Questions about continuous duty solenoid

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Lizzarro

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So as I'm getting everything installed I picked up a continuous duty solenoid to keep my batteries topped up on days when I can't get good solar. Problem I have is that I have no idea how heavy cable I need or what fuse to put on it. 

It will be about 20-25 feet to route the cable between my house batteries and the front of the van. I'm worried if I buy too light things might get hot, and a 25ft run concerns me.

Is there a possibility of putting extra strain on the vehicle's charging system if I buy too thick?

Is it better to have my power flow from the battery positive or directly from the alternator?

Is there any harm in making a jumper that I can use between the house side solenoid post and the battery positive to combine the batteries manually in the event my starting battery runs flat?

My vehicle's starter battery is an AGM, do I risk shortening its lifespan by diverting some of the alternator power away from it? I've heard they like higher current.
 

MrNoodly

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Lizzarro said:
...to keep my batteries topped up on days when I can't get good solar...

...when you will be driving. Otherwise, there's no charging happening.

But, to answer your question, the cables to your house battery should be as thick as the ones already on your vehicle battery.
 

SternWake

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It takes time to fully charge a battery.  80% to 100% charged is no less than 3 hours no matter how powerful the charging source might be, so topping up via alternator, is not something accomplished in 15 minutes of idling. I know this is contrary to the public mindset that the alternator is some free magical instant battery charger, that the rules of physics no longer apply.


For best recharging performance, the thicker the copper the better, and the shorter the circuit, the better.  So it is better to take power from alternator (+) stud rather than engine battery.
1, this bypasses the too thin cabling provided by the manufacturer
2, this allows the voltage regulator to see than higher field current is required to raise system voltage, and hopefully allows it to keep seeking 14.4v rather than  prematurely dropping to 13.7v
3. Bypassing the engine battery, the circuit is usually significantly shorter.

A depleted healthy battery over adequate copper can max out an alternator.  This causes it to generate a lot of heat.  Temps over 220f are cumulatively damaging to an alternator.

An Alternator capable of high output at low rpms can cook if the vehicle's voltage regulator keeps demanding 14.x volts.  Idling to recharge means lower alternator fan speeds and limited underhood air movement and is hardest on the alternator.

Much variation from vehicle to vehicle.  My Dodge van alternator temperature skyrockets at max load at idle, but the same load at highway speeds has temperature down to cakewalk levels.

Yes you can make a jumper, across solenoid, or combine both cables to the same stud, or just feed 9+ volts to the trigger circuit on the solenoid.

Many circuits chosen to trigger a solenoid are live during engine cranking, meaning house battery is contributing current to starter motor.  This is not desirable and will wear the Main contacts in the solenoid much faster.  Find a circuit live only with engine running if possible, or put a lit manual switch to manually control the solenoid.  many different ways to trigger the solenoid.  If the Hvac blower motor turns off when engine cranking, this is a good trigger circuit for the solenoid.

AGMS like higher charge currents when depleted.  An  AGM used as an engine starting battery only in theory should never be depleted much, and as such could never accept huge charging currents, making this high amp recharge requirement of theirs in this application not worrysome.

If the engine battery is depleted and the house battery is depleted the batteries will share the current, but likely not equally. The AGM being lower resistance and on a shorter circuit, should pull more current, but there are of course variables which could make that untrue/ inaccurate.

I recommend using 2 digital voltmeters visible to the driver.  3 wire voltmeters with the third wire being a voltage sense wire hooked right to the battery (+). HOuse an engine.
 These will allow one to see how long it takes house battery to catch up to engine battery, and to see if/when the solenoid contacts fuse together rendering no isolation with engine off, AND if the house battery is contributing to starter motor current undesirably. 
It also reveals the wacky behavior of most vehicle voltage regulators.  While we dwellers would love to see 14.4v allowed any time the battery is depleted below 100%, the vehicles VR often will allow something much less, increasing charging times slightly to greatly.

The one thing to always remember is that the batteries require time to reach full charge, time at absorption voltage, and this time is considerable, and reaching 100% regularly is the key to good battery life.  reaching 90% only, will have the battery sulfate and lose capacity much much faster than if it reached 100%.

With 20 feet of wire one way to the house battery from alternator, I'd recommend 2awg or thicker cable. If you ground house battery to nearby frame, make sure the mating surfaces are shiny, the bolt threads also uncorroded, and use grease or liquid electrical tape.  Adding a ground cable from frame nearby alternator to alternator (-) or alt mounting bolt is also wise.  If not then the original engine battery to engine ground cable is carrying all the charging current to house battery as well.

Ideal ground path for house battery recharging would be another cable routed in parallel to the alternator (-) rather than using frame, but this is expensive and heavy and the percentage gained would only be realized when the house battery was depleted in the 50% range, and the vehicle was driving on the highway, where adequate rpms and underhood airflow could allow the alternator to max out and not overheat.

Idling unmoving to recharge is much  harder on the alternator due to the alternator fan not moving fast enough and not enough underhood airflow.
 

Lizzarro

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Thank you that's a ton of info and that addresses most of my concerns. I don't intend to idle to recharge but I figure it'd be a waste not to use the power I'm already generating while driving.

What kind of amperage can I expect to move during bulk charge? I'm asking with choosing a proper fuse in mind. I have a good bit of 1/0 laying around and will probably use that. Good reminder on beefing up the alternator ground too. 

Thanks again.
 

