wrcsixeight,
For those of us who are trying (perhaps unsuccessfully to follow this thread) is this the portion of the response that you are referring to when you say that you are concerned about welding the contacts?
thanks.
cheap and simple dual battery set-up
- Thread starter zuknewbie
- Start date
For those of us who are trying (perhaps unsuccessfully to follow this thread) is this the portion of the response that you are referring to when you say that you are concerned about welding the contacts?
thanks.
dwh
Tail-End Charlie
Not really.
What he's concerned about is feeding the amps from the aux battery to the starter, THROUGH the solenoid. That heavy load could (possibly, potentially, theoretically) weld the internal contacts together.
That is, it could weld the contacts that connect the two large terminals together when the electromagnet is energized by putting 12v through the small terminals.
It really makes no difference *how* the small terminals get energized - whether by turning on the key, or using the jumper I described - the big amps will flow from one big terminal to the other big terminal across the internal contacts.
It's a valid point - though I've never seen it happen or heard of anyone who had it happen, that doesn't mean it *won't* happen. Then again, they do make those same solenoids in various sizes. So if one were worried about welding the contacts on an 80a unit, it wouldn't cost much more to go up to a 200a unit.
What I described, was simply a hack to get power from the aux battery to energize the solenoid in the event that the main battery is too dead to energize the solenoid.
For instance, if you wired a solenoid to get power when the key is turned on. That power comes from the main battery. When it's dead - you turn the key on, but the solenoid doesn't energize.
If the aux battery has some juice in it, then that power will be present at the large terminal on the solenoid - because is has a big cable to the aux battery.
So you could jumper power from that point (aux battery large terminal on the solenoid) to the small terminal on the solenoid that energizes the electromagnet.
That would energize the solenoid to get power to the other big terminal (the main battery side).
The problem with that hack - energizing the solenoid with power from the aux battery - is that the main battery is dead, so ALL the power to feed the starter now comes from the aux battery...though the solenoid's internal contacts.
That is pretty much the definition of "worst case scenario".
So...it's a hack. No doubt. But it's a hack that could save your butt.
There are two ways to mitigate the (possible, potential, theoretical) problem:
A) Use jumper cables.
B) Wait a while for some power to cross over to the main battery, so that the full amps for the starter doesn't all come from the aux battery.
wrcsixeight
Adventurer
I have a friend with a '78 p30 Chevy that had 2 auxiliary marine batteries. The engine battery had a fair sized parasitic draw and would last no more than a week, but he was unconcerned as he'd just jumper the solenoid from the good batteries and run the starter from the good aux batteries.
After about 10 episodes of doing this, he could not start the vehicle.
A voltmeter indicated all three batteries were at 9.42 volts.
The Solenoid had failed, the contacts had fused, and all the batteries were always in parallel.
All three batteries, even after fully charging, had very little capacity left, so in addition to a new higher rated solenoid, he bought 3 new batteries, and finally decided to find the parasitic draw.
Granted this is an extreme example, but shows it is possible, however unlikely.
After about 10 episodes of doing this, he could not start the vehicle.
A voltmeter indicated all three batteries were at 9.42 volts.
The Solenoid had failed, the contacts had fused, and all the batteries were always in parallel.
All three batteries, even after fully charging, had very little capacity left, so in addition to a new higher rated solenoid, he bought 3 new batteries, and finally decided to find the parasitic draw.
Granted this is an extreme example, but shows it is possible, however unlikely.
dwh
Tail-End Charlie
Yes, a manual switch will work. But I use my rig a lot and no way would I want to have to deal with that switch on a daily basis (or a many times a day basis).
There are reasons for using a manual switch, but I certainly would not choose to go with a manual switch just to prevent the off chance of theoretically welding the contacts of a winch/golf cart type solenoid during the rare times (once or twice a year) that I've had to jump start the truck off the aux battery. I've jumped the 460 through the solenoid a few times and had 0 issues.
