Hi. I am planning on adding a dual battery set up to my truck and I had a quick question. Everywhere I am looking at recommends a solenoid to isolate the batteries. I currently already have a 120 amp relay installed tied to the ignition because I wanted more acc electronics. Would the relay do? Or would I need a solenoid? What is the difference between the 2? I’m hoping a relay would do because I would already have most of the components and work done. Thanks in advance.
Relay vs solenoid for dual battery
- Thread starter Liesejunh
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solenoid and relay are basically remote switches that use a low current to control a high current. solenoids are generally used for higher current around 40a and above (winch) and relays are more low current, like fog lights, horn, etc.
there are high current relays and the term solenoid and relay seem to be fairly interchangable...
here is a link that might be helpful for what you need
there are high current relays and the term solenoid and relay seem to be fairly interchangable...
here is a link that might be helpful for what you need
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Member III
Adding to what @grubworm said, When were talking about switching power, "Solenoids" are normally a higher power magnet with something to force the contacts together. Relays pull the contacts together and can have issues with high current flow.
A solenoid is normally an actuator used to move something. Your fuel injectors are solenoids, older vehicles had door lock solenoid's, pushing the lock linkage....... Your starter solenoid not only closes high current contacts but engages the drive gear.
The link he posted is similar to what I run, with mine being about 250 amp. I prefer solenoid switch's for anything high current.
A solenoid is normally an actuator used to move something. Your fuel injectors are solenoids, older vehicles had door lock solenoid's, pushing the lock linkage....... Your starter solenoid not only closes high current contacts but engages the drive gear.
The link he posted is similar to what I run, with mine being about 250 amp. I prefer solenoid switch's for anything high current.
Traveler II
I would suggest using whatever unit has the amperage rating that suits your build and use. A relay with 120amp capacity would suffice for simply charging the battery. Some of the basic ACR units are rated about 120amps. If you foresee yourself possibly needing (or wanting) the ability to 'self jump start' you will need something with a higher capacity. I personally used a 500amp solenoid in my dual battery setup. It works well for self jump starting.
The simplicity of a basic relay/solenoid battery isolation system is fantastic. There are no automatic systems to fail, any issue can be easily and quickly diagnosed in the field and if necessary it can be manually bypassed with little effort. I am going on 4 years with my basic setup with absolutely no issues. The only scenario that I would go with a DC-DC charger is when using batteries of different chemistry (AMG starting and Lithium House).
The simplicity of a basic relay/solenoid battery isolation system is fantastic. There are no automatic systems to fail, any issue can be easily and quickly diagnosed in the field and if necessary it can be manually bypassed with little effort. I am going on 4 years with my basic setup with absolutely no issues. The only scenario that I would go with a DC-DC charger is when using batteries of different chemistry (AMG starting and Lithium House).
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One thing to add, if you are going dual battery this way, ideally you want to have the same battery at the same age. I'm assuming AGM in this scenario, but mixing battery types and condition can cause earlier failures when combining via basic relay. An alternative is at least a smarter ACR which if I remember right has a delay to prevent a rush of current to the depleted house battery from the starter at ignition on. A smart isolator/charger is a good option in this case and while more $$ opens this up to a mix of battery types. Ie FLA starter with AGM house, or FLA starter and lithium in the cab etc.
With the prices of lithium batteries now, that seems to be the best route with 2k plus charge cycles and near 100% depletion and a fast charge. Look up "the road chose me" on YouTube and you can see his newest setup. I'll be going that route when I redo my dual battery.
With the prices of lithium batteries now, that seems to be the best route with 2k plus charge cycles and near 100% depletion and a fast charge. Look up "the road chose me" on YouTube and you can see his newest setup. I'll be going that route when I redo my dual battery.
For a little more money and marginally more complex, I'd recommend a smart solenoid over a regular solenoid. With a regular solenoid activated by turning your key to the ACC position, your batteries will be combined. In other words, your dead aux battery will be drawing from your charged main battery. At the same time, you are trying to power your vehicles high current starter.
A smart solenoid does not combine the two batteries until after the vehicle starts. It is triggered either by a ~13.2V voltage reading on your main battery (i.e. alternator charging) or it might have a timer delay and not combine batteries until after the vehicle has been started.
If you want to mix and match battery types, a DC-DC charger is a better approach.
A smart solenoid does not combine the two batteries until after the vehicle starts. It is triggered either by a ~13.2V voltage reading on your main battery (i.e. alternator charging) or it might have a timer delay and not combine batteries until after the vehicle has been started.
If you want to mix and match battery types, a DC-DC charger is a better approach.
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I used this for inspiration in setting up my dual battery system...
expeditionportal.com
How to make a cheap isolated dual-battery setup for $50
So there are a lot of kits you can buy to have truly isolated dual-battery setups. Those are VERY NICE kits. They are also very expensive. I try and replicate those kits without spending as much money, while still having a similar level of quality and/or reliability. There are constantly...
expeditionportal.com
Off-Road Ranger I
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I’ve been doing dual AGMs for 10 years. The first pair of batteries lasted 7 years. Everything on the system is controlled with a single manual marine grade switch, to either connect the batteries or isolate them. If I’m out in the middle of nowhere camped for multiple nights and I forget to isolate at night, and connect in the day for solar charging, that’s on me, my mistake. When a solinoid fails it’s on the solinoid manufacturer, the warranty doesn’t do you a whole lot of good when you’re a day or twos drive from the nearedd see t town. If you do decide to dump piles of money into your set up, remember to set it up so you can bypass any faulty device if needed. I’ve been out with more than one person who’s system failed and they had no way to bypass it. Not a good tour for either of em.