SternWake

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One fuses to protect wire. U ndersized fuses cause voltage drop
 

bcbullet

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I would only add one thing; although convenient to switch the solenoid with the vehicle ignition, there may be times where it is beneficial to do so with a separate switch inside the vehicle. You would need to think about whether you want control over tying the two sets together such as whether you wish to charge the starting battery with the house system, whether solar, charger or what have you.
 

GotSmart

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bcbullet said:
I would only add one thing; although convenient to switch the solenoid with the vehicle ignition, there may be times where it is beneficial to do so with a separate switch inside the vehicle. You would need to think about whether you want control over tying the two sets together such as whether you wish to charge the starting battery with the house system, whether solar, charger or what have you.

I followed SW's advice when I put my electrical together.  I have a switch coming off the "run" system that I only activate on long runs to do a heavy recharge on my batteries.  Definitely fuse it!

https://www.amazon.com/dp/B008R1T5I...UTF8&colid=2V2H86R4VLH9&coliid=I1UE8B7RJRQKUQ
 

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bcbullet

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GotSmart

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bcbullet said:
I did not mean to put a switch in line with the charging cable, I meant to switch the solenoid on/off from a separate switch in the cockpit.

Then the link I posted is to the unit you want.  

Fuse,  Power in from alternator,   ground,  on/off switching leg,  power out. 

I have my power for switching. (5 amp)  from a wire that activates when the motor is running The switch is on the dash.
 

Vagabound

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After watching the EN video about continuous duty solenoids to charge house batteries, the part that troubled me a bit was the fuse box connection.  Not the concept, but a way to do it that seemed better than gum and a paperclip and less work than drilling holes, possibly in the wrong place, etc.  Ran across the following connector.  Any good reason _not_ to use something like this to connect the solenoid to the fuse box?

Littelfuse FHA200BP ATO Add-A-Circuit Kit

Vagabound
 

Vagabound

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Optimistic Paranoid said:
How about the fact that it's limited to 10 amp circuits?

... vs. a more normal 30 amp circuit found in this application?

I suppose that putting a 30 amp fuse in it won't solve the problem due to wire size used while making it, or some other limitation?

Vagabound
 

Optimistic Paranoid

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Vagabound said:
... vs. a more normal 30 amp circuit found in this application?

I suppose that putting a 30 amp fuse in it won't solve the problem due to wire size used while making it, or some other limitation?

Vagabound

That would be my take on this, yeah.  A wire designed for 10 amps won't ALLOW 30 amps to flow.  It would be like splicing a bit of garden hose between two fire hoses.
 

ccbreder

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This fuse would be for the exciter circuit to the solenoid. That should not be near 10 amps.
 

ccbreder

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Ok. I clicked on the solenoid link. That solenoid is rated at 30 amps pass through. Not large enough for a alternator charging circuit. I would look for the ones that pass over 100 amps. The triggers are all about 1/2 amp.
 

Vagabound

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ccbreder said:
This fuse would be for the exciter circuit to the solenoid. That should not be near 10 amps.

Just to confirm, are you saying that, while the overall charging system (alternator to house batteries, etc.) might be at 30 amps, the small connection from the solenoid to the fuse box would be smaller, at around 10 amps?  Sorry, just beginning to learn about this.

Vagabound
 

highdesertranger

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ok I think Vagabound is talking about the when they tapped into the fuse box to trip the solenoid. if that is correct then that fuse jumper he showed would work fine.

yes you need at the very least a 80 amp solenoid but bigger is better in this situation, a latching solenoid is also better. highdesertranger
 

SternWake

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A 100 amp NON latching solenoid consumes about 0.8 amps to energize the electromagnet Which holds the large internal contacts together..


A latching solenoid requires only a burst burst of 12v to close and latch the solenoid, and another brief, momentary burst to unlatch it.

https://www.amazon.com/Momentary-N-O-Push-Button-Switch/dp/B0002ZPB34

This basically requires a light to tell the human whether the solenoid is latched or not.

I am not sure how to have a latching solenoid wired to be completely automatic.

Do not feed a latching solenoid a constant 12v.  It will overheat and burn out.

Get as high a amperage rating solenoid as you can find, within reason of course, Unless you got $$$ burning a hole in your pocket.

https://www.amazon.com/Blue-Sea-Sys...1475429164&sr=8-2&keywords=blue+seas+solenoid

The main contacts in solenoids can wear out.  Usually they fail with the main contacts fused together, and it will still make the same noise, or nearly so when energized, but there will be no battery isolation.  House loads can then cycle  engine battery reducing its lifespan and likely at some point, requiring the driver get a jumpstart.

When the contacts first fuse together, this is invisible to the driver, unless one has a voltmeter for each battery visible to driver( good idea anyway) or they actually test regularly for continuity across bigger studs on solenoid with a DMM.( digital multimeter) 

There are some voltage sensing solenoids which require no trigger input.  Get a single sense one if one employs solar, a dual sense one will consume solar current to energize magnet to hold batteries in parallel.

Surepower 1314 and 1315 are two automatic solenoid options.

There are a zillion battery isolator type products out there
 

ccbreder

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Vagabound said:
Just to confirm, are you saying that, while the overall charging system (alternator to house batteries, etc.) might be at 30 amps, the small connection from the solenoid to the fuse box would be smaller, at around 10 amps?  Sorry, just beginning to learn about this.

Vagabound

read my post at #15. About 1/2 amp for the exciter part of the solenoid.
 
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