The truck is a Ford, which has an external starter relay, which is basically the same as the solenoids that we're talking about here, except it's not rated for continuous use. But there is no doubt that it can handle the starter current. I carry a spare starter solenoid in the parts box anyway, so if the battery solenoid did happen to fail out in the field, I could easily swap in the starter relay an run with it until I got to town and got a replacement battery solenoid.
I've known guys who've used Ford starter solenoids as battery isolators for years without having them fail, so even though they aren't 'technically' for continuous use (like a winch/golf cart solenoid), anecdotal evidence shows they seem to handle it just fine.
I suppose, to be really top notch, hot ********, high speed, low drag, full race, Professional (with a capital P ), Custom (with a capital C ), it would be pretty simple to rig a winch/golf cart solenoid powered off the main battery (engine run circuit) for day-to-day battery isolator use, and also parallel a starter solenoid next to it with a (momentary) switch to energize if off the aux battery.
Then if a self-jump was needed, one could just push the button to energize the starter solenoid to tie the batteries and start the truck - and no worries about welding the contacts in a starter solenoid.
Might as well also rig that switch to cut power to the battery solenoid at the same time so no current can possibly go through it.
But again, if someone were really worried about burning up their isolator solenoid during those rare times when they need to jump start the truck off the aux battery, there is a simple way to protect the solenoid - use jumper cables.
(BTW, anyone looking to use a switch should be aware that there are two types; "Make before break", and "break before make". Make before break is generally preferred for RV/Marine use, since you can switch between batteries without losing power to the loads.)
There are reasons for using a manual switch, but I certainly would not choose to go with a manual switch just to prevent the off chance of theoretically welding the contacts of a winch/golf cart type solenoid during the rare times (once or twice a year) that I've had to jump start the truck off the aux battery. I've jumped the 460 through the solenoid a few times and had 0 issues.
The truck is a Ford, which has an external starter relay, which is basically the same as the solenoids that we're talking about here, except it's not rated for continuous use. But there is no doubt that it can handle the starter current. I carry a spare starter solenoid in the parts box anyway, so if the battery solenoid did happen to fail out in the field, I could easily swap in the starter relay an run with it until I got to town and got a replacement battery solenoid.
I've known guys who've used Ford starter solenoids as battery isolators for years without having them fail, so even though they aren't 'technically' for continuous use (like a winch/golf cart solenoid), anecdotal evidence shows they seem to handle it just fine.
I suppose, to be really top notch, hot ********, high speed, low drag, full race, Professional (with a capital P
), Custom (with a capital C ), it would be pretty simple to rig a winch/golf cart solenoid powered off the main battery (engine run circuit) for day-to-day battery isolator use, and also parallel a starter solenoid next to it with a (momentary) switch to energize if off the aux battery.Then if a self-jump was needed, one could just push the button to energize the starter solenoid to tie the batteries and start the truck - and no worries about welding the contacts in a starter solenoid.
Might as well also rig that switch to cut power to the battery solenoid at the same time so no current can possibly go through it.
But again, if someone were really worried about burning up their isolator solenoid during those rare times when they need to jump start the truck off the aux battery, there is a simple way to protect the solenoid - use jumper cables.
(BTW, anyone looking to use a switch should be aware that there are two types; "Make before break", and "break before make". Make before break is generally preferred for RV/Marine use, since you can switch between batteries without losing power to the loads.)
Scoutn79
Adventurer
When I did my dual battery system the plan was to have the primary battery do nothing but turn the starter. The second battery (chassis) controls the FI (fuel injection) and everything else...Stereo, lights, winch, Radio, Engel etc. My concerns was that I didn't want a system that would automatically connect the batteries when the ignition was turned on to play the stereo...defeats the purpose of two systems if they can be connected when the alternator isn't charging/engine running.
BTW the IBS relay uses .3 amps to connect and the typical big metal start relays from auto parts stores use about 3.5 amps to connect. I use the IBS relay from Sierre Expeditions.
