starting system/house system - thinking about connecting them

[anm]

I have wired the house system so that it is completely independent from the starting system, other than being housed in the same vehicle. But now I'm thinking about connecting the systems together through a solenoid that would be controlled by the mobile home owner. The advantages to this are:

1. If the SoC of the house battery is too low then the van's alternator can charge it.
2. If the starter battery is inadvertently partially discharged the house battery can be used as a 'jump-start' battery.
3. The house system can also charge the starting battery from the solar panels.

The disadvantages are:

1. I don't want to rely on the alternator to keep the house battery charged.
2. Or rely on the house battery for starting.
3. An added strain is placed upon the van's alternator if it has to routinely charge the house battery.

How I would wire it:

1. Connect the positive side of the starting battery to the solenoid using 6awg wire.
2. Connect the positive side of the house battery to the other side of the solenoid using 6awg.
3. Run a 6awg ground wire from the negative side of the house battery to the frame somewhere.
4. Connect a toggle switch to the coil of the solenoid, and the other side of the switch to the starting battery (through a fuse), using 18awg wire.
5. Ground the other side of the solenoid coil if necessary.

I am planning to not use any fuses in the 6awg wire since it can be expected to supply starting current on rare occasions. I know that the 6awg run is about 10 feet, but it will be passing a starting current only very rarely, and that for a short interval. When used to charge the house battery it may briefly hit 40-50 amps, but then drop back fairly quickly. If the house system is being used to charge the starting battery the current in the 6awg wire will only be 10 amps or so.

I have looked at jumper cables in AutoZone and my 6awg wire is heavier gauge than all but the most expensive jumper cables. I think the system as I plan to implement it will be able to do all that I want it to do. Am I being too optimistic? Can anyone see anything I have overlooked?

 

[Donedirtcheap]

I would go 2 ga for starting loads, especially if 10 feet away. The other consideration is that if you forget and leave the switch/solenoid on, you risk killing both batteries. Read Sternwakes stuff as he has posted a ton about this issue. If you have the money for an automatic relay it would be ideal. He has posted links to it.

 

[Bdog1]

Having battery's together really requires they be the same type and the same age to charge correctly.

Seems even a manual switch would be better choice. Even a marine mechanical style on/off switch would still let you accomplish your goals.

 

[Reducto]

Wire the switch to the ignition so it will only turn on if the key is turned to the on position. That will eliminate the risk of leaving it on. If you do need to jump the car you can change it over to always on.

Fuses aren't for normal currents, they're in case something goes wrong. If that wire comes into contact with the body of the van it will do some damage - this can happen if a connector comes loose or a minor accident pushes in a body panel. I found some 80 amp fuses at Fry's in the car audio section.

 

[SternWake]

Make sure the continuous duty solenoid is rated for at least 90 amps. More is better. Trying to save a few pennies here can cost you batteries. A voltmeter on each battery on the dash will let you know if the solenoid's contacts have fused together. Solenoids passing starter current can fuse the contacts together, and then keep the batteries paralleled even with engine off.

The solenoid trigger wire can goto the blower motor circuit.

This circuit is usually deactivated during engine cranking, so that the house battery is not trying to assist starting battery. Also, any delicate electronics hooked to the house battery will not see spikes and surges from the starter motor. You can still put a switch on the trigger circuit, I recommend a lighted switch.

I would recommend fatter than 6awg cable. The vehicles voltage regulator does not really get to "see" a distant depleted house battery with thin wiring. One thing to keep in mind too is that the solenoid contacts do wear out, and will wear out faster when passing huge currents. Depleted batteries can ask for huge currents. Especially depleted AGM batteries.

You can take power for the solenoid fight from alternator(+). This makes the circuit much shorter, and allows the voltage regulator to better "see" the depleted house battery. When the VR cannot see the depleted battery well enough, it will throttle back output to the mid 13's so as to not overcharge the engine starting battery. Charge rate to depleted battery then slows to trickle

Yes this makes the alternator work harder. It will wear out faster, but could still last years. I've not replaced an alternator in 8 years, and I regularly max it out with depleted batteries. If this is to be your primary charging source, then make it as effective as possible. If the goal is maximum battery life and enough battery power for overnight, then you will sacrifice some alternator life.

Can you replace the alternator yourself if/when that time comes? Remanufactured alternators are not extremely expensive, but the quality can be hit or miss.

I've been contemplating adding a cold air intake for my alternator. It is the heat which kills them, underhood engine heat is only part of it, they generate a lot of their own heat and the more electricity they make, the more heat they make.

