"Manual" Battery Isolator

[Steve Scearce]

First of all, this is my first post and I want to thank the members for a lot a useful information I have gleaned from your threads.

A little background: my wife and I just bought a used Phoenix popup and I've been been making some adjustments to make the camper work with our 2003 Tundra. I am going to use 10 gauge wire to hook up the truck battery to the camper battery for charging while driving. Rather than install an isolator, I'm simply going to install a pretty heavy duty plug on the camper so I can "unplug" from the truck charging system when we park, and switch the 3-way fridge to propane. I'll be the "isolator." Here's my noob question: what size inline fuse should I use?

Thanks in advance for being patient with a neophyte.

-DurangoSteve

 

[HERR42]

First of all, this is my first post and I want to thank the members for a lot a useful information I have gleaned from your threads.

A little background: my wife and I just bought a used Phoenix popup and I've been been making some adjustments to make the camper work with our 2003 Tundra. I am going to use 10 gauge wire to hook up the truck battery to the camper battery for charging while driving. Rather than install an isolator, I'm simply going to install a pretty heavy duty plug on the camper so I can "unplug" from the truck charging system when we park, and switch the 3-way fridge to propane. I'll be the "isolator." Here's my noob question: what size inline fuse should I use?

Thanks in advance for being patient with a neophyte.

-DurangoSteve


30 amp.

if you attempt to start the engine while plugged in i expect you will pop the fuse. be careful.

let us know how that works for you.

 

[pods8]

I'd say get a battery switch for $20 or so, it'd be safer and hold up over time me.

 

[EdoHart]

30 amp.

if you attempt to start the engine while plugged in i expect you will pop the fuse. be careful.

let us know how that works for you.


I agree completely with Jeff about starting the engine while plugged in. If you go this route, you might want to put a red "remove before flight" ribbon on the plug and ensure it's in a highly visible location that you will see before turning the key.

 

[Steve Scearce]

Thanks for all your input. I'm leaning toward a simpler, safer method: hooking the camper battery to the 7-pin connector that's part of my towing package. I checked in the fuse box and there's already a relay and a fuse for the charging line.

 

[EdoHart]

I should have brought this up before. How much did you pay for the camper? That is a rhetorical question, don't answer it. Do you really want to now save a small percentage of what you paid for your camper by not buying an isolator and instead trust your memory to disconnect and re-connect your campers batteries?

My advice is that if you have paid good money for a truck camper, spend a little bit more for an isolater. The first time you run down your starting battery(ies) while camping, you will wish the disconnect from your camper battery(ies) had been automatic.

 

[DLN]

I couldn't agree more Ed, the isolator system is idiot proof and I've been known to need idiot proofing at times.

 

[John D]

DurangoSteve, Great handle.

Mount the battery under the hood and run a two conductor 10 or 12 gauge romex back to the camper plug in. Do not use the 7 pin connector at the rear of the truck. You need to have the battery as close as possible to your alternator because the voltage loss on a long wire is significant. If you are attempting to charge the battery in parallel with the other under hood battery hanging out there on a long wire, it will never be more than half charged.

By mounting your second battery under hood, you can disconnect it as you please and it will function pretty well in parallel. However, you really need a way to charge each battery individually. The style of usage will be different between batteries where one is used as the "house" battery and the other is used as the "Starting" battery. Thus, it is really essential to have a way to switch batteries. What folks are telling you is entirely correct about having some kind of isolator, preferable a three position switch made for the purpose, either mechanical or electronic, as the case may be.

Again, the least expensive solution is a dual alternator set up. Each battery has its own alternator. This is by far the best solution and another way to isolate the two batteries. If you have a dual alternator set up, you can then place the battery in the camper without any worries about popping fuses, losses over a long wire, and other things. Dual alternators is the elegant, and probably the least expensive solution in the long run.

John D

 

[HERR42]

DurangoSteve, Great handle.

Mount the battery under the hood and run a two conductor 10 or 12 gauge romex back to the camper plug in. Do not use the 7 pin connector at the rear of the truck. You need to have the battery as close as possible to your alternator because the voltage loss on a long wire is significant. If you are attempting to charge the battery in parallel with the other under hood battery hanging out there on a long wire, it will never be more than half charged.

