of a scenario where a fuse/breaker on the negative wire would be required or help. If there were to be a short on the negative wire (which would have to be a short to a positive wire) then the the current would also have to flow through the positive wire, and the fuse/breaker on that wire would trip.

The only place that I can think of where fuses are commonly used on ground wires is for equipment (usually ham radios) that have a multiple grounds (negative wire and antennas) that are wired directly to the battery with skinny wire. This is done so on the off chance that the ground strap on the battery breaks and you try and start the car, it could pull the starter current through the radio. This is not an issue in the camper scenario as there is only one ground (the cable we are talking about) and it hefty enough to handle the current anyway.

A diode is also not going to work - the ~0.7V drop across the diode would kill the ability to charge the camper battery (not to mention getting super hot at 30+ Amps).

Is there a scenario I am not considering here?

 

[ClimberRob]

There are quite a few ways you could end up with current flowing through the negative wire. Reverse polarity hookup, shorted battery (internally), etc. People hook up equipment improperly quite often, which can result in a short.

Many 12v electronics have a 16v diode across the negative connection. It works quite well. Obviously a fuse or breaker is the correct choice for the battery connection.

 

[rando]

In all these scenarios, wouldn't the same current be flowing through the positive wire to the camper battery, and therefore be protected by the circuit breakers on that wire? The only reason you would need a separate breaker on the negative would be in the case where you could have an (excessive) current flowing on the negative wire which is not also flowing on the positive wire. I can't think of any scenarios where this would be the case.

Not trying to be argumentative here, but trying to make sure we are giving good advice. A breaker on the negative for a dual battery is not something I have ever run across before, so I want to make sure it actually serves a purpose and that I am not missing something.

 

[ntsqd]

Rando beat me to it. Ham radios usually have a fuse in the ground wire. It is there mostly to protect the radio from reversed polarity. Ask me how I know this.

I used 285 series 80A breakers, an Anderson SB120 connector, and 6 ga. Ancor paired cables. I chose the paired cables because they have an extra layer of insulation to protect them from road debris and chafing - AND I detest split loom. I arrived at 6 ga. from measuring the total circuit length and assuming 80A max charge, then consulting Ancor's technical page on sizing DC conductors. Run cable for the full circuit length, don't try to ground to the truck's frame or something.

A lead- acid battery's internal resistance will self limit the max actual charge rate. They're not super-capacitors. No knowledge if you're using one of the more advanced chemistry batteries.