Charging different batteries together is not as huge a problem as some like to think. There can be issues, but basically each battery is going to take what it wants at the voltage provided. Older batteries have higher resistance and will not ask for as much as a newer battery. So as long as the voltage is not too high for either battery, well one just recharges faster than the other. It is leaving, or discharging different batteries in parallel, that is really hard on the newer better battery. if one battery is in poor condition, and the other in great condition, then the good battery is certainly at risk of overcharging on long drives. It really depends on the vehicles voltage regulator and the voltages/durations it allows, so different for each vehicle and battery set up.

I regularly charge a Northstar AGM and a flooded group31 USbattery together via the alternator. The AGM has much less resistance and is usually fully charged or nearly so when I parallel the depleted USbattery to it to share the alternator current. The AGM takes about 3% of the available current at 14.9v, the flooded battery takes the 97%.

I use 3 manual1/2/both/off switches in my system so I can use either battery for engine/house duties. Nothing Automatic. I've been trying to get further and further away from automatic systems as they limit the control I want.

Putting 2 small voltmeters on your dashboard, with the voltage sense wires directly on the battery (+) is a great way to see what is going on while you drive. Too many people put a voltmeter on an idling engine, see 14.x and think that it is always this same voltage. When you have two voltmeters , one on each battery, it shows how much and how widely the voltage swings. Watching the voltmeter when cranking the engine can help indicate when the engine battery is a bit low or undercharged. When the house battery is depleted, you will see that the engine battery is 0.2v or more higher than the depleted house battery, even though they are in parallel. When you see the voltages are the same you know the house battery is in that 80% State of charge range. When you goto start the engine in the morning, and see both batteries are at 12.0v, then you suspect the budget solenoid has fused contacts and you have been cycling both batteries inadvertently.

I really wish a shopped a little more and got red voltmeters with two decimal places.

 

[Optimistic Paranoid]

As Stern suggests, you can run TWO control wires to the solenoid, wired in parallel. One from the blower motor circuit for routine, automatic use, and a toggle switch for emergency jump starting only.

You talked about running the switch from the starting battery. What if it is completely, totally dead? It wouldn't have enough power to activate the solenoid, and your emergency jump start system would fail. For that reason, I would suggest you power the emergency jump start switch from the house batteries.

Regards
John

 

[anm]

I would go 2 ga for starting loads, especially if 10 feet away. The other consideration is that if you forget and leave the switch/solenoid on, you risk killing both batteries. Read Sternwakes stuff as he has posted a ton about this issue. If you have the money for an automatic relay it would be ideal. He has posted links to it.

I have looked into the Blue Sea ACRs, but since I would like to use it for emergency starting I would need a high amperage one (read expensive). I can do it manually cheaply. I know it's not the best solution...

---

Having battery's together really requires they be the same type and the same age to charge correctly.

Seems even a manual switch would be better choice. Even a marine mechanical style on/off switch would still let you accomplish your goals.

A manual switch IS what I'm planning to do, it will control the solenoid. The dissimilar battery types won't be an issue since this is only intended for emergency recovery.

---

Wire the switch to the ignition so it will only turn on if the key is turned to the on position. That will eliminate the risk of leaving it on. If you do need to jump the car you can change it over to always on.

Fuses aren't for normal currents, they're in case something goes wrong. If that wire comes into contact with the body of the van it will do some damage - this can happen if a connector comes loose or a minor accident pushes in a body panel. I found some 80 amp fuses at Fry's in the car audio section.

The problem with this is that I don't want to have it on whenever the van is running, just when there's an emergency and I need it on. If I wasn't planning to use the house system as an emergency jump-start battery I would fuse it. I will just have to make sure I eliminate any potential problems. Possibly I could run the 6awg wire through lengths of garden hose to provide additional abrasion resistance.

---

As Stern suggests, you can run TWO control wires to the solenoid, wired in parallel. One from the blower motor circuit for routine, automatic use, and a toggle switch for emergency jump starting only.

You talked about running the switch from the starting battery. What if it is completely, totally dead? It wouldn't have enough power to activate the solenoid, and your emergency jump start system would fail. For that reason, I would suggest you power the emergency jump start switch from the house batteries.

Regards
John

I had 'decided' to connect the solenoid coil to the starting battery because I decided it would be more likely to have a charge in it. Let's face it, the house battery is optional, the starting battery is not. Maybe I should use a spdt switch with a center off, that way I could energize the solenoid from either house or starting battery and still leave the emergency circuit off most of the time.