By mounting your second battery under hood, you can disconnect it as you please and it will function pretty well in parallel. However, you really need a way to charge each battery individually. The style of usage will be different between batteries where one is used as the "house" battery and the other is used as the "Starting" battery. Thus, it is really essential to have a way to switch batteries. What folks are telling you is entirely correct about having some kind of isolator, preferable a three position switch made for the purpose, either mechanical or electronic, as the case may be.

Again, the least expensive solution is a dual alternator set up. Each battery has its own alternator. This is by far the best solution and another way to isolate the two batteries. If you have a dual alternator set up, you can then place the battery in the camper without any worries about popping fuses, losses over a long wire, and other things. Dual alternators is the elegant, and probably the least expensive solution in the long run.

John D


10 ga wire runs about an ohm per thousand feet. that 7 pin rv plug is specifically designed to charge a battery in a towable. and it will do a good job and fully charge a battery.

but, for a camper its not a good solution.

look over how ATC,FWC do theirs and copy the approach....it is a good one.

 

[pods8]

Again, the least expensive solution is a dual alternator set up. Each battery has its own alternator. This is by far the best solution and another way to isolate the two batteries. If you have a dual alternator set up, you can then place the battery in the camper without any worries about popping fuses, losses over a long wire, and other things. Dual alternators is the elegant, and probably the least expensive solution in the long run.

John D


While a dual altenator would be a nice set up I don't think its anywhere near the ballpark of "least expensive solution". Most of the kits I've seen (assuming they even make one for your rig, my truck they don't) are $500+.

I'll be finishing up wiring my powerstream DC-DC charger tonight and testing it for 2 weeks when we roll on Saturday. Charge rate is limited to 7.5amp which might not be ideal for some folks but if you're only pulling 20-30amps a night and most destinations take a bit of driving to get to I'm thinking it'll work decently. I'll have about $200 in the charger and wiring when said and done. The benefit is unlike a dual altenator the charger actually does a stage charge which deep cycle batteries like.

I didn't get into whether or not a manual switch was a good idea in this thread because he didn't ask about that but I agree its not an ideal.

 

[Steve Scearce]

Thanks for the insights. I'm obviously new to this stuff, which I suppose goes without saying. Transitioning from tent camping, you know...

I have shortterm and longterm goals regarding the "house" battery. Shortterm, I'm looking to keep the Everstart deep cycle house battery (115 amp hrs) that will be fully charged before leaving home, from being drained on our average 3 hr drive to SE Utah from Durango. Looks like the Norcold 323 fridge sucks 11.7 amps. IF I were to take the easy way out (shortterm) of using the 7 pin connector to provide the house battery with juice will driving, which I will unplug when we arrive at camp, will I adequately compensate for the fridge's drain on the house battery during the drive?

Longterm I'm considering adding solar and getting serious about electrical issues OR yanking the 3-way fridge and just using a cooler. I'm pretty damned good at cooler mgmt from years of car camping and river running. At this point, the 3-way tiny fridge strikes me as a royal pain in the ass, and a consumer of valuable storage space.

Opinions?

Steve

 

[pvstoy]

I have not used DC for the fridge for years. Use AC at home to pre cool then Propane for the whole trip. The Casita I own I have never tried the DC mode, don't know if it even works.

 

[pods8]

I have shortterm and longterm goals regarding the "house" battery. Shortterm, I'm looking to keep the Everstart deep cycle house battery (115 amp hrs) that will be fully charged before leaving home, from being drained on our average 3 hr drive to SE Utah from Durango. Looks like the Norcold 323 fridge sucks 11.7 amps. IF I were to take the easy way out (shortterm) of using the 7 pin connector to provide the house battery with juice will driving, which I will unplug when we arrive at camp, will I adequately compensate for the fridge's drain on the house battery during the drive?


For starters I switched over to pvstoy's propane relighter mod and just run the fridge on propane all the time (unless I'm on shore power, ie AC power).

If you were wanting to run it on 12V while moving I'd personally rewire the fridge so the 12V never saw your camper battery, that way you'd never accidentally kill it. Run a new line from the truck battery to the fridge that is on an ignition hot switch relay or solenoid such that it only gets 12V when the vehicle is running which will protect the vehicle battery as well. This way you'll not drain either with that fridge. However if down the road you ditch the 3way and go to a DC compressor fridge you'd need to rethink things to power off the camper battery.