I ended up using a low pressure electric fuel pump control switch (3-5 psi) that threads into a port in the oil galley hole in the block (normally open) to control the connector/charge relay.
The start battery and alt charge lead connect to one post of the 200 amp continuous duty (500 amp intermittent) relay and the chassis battery and various other wires as required connect to the other terminal. The relay I used requires both hot and ground leads to operate...It isn't a grounded relay...I ran a jumper from the start battery post on the relay to the hot lead on the relay and then a ground lead to the oil pressure switch and grounded the other end to a nearby bolt...This way I don't have a hot lead running down along the side of the hot engine block. This uses the ground as the control.
IF and WHEN I draw the chassis battery down so low it won't run the fuel pump there are several ways to get the FI online to start the engine.
1) Jumper cables from one batt to the other.
2) a small jumper wire with alligator clips to connect the two batt terminals on the relay ( I tested this idea with a 16 GA wire to see if it would work with such a small wire and it does)
3) manually ground the wire running to the oil pressure switch
4) put in a separate on/off switch to control an aux lead on the ground side of the relay control...essentially to manually ground the oil pressure switch wiring to connect the relay....This can be mounted anywhere you like...Like on the dash so you don't even have to get out of the truck to connect the relay if the weather is really bad, this would be nice. I would use a momentary switch in the cab and a non momentary if the switch was in the engine compartment...just don't forget to turn it off and make sure it can't be accidentally bumped and turned on.
Simple, inexpensive, easy to trouble shoot and repair if needed, and extremely reliable.
For my use being able to turn the engine over is the single most important electrical concern and highest amp draw other than the winch...everything else can be done with out. Since the FI uses such a low amp draw it can still work with an almost dead battery so..at least for now I am fine leaving this system wired as is.
This was done on a IH Scout so the wiring isn't as complex as a new vehicle but the principal is the same on anything.
HTH
Darrell
BTW the IBS relay uses .3 amps to connect and the typical big metal start relays from auto parts stores use about 3.5 amps to connect. I use the IBS relay from Sierre Expeditions.
I ended up using a low pressure electric fuel pump control switch (3-5 psi) that threads into a port in the oil galley hole in the block (normally open) to control the connector/charge relay.
The start battery and alt charge lead connect to one post of the 200 amp continuous duty (500 amp intermittent) relay and the chassis battery and various other wires as required connect to the other terminal. The relay I used requires both hot and ground leads to operate...It isn't a grounded relay...I ran a jumper from the start battery post on the relay to the hot lead on the relay and then a ground lead to the oil pressure switch and grounded the other end to a nearby bolt...This way I don't have a hot lead running down along the side of the hot engine block. This uses the ground as the control.
IF and WHEN I draw the chassis battery down so low it won't run the fuel pump there are several ways to get the FI online to start the engine.
1) Jumper cables from one batt to the other.
2) a small jumper wire with alligator clips to connect the two batt terminals on the relay ( I tested this idea with a 16 GA wire to see if it would work with such a small wire and it does)
3) manually ground the wire running to the oil pressure switch
4) put in a separate on/off switch to control an aux lead on the ground side of the relay control...essentially to manually ground the oil pressure switch wiring to connect the relay....This can be mounted anywhere you like...Like on the dash so you don't even have to get out of the truck to connect the relay if the weather is really bad, this would be nice. I would use a momentary switch in the cab and a non momentary if the switch was in the engine compartment...just don't forget to turn it off and make sure it can't be accidentally bumped and turned on.
Simple, inexpensive, easy to trouble shoot and repair if needed, and extremely reliable.
For my use being able to turn the engine over is the single most important electrical concern and highest amp draw other than the winch...everything else can be done with out. Since the FI uses such a low amp draw it can still work with an almost dead battery so..at least for now I am fine leaving this system wired as is.
This was done on a IH Scout so the wiring isn't as complex as a new vehicle but the principal is the same on anything.
HTH
Darrell
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