Maybe the two switch approach is best... I'll think about it...

 

[anm]

Make sure the continuous duty solenoid is rated for at least 90 amps. More is better. Trying to save a few pennies here can cost you batteries. A voltmeter on each battery on the dash will let you know if the solenoid's contacts have fused together. Solenoids passing starter current can fuse the contacts together, and then keep the batteries paralleled even with engine off.

The solenoid trigger wire can goto the blower motor circuit.

This circuit is usually deactivated during engine cranking, so that the house battery is not trying to assist starting battery. Also, any delicate electronics hooked to the house battery will not see spikes and surges from the starter motor. You can still put a switch on the trigger circuit, I recommend a lighted switch.

I would recommend fatter than 6awg cable. The vehicles voltage regulator does not really get to "see" a distant depleted house battery with thin wiring. One thing to keep in mind too is that the solenoid contacts do wear out, and will wear out faster when passing huge currents. Depleted batteries can ask for huge currents. Especially depleted AGM batteries.

You can take power for the solenoid fight from alternator(+). This makes the circuit much shorter, and allows the voltage regulator to better "see" the depleted house battery. When the VR cannot see the depleted battery well enough, it will throttle back output to the mid 13's so as to not overcharge the engine starting battery. Charge rate to depleted battery then slows to trickle

Yes this makes the alternator work harder. It will wear out faster, but could still last years. I've not replaced an alternator in 8 years, and I regularly max it out with depleted batteries. If this is to be your primary charging source, then make it as effective as possible. If the goal is maximum battery life and enough battery power for overnight, then you will sacrifice some alternator life.

Can you replace the alternator yourself if/when that time comes? Remanufactured alternators are not extremely expensive, but the quality can be hit or miss.

I've been contemplating adding a cold air intake for my alternator. It is the heat which kills them, underhood engine heat is only part of it, they generate a lot of their own heat and the more electricity they make, the more heat they make.

Charging different batteries together is not as huge a problem as some like to think. There can be issues, but basically each battery is going to take what it wants at the voltage provided. Older batteries have higher resistance and will not ask for as much as a newer battery. So as long as the voltage is not too high for either battery, well one just recharges faster than the other. It is leaving, or discharging different batteries in parallel, that is really hard on the newer better battery. if one battery is in poor condition, and the other in great condition, then the good battery is certainly at risk of overcharging on long drives. It really depends on the vehicles voltage regulator and the voltages/durations it allows, so different for each vehicle and battery set up.

I regularly charge a Northstar AGM and a flooded group31 USbattery together via the alternator. The AGM has much less resistance and is usually fully charged or nearly so when I parallel the depleted USbattery to it to share the alternator current. The AGM takes about 3% of the available current at 14.9v, the flooded battery takes the 97%.

I use 3 manual1/2/both/off switches in my system so I can use either battery for engine/house duties. Nothing Automatic. I've been trying to get further and further away from automatic systems as they limit the control I want.
...

@SternWake:
Maybe I should have an automatic circuit that charges both batteries when the engine runs, but with a switch so I can manually complete the circuit for jump-start duty.

If I want to be able to use the house battery as a jump-starter, should I have it connected to the alternator? Seems like connecting directly to the battery would be better. Possibly I could run a new, heavier, alternator to starting battery cable, and get the same benefit as connecting to the alternator?

Regarding automatic vs manual control, I think my mind is maturing and doesn't like to concern itself with the small details too much, so automatic would be best, or at least bright emergency lights

 

[Optimistic Paranoid]

I had 'decided' to connect the solenoid coil to the starting battery because I decided it would be more likely to have a charge in it. Let's face it, the house battery is optional, the starting battery is not. Maybe I should use a spdt switch with a center off, that way I could energize the solenoid from either house or starting battery and still leave the emergency circuit off most of the time.

Maybe the two switch approach is best... I'll think about it...

Uhh, Andrew? If the starter battery is dead, and the house batteries are so depleted that they won't energize the solenoid, how are you going to jump start the engine with them anyway?

Maybe it's just me, but I don't see the center OFF position of a SPDT switch as being as POSITIVE as the OFF position on a SPST switch. I think it would be too easy to activate it accidentally by brushing against it and not realizing you had done it.

That's assuming you go with a wire from the ignition switch or blower motor circuit for routine use, and only use the manual toggle switch for emergency jump starting.

Come to think of it, I think I would look for a push-pull switch rather than a toggle switch. Way more positive off-on.