 

[John D]

pods8, Let me take this opportunity to add more in attempting to state a case for dual alternators.

Electronic isolation is somewhat limited by a property of semiconductors whereby there is no perfect one way bias in a transistor or diode. Though a computerized switching device can provide better isolation, such systems are rather fragile and have limited power loading. This is not satisfactory when batteries can benefit from heavy recharging currents upwards of 50 amps in each battery.

The statement about a 10 gauge wire having one ohm resistance per thousand feet raises questions about what load, voltage, and temperature? Furthermore, it is my impression, that the 7 pin connector circuit uses 14 gauge wire.

Regarding mechanical switches, they require some degree of human attention. As we know, people make mistakes that can result in either discharging both batteries simultaneously or accidentally disconnecting the alternator from both batteries, possibly damaging the alternator.

We are not addressing the shore power charging system here, but it adds an additional complication. Shore power systems are much better than they once were, but they may be challenged with the same old problem of charging two batteries at the same time.

About costs; Delco use to make very good 60 amp alternators with internal regulators that could be purchased rebuilt from Autozone for about $25 each. The mounting brackets are the most expensive part of the dual alternator system. A standard Delco alternator provides regulated power through a single wire.

Of course, new alternators are more expensive. pods8 is correct in estimating a cost up to $500 assuming all new alternators and other custom components. To balance against this, there are costs with a single alternator system that have not been addressed. For example, if a vehicle is disabled on the White Rim Trail, wrecker services to retrieve it will exceed $1000. All things being equal, a dual alternator system is at least 4 times as reliable as a single alternator system. How much is the greater reliability worth?

John D

 

[pods8]

The statement about a 10 gauge wire having one ohm resistance per thousand feet raises questions about what load, voltage, and temperature? Furthermore, it is my impression, that the 7 pin connector circuit uses 14 gauge wire.


I didn't make that statement and usually go on voltage drop charts for a given current in a wire size personally. When dealing with batteries when you start loosing a few percent voltage it makes a difference.

The stock wiring on a 7 pin is likely something smaller like 14ga so if one was planning to use the stock 7 pin many resources recommend running a new heavier gauge line. The housing can be rewired for heavier gauge.

Regarding mechanical switches, they require some degree of human attention. As we know, people make mistakes that can result in either discharging both batteries simultaneously or accidentally disconnecting the alternator from both batteries, possibly damaging the alternator.


No arguments here.


We are not addressing the shore power charging system here, but it adds an additional complication. Shore power systems are much better than they once were, but they may be challenged with the same old problem of charging two batteries at the same time.


Well now we're jumping out of the original discussion but there are numerous battery chargers out their with dual (or triple) leads so each battery gets its own charge.

About costs; Delco use to make very good 60 amp alternators with internal regulators that could be purchased rebuilt from Autozone for about $25 each. The mounting brackets are the most expensive part of the dual alternator system. A standard Delco alternator provides regulated power through a single wire.


Yeah a rebuilt altenator is cheap but I'm guessing the mass of folks aren't going to be able to design a reliable mounting bracket that fits somewhere into a modern engine bay in a place that allows it to be tied into the belt system while still allowing all the other components to operate properly. With that in mind we're stuck with kit pricing when discussing the costs of a mass implementation suggestion.

To balance against this, there are costs with a single alternator system that have not been addressed. For example, if a vehicle is disabled on the White Rim Trail, wrecker services to retrieve it will exceed $1000. All things being equal, a dual alternator system is at least 4 times as reliable as a single alternator system. How much is the greater reliability worth?


The discussion is wandering here. Granted there are external issues that can be factored in but you can't just make the statement a dual alternator is the cheapest solution at face value.

***All that said I am a fan of them and I'd encourage anyone interested that has the money and vehicle to accommodate one to pursue if they want one. Just trying to clear up some statements which I considered to have been painted a tad broad at first.

 

[John D]

pods8, We are discussing recharging batteries in prose. If we follow academic tradition, prose is more precise than speech. However, this forum is conducted as if it were speech rather than prose. In speech it is acceptable to exaggerate to make a point. I am guilty, as in implying that losses with a number 10 wire are minimal. And, I agree that 25 dollars for an alternator is less than most would end up paying. A complaint about wandering is also argumentative, but, I did it. Therefore, I agree that you are correct in your statements.