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I agree with this, but still, I prefer a manual switch. They never fail.I used this for inspiration in setting up my dual battery system...
How to make a cheap isolated dual-battery setup for $50
So there are a lot of kits you can buy to have truly isolated dual-battery setups. Those are VERY NICE kits. They are also very expensive. I try and replicate those kits without spending as much money, while still having a similar level of quality and/or reliability. There are constantly...
Automation exists in part to reduce human error. If the solenoid fails, a simple 4" pigtail can connect the batteries and bypass the smart solenoid. I'd be interested to know what kind of system your friend had that had no way to bypass it. Nobody brought jumper cables?
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he had a Red Arc system installed by a shop. He knew nothing about it. His house battery was in the rear of the vehicle, the red arc under the hood. The starter battery was fine, the solar charger worked, it just would not charge the house battery while touring. Short story - about 15 years ago the no idle laws for big trucks kicked in. The new Freightliner assigned to me had a 6 pack of AGM batteries to run interior lighting, heating and a/c with a solenoid between the house battery pack and the starter batteries. All told there were 9 batteries. I was in Halifax and woke up cold about 4am. It was minus 25*f. The truck would not start, the solenoid failed. I was behind a strip mall with nothing open until 7. I got my survival gear out, got into my bag and waited till 7. From then on, company policy and no idle laws be damned, I idled the truck in cold weather. I’ll roll the dice with human error over mechanical failure.
+1
In my experience there are far fewer failure modes in manual control than there are in automatic control. Fundamentally, automatic systems have more ways to go wrong. Just compare an automatic transmission to a manual transmission.
And then there is the matter of holding someone responsible. I can easily hold myself responsible, but good luck finding the individual (or more likely team of numbskulls) responsible for the failure of some automagic widget. I am much happier looking in the mirror and knowing who is responsible than I am just shrugging and thinking "Oh well, who knows who messed up." Funny thing is, I suspect most of the world prefers the opposite choice.
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I think that if Americans understood that they do have a choice, which is not an easy concept to grasp, let alone understand, most people, would choose simple, effective & efficient instead of complex, fails occasionally, and only efficient when it’s working properly. (Ironic humor at its finest when a very expensive, complex thing fails a day or 3 weeks into an off highway trek down a trail/track and one hasn’t a clue how to fix it )
More folks need to read Kon Tiki and Brendan Voyage. In both voyages one of the unavoidable lessons was the superiority of the old ways of doing things, in no small part on account of their ability to be easily repaired or adapted according to needs. The Achille's Heel of all these newfangled devices is their dependency on fragile components which cannot be repaired in the field.
The Redarc unit is a DC-DC charger, still simple but not the super simple solenoid we've been talking about. In any case, the installer would have ideally installed it next to the house battery (in the rear). All fails, just bypass the DC-DC charger and connect the power leads straight to the house battery. It'll charge it, not 100% but it'll charge it some. Even taking the charge cable from a 7-pin tow harness will charge the house battery.
Comparing a solenoid to a manual switch is not same as comparing an auto vs manual transmission. Anybody who has an old classic car with fully manual headlight switch and no warning chime will certainly leave their headlights on at some point and kill their battery.... no start condition. This is the same. Who would prefer to buy a new car today that doesn't have automatic shut-off headlamps?
Don't get me wrong, I appreciate keeping it simple for an overland vehicle. I drive one of the simplest overland vehicles, a 70 series Land Cruiser, diesel with manual transmission. It'll even run with NO batteries. But you know what? It does have non-auto shut-off headlamp switch that will indeed kill the batteries if by human error, I leave them on. I intend to change that.
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ME!!!
The newest vehicle I own is 20 years old. I refuse to buy anything newer. I do not want the features.
The '97 ZJ I bought for The Varmints to drive has too many modern features for my taste. And guess what? Those modern features kill the battery. I bought the thing for $1,000. Relatively cheap. Because the owners couldn't keep a charged battery in it. It has some silly circuit that is supposed to keep the dome lights on after you shut it off or some such thing. We spent most of a day isolating the circuit with that drain and pulled a wire out of a big honkin' plug to fix that problem. For icing on the cake, killing that circuit also killed the headlights-are-still-on chime. The Varmints have yet to come out to find they have a dead battery.
But, for the record I am a dinosaur. No cell phone. No texting. You can write me off pretty easily. At best I am an outlier.
Haha, well, okay. My oldest car is 50 years old. No power brakes, no power steering, no power locks/windows, not even a heater (I removed it and welded the firewall holes shut). But that fancy headlight circuitry is going in. Some things are just worth the added complexity! haha. I went EFI over Carb too.
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This thing, works well, it is a VSR, it will only connect the batteries if the Alternator is running. I had something similar when I had an AGM as a house battery. If you place it somewhere between the batteries in a visible place, you can always tell if it is working or not from the status LED. And you can bypass it easy, just have a spare a small bus bar or even better, an inline 50-60 amp fuse.
This are simple basic devices.
On the other hand, a horse might be more reliable, and a donkey less maintenance for sure. Can also climb higher and tackle more difficult terrain, but they have little payload so you will need 2 of them, ...
Pro's and con's..., there is always some kind of kink somewhere.. it never ends.. :)
This are simple basic devices.
On the other hand, a horse might be more reliable, and a donkey less maintenance for sure. Can also climb higher and tackle more difficult terrain, but they have little payload so you will need 2 of them, ...
Pro's and con's..., there is always some kind of kink somewhere.. it never ends.. :)