Regards
John

 

[SternWake]

YOu are making way too much of this flip a switch emergency jumpstarter. I thought the goal was to allow the alternator to charge the house battery.

If your system is set up right, meaning all house loads moved from engine battery to house battery, there are very few instances where you will be needing to jump the engine battery. Setting this thing up solely to be able to flip a switch and parallel the batteries only for jumping the engine battery is a waste of time and money.

Carry some jumper cables instead, or a jumper pack.

Now if you are wanting to charge the house battery with the alternator, then take the power for the solenoid from the alternator. if you only goal is to waste time money and effort to wire up a flip switch jump starter then take power for solenoid from engine battery. And if you do this, well you will still be able to flip the switch and charge the house battery when alternator is running. My recommendations above were on how to most effectively get alternator amps into house battery to help get it near as fully charged as possible.

Had I known this was just for a jumpstarting I wouldn't have responded.

 

[anm]

YOu are making way too much of this flip a switch emergency jumpstarter. I thought the goal was to allow the alternator to charge the house battery.

If your system is set up right, meaning all house loads moved from engine battery to house battery, there are very few instances where you will be needing to jump the engine battery. Setting this thing up solely to be able to flip a switch and parallel the batteries only for jumping the engine battery is a waste of time and money.

Carry some jumper cables instead, or a jumper pack.

Now if you are wanting to charge the house battery with the alternator, then take the power for the solenoid from the alternator. if you only goal is to waste time money and effort to wire up a flip switch jump starter then take power for solenoid from engine battery. And if you do this, well you will still be able to flip the switch and charge the house battery when alternator is running. My recommendations above were on how to most effectively get alternator amps into house battery to help get it near as fully charged as possible.

Had I known this was just for a jumpstarting I wouldn't have responded.

No this is NOT just for jump starting! I have two goals:

1. To be able to charge the house battery off the alternator, but only if it has been so depleted that the solar panels can't bring it back soon enough.
2. To allow jump-starting in an emergency.

If I'm connecting the two systems together it seems a shame to not allow jump-starting.

---

Uhh, Andrew? If the starter battery is dead, and the house batteries are so depleted that they won't energize the solenoid, how are you going to jump start the engine with them anyway?

Maybe it's just me, but I don't see the center OFF position of a SPDT switch as being as POSITIVE as the OFF position on a SPST switch. I think it would be too easy to activate it accidentally by brushing against it and not realizing you had done it.

That's assuming you go with a wire from the ignition switch or blower motor circuit for routine use, and only use the manual toggle switch for emergency jump starting.

Come to think of it, I think I would look for a push-pull switch rather than a toggle switch. Way more positive off-on.

Regards
John

If I'm out in the boonies, both batteries severely depleted, and a bear ate my cell phone, I'm going to have to let nature take its course and charge the house battery. Then I'm still going to have to jump-start the van. If I can connect the two systems together (via the solenoid - which is required for charging the house battery from the alternator) I stand a chance of getting some of the excess solar into the starting battery, and being able to jump-start the van...

There are many-many ways to do it, I prefer easy (meaning simple user operation, like flipping a toggle switch) and reliable. And SternWake's idea of indicator lights also makes sense...

 

[ccbreder]

The argument against a switch for jump starting from house bank is mainly the size of the wire/solenoid circuit to accomplish this. Starter will draw hundreds of amps. You would need all that extra expense when all you need is a set of jumpers.

 

[SternWake]

The solenoid will consume .5 to .8 of your solar amps when you decide to allow solar current into engine battery.

Latching solenoids would be a better choice as they only need a momentary burst of 12vdc to engage or disengage. but require a momentary switch and the indicator light is that much more important.

Also unless the solar already has the batteries at ABSvoltage, then you want the alternator to assist house battery charging. Always.

It takes time at absv to get the battery to full charge, and higher alternator amps help get there earlier in the day. Quit worrying about wasting solar wattage. Your batteries are happiest when the charge controller gets to bleed off some extra solar wattage. Practice OCD elsewhere.

it is more important to ensure getting to that elusive 100% recharge than it is to not waste a single solar electron.

One will always read how low and slow trickle charging is always best for a battery. This is not true, especially when the next discharge cycle begins late afternoon.

My experiences with this lifestyle says the battery very much appreciates high amperage alternator blasts in the morning with solar taking over the rest of the day. It behaves much better than if solar alone recharged the bank lower and slower and" fully" by late afternoon. You cannot really believe full charge indicators on any charging source. None of them actually test the battery, they just follow the algorithm and flash the full charge light if the algorithm is met. And the algorithm is designed to not overcharge, which means intentionally undercharge.