A new guy is asking what to do about charging a deep cycle house battery. There are several correct answers, including charging it up at home on a battery charger, not bad for a short trip. Unfortunately, there is no perfect solution for his problem.

If Durangosteve knows from this discussion not to be surprised with a poor performance from his batteries, either sooner or later, he will have learned enough. _John D

 

[pods8]

Unfortunately, there is no perfect solution for his problem.


When it comes to batteries there have never been truer words spoken!





I am almost done packing and then off to wander in the AM.

 

[HERR42]

my ford's 7 pin rv plug is wired with 10 ga for the +12 charge pin. this is factory wiring.

i am sorry but, this statement is grossly incorrect.

"Electronic isolation is somewhat limited by a property of semiconductors whereby there is no perfect one way bias in a transistor or diode. Though a computerized switching device can provide better isolation, such systems are rather fragile and have limited power loading. This is not satisfactory when batteries can benefit from heavy recharging currents upwards of 50 amps in each battery."

here is proof -> http://www.hellroaring.com/ read up on their solid state isolator

and keep in mind that both Interstate and Optima specify a 30 amp limit on charge current on AGM batteries.

i have dual alternators, and it does not solve the problem at hand.

adding a 2nd alternator simply makes more charge current available. the problem is controlling the delivery of that charge current to multiple remote batteries.

 

[John D]

HERR42, I am curious about how your dual alternators are wired. Yes, I agree dual alternators provide extra power. I was talking to a friend who owns an alternator shop who had a guy come in with six alternators! He was powering a big sound system in his car. From what my friend said, the mounting and belt system was interesting. (I bet it is the same guy who drove by my house in the middle of the night and knocked me out of bed with his subwoffers.)

The dual alternator arrangement I am suggesting would be wired to provide two independent charging systems. This concept leaves the truck's charging system without any modification or additional load. The second alternator is mounted to provide power to the camper battery ONLY. To illustrate the concept, it is possible to size the second alternator to match a light load from, perhaps, a deep cycle battery in the camper.

Yes, both alternators are grounded to the same truck. It is the outputs that are separate. This takes advantage of modern voltage regulators in truck charging systems that are almost uncanny in their ability to keep batteries properly charged because they have evolved for exactly that purpose over many years. I won't say a dual alternator system does a BETTER job than the latest electronic isolators because I don't know. However, I would be surprise if they did not.

There are other dual alternator arrangements. For example, if anyone has seen under the hood of a military M1009 Commercial Utility, Cargo Vehicle (CUCV), which is a military Chevy truck from the 1986, you will note two alternators. These are wired to provide 24 volts in order to make these civilian trucks compatible with military electronics while using mostly civilian hardware. It is clever. My M35A2, as an example of a pure military vehicle, has a single alternator providing 24 volts. Both these vehicles use two 12 volt batteries in series. A M1009, M1010, etc. in the junk yard might provide the mounting hardware for your second alternator very inexpensively. (These are diesel trucks and I don't know if the mounting hardware is unique to their engines.) John D

 

[HERR42]

both alternators (each house its own voltage regulator) feed in parallel to the trucks dual battery system.
the pcm controls each alternator.

From Ford's Service Manual:

"The optional dual generator package (7.3L diesel engine only) consists of an upper/lower dual generator system. The upper generator is a 6G 50/110 generator with a 2.49:1 pulley ratio. The lower generator is a 6G 50/110 generator with a 2.32:1 pulley ratio. Thus the upper and lower generators are not interchangeable.

This system is also monitored and controlled by the powertrain control module (PCM). The PCM monitors both the upper and lower generator I circuits to determine both generators' output and set possible fault codes (diagnostic trouble codes [DTCs]). The PCM only controls the lower generator by turning it on or off by opening or closing the lower generator off only when the glow plugs are commanded on by the PCM to avoid possible damage (excessive voltage) to the glow plugs.

Both generators are independent of one another and only control themselves (through their own internal voltage regulator). If one generator fails, the other generator can maintain system performance under light load conditions. Under a heavy load, the PCM should detect a problem, set a DTC and illuminate the warning indicator.

The PCM controls the charging system warning indicator and will command the light on if the PCM detects a problem on the monitored circuits. "