Some higher end AGMS absolutely need high amperages when depleted, like 40 amps minimum for every hundred amp hours of storage. Lifeline AGM says as much amperage as you can muster. Odysseys say no less than 40amps per 100AH when deeply cycled. The deeper the cycle the more important it is to meet these minimums and as soon as possible.

lesser AGMS will say to not exceed 30 per 100. With just 6awg, you will not exceed 30 amps for long anyway so it is of little/no concern.

If you do need this jumpstarter method, flip the switch a few minutes before cranking the starter. It will help conserve the solenoids contacts. They are most likely to fuse together passing starter current. Unless you have a voltmeter on each battery, or actually bust out the DMM each engine shut down, you will never know when the contacts fuse together, until you go to start the engine and get the dreaded click. The cheaper the solenoid, the quicker the contacts will fuse together so quality and high continuous ratings are important when making this purchase.

Save money elsewhere.

 

[anm]

The argument against a switch for jump starting from house bank is mainly the size of the wire/solenoid circuit to accomplish this. Starter will draw hundreds of amps. You would need all that extra expense when all you need is a set of jumpers.

I understand what you're saying, and I'll think about it...

 

[Lucky mike]

Let me see........100 dollars worth of materials and an hour or 2 to put them in......or a nice set of 12 or 16 ' jumper cables to do the same work not to mention if it doesnt work with the switch your going to need the cables to get a jump start..........


I think I will grab a 12 pack and sit back with my cables and watch you do this.......then charge you for the jump start because you have alot of money.....of course I will refund it if you let me watch you wrestle the bear that ate your cell phone!!!!

 

[anm]

Let me see........100 dollars worth of materials and an hour or 2 to put them in......or a nice set of 12 or 16 ' jumper cables to do the same work not to mention if it doesnt work with the switch your going to need the cables to get a jump start..........


I think I will grab a 12 pack and sit back with my cables and watch you do this.......then charge you for the jump start because you have alot of money.....of course I will refund it if you let me watch you wrestle the bear that ate your cell phone!!!!

All I need to buy is a solenoid, switch, and indicator lights, I already have the rest of it in my junk box, I figure $30...

Since I'll already have it done, I'll start my van, chase the bear down and get my phone back, and then sit down and have one of your beers...

 

[Optimistic Paranoid]

All I need to buy is a solenoid, switch, and indicator lights, I already have the rest of it in my junk box, I figure $30...

Question for you. How long do you plan to keep this vehicle?

I see Amazon has a nice 200 amp solenoid for $45 and a really nice 500 amp solenoid is $75.

I suspect that a decade from now, the overbuilt 500 amp solenoid will still be working fine, and you'll be able to move it to your next vehicle.

I wonder how many $20 solenoids you're going to burn through in the next 10 years?

Anyway, it's your van, your finances, and your life. The only person you need to keep happy is yourself. Good luck with whichever way you do it.

Just remember, some of us will still be around to say "I Told You So!" <grin>

Regards
John

 

[anm]

Question for you. How long do you plan to keep this vehicle?

I see Amazon has a nice 200 amp solenoid for $45 and a really nice 500 amp solenoid is $75.

I suspect that a decade from now, the overbuilt 500 amp solenoid will still be working fine, and you'll be able to move it to your next vehicle.

I wonder how many $20 solenoids you're going to burn through in the next 10 years?

Anyway, it's your van, your finances, and your life. The only person you need to keep happy is yourself. Good luck with whichever way you do it.

Just remember, some of us will still be around to say "I Told You So!" <grin>

Regards
John

Now John, I thought you were the Optimistic Paranoid!

My finances dictate that I do it as inexpensively as possible while still achieving the functionality I need, if I can't do that it doesn't get done...

 

[freenez2]

I use one of these...

http://www.batteryminders.com/batte...arger-maintainer-desulfator-world-wide-usage/

I plug it into the inverter which is powered from the house batteries. The other end goes into the power point on the dash. Nothing to it. The house batteries are charged by solar. When parked for long periods of time, I charge the starter battery every few days to keep it topped off.

 

[anm]

I use one of these...

http://www.batteryminders.com/batte...arger-maintainer-desulfator-world-wide-usage/

I plug it into the inverter which is powered from the house batteries. The other end goes into the power point on the dash. Nothing to it. The house batteries are charged by solar. When parked for long periods of time, I charge the starter battery every few days to keep it topped off.

That is another option, I have a small smart charger that I should bring with me...