How to make a cheap isolated dual-battery setup for $50
- Thread starter evldave
- Start date
dlichterman
Explorer
Your question is a little confusing. Are you talking about the factory installed 12V?
I wired in a second set of 12V outlets that run off the aux battery so I have an always on 12V source inside the cab.
dlichterman
Explorer
You would need to re-wire them. Might be better off just adding some.
(Personally I run a dumb solenoid in my truck, as described in this thread - but I'm just a lowly journeyman electrician who put in 24,000 hours in the trade before I moved on to another career (designing and building computer networks) - so what do I know?)
Thanks for the chuckle, and the info, and the thread.
Eurovan2003
New member
I am new to this but have a question. With setup on page one of this thread, using a solar panel, dual battery, and instead of an isolation solenoid, using a relay triggered by the alternator trigger voltage (that is how my vehicle came originally) to keep the aux battery isolated. I am wondering if there is any problem with the solar controller competing with the alternator regulator to control the voltage, and thus causing any damage with either? Thanks for any advise.
4RunAmok
Explorer
The solar charge controller (make sure you're using a good one, like Morningstar SunSaver) should be "intelligent" enough to sense the voltage coming in from the other side of the system and react accordingly. There is nothing special about my solar install. The SunSaver battery leads, connect directly to my Blue Sea Fuse Block, (-) to a ground post, and the (+) to one of the fused slots, with a 10 amp fuse.
Kevin.Hutch
New member
VSR beats old tech solenoids hand down.
There is no problem with a Voltage Sensing Relay if the charge source is coming from both sides, the lower charged battery will absorb the most charge (lower internal resistance) until both are equally charged, then the regulator/s will control the charge rate based on the voltage they see. No two regulators are identical, so one becomes the dominant controller.
The only down side with a VSR is it does consume current when in idle, good ones well under 10 milliamp and most should be isolated if long periods with no charge source is required.
The VSR on standby just switches on when the sense voltage reaches the pre-set value (around 13.5) indicating the charge source is present and connects both batteries in parallel and switches off at the pre-set value (around 12.5) when the charge source is removed.
Most older VSR's did not sense both sides, not expecting to see two charge sources, but most new ones do, allowing the starter battery charge source or the auxiliary (house) battery charge source (solar and/or mains charger) to initiate the charging. You just need to see on a bright sunny day (with the alternator off) if the indicator shows the VSR is on, or if no indicator, both battery voltages are the same will tell what you have. If you run the motor in the daylight then switch it off the solar should keep the VSR on either way.
The new generation of solar charge controllers incorporate both the function of regulation and VSR.
Many new ones often called DC/DC convertors combine the MPPT (MultiPoint Power Tracking) function (which is simply a switch mode variable voltage input regulator) to both the solar, mains charger and alternator inputs and also include the VSR function and their price is tumbling, at less than half what they were a year ago.
Kevin H
There is no problem with a Voltage Sensing Relay if the charge source is coming from both sides, the lower charged battery will absorb the most charge (lower internal resistance) until both are equally charged, then the regulator/s will control the charge rate based on the voltage they see. No two regulators are identical, so one becomes the dominant controller.
The only down side with a VSR is it does consume current when in idle, good ones well under 10 milliamp and most should be isolated if long periods with no charge source is required.
The VSR on standby just switches on when the sense voltage reaches the pre-set value (around 13.5) indicating the charge source is present and connects both batteries in parallel and switches off at the pre-set value (around 12.5) when the charge source is removed.
Most older VSR's did not sense both sides, not expecting to see two charge sources, but most new ones do, allowing the starter battery charge source or the auxiliary (house) battery charge source (solar and/or mains charger) to initiate the charging. You just need to see on a bright sunny day (with the alternator off) if the indicator shows the VSR is on, or if no indicator, both battery voltages are the same will tell what you have. If you run the motor in the daylight then switch it off the solar should keep the VSR on either way.
The new generation of solar charge controllers incorporate both the function of regulation and VSR.
Many new ones often called DC/DC convertors combine the MPPT (MultiPoint Power Tracking) function (which is simply a switch mode variable voltage input regulator) to both the solar, mains charger and alternator inputs and also include the VSR function and their price is tumbling, at less than half what they were a year ago.
Kevin H
Eurovan2003
New member
Kevin and Mitch
Thanks for the reply. My vehicle is a 2003 and has a separate wire from the alternator to turn on the relay. I was concerned about blowing either the regulator or MPPT, thanks for the confidence that that is not an issue.
I have an additional question- I understand you should not disconnect either the solar panel while a load is on it- other than covering the solar panel (impractical) what is a way to properly disconnect the solar from the circuit if you should need to do so. Also , what happens if you do that they advise against it, I did see the note on it destroying switch contacts. Wouldn't a small capacitor across the switch stop that?
This is a very helpful thread. A lot of good information.
Thanks for the reply. My vehicle is a 2003 and has a separate wire from the alternator to turn on the relay. I was concerned about blowing either the regulator or MPPT, thanks for the confidence that that is not an issue.
I have an additional question- I understand you should not disconnect either the solar panel while a load is on it- other than covering the solar panel (impractical) what is a way to properly disconnect the solar from the circuit if you should need to do so. Also , what happens if you do that they advise against it, I did see the note on it destroying switch contacts. Wouldn't a small capacitor across the switch stop that?
This is a very helpful thread. A lot of good information.
Kevin.Hutch
New member
Panel disconecting
It is good practice to remove the load from any power source before disconnecting it.
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DC can easily drag an large arc when disconnected (compared to AC) and arcs can blind, weld or create significant spikes that can cause component failure.
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This is why most switches have a 10% factor for DC (ie 240 volt AC switch is usually only rated for 24 volts DC).
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Disconnect speed and arc suppression is important when switching and yes a capacitor could help absorb a spike just as there are other non mechanical components that can be used to switch, in fact a voltage regulator typically switches on/off to provide regulation (PWM is Pulse, "on/off", Width "time" Modulation).
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It is not usual to have a switch between a low voltage panel and the regulator, so covering the panel is the best way of disconnecting a panel or disconnect in the shade or at night. Why would you need to disconnect normally anyway?
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Kevin H
It is good practice to remove the load from any power source before disconnecting it.
.
DC can easily drag an large arc when disconnected (compared to AC) and arcs can blind, weld or create significant spikes that can cause component failure.
.
This is why most switches have a 10% factor for DC (ie 240 volt AC switch is usually only rated for 24 volts DC).
.
Disconnect speed and arc suppression is important when switching and yes a capacitor could help absorb a spike just as there are other non mechanical components that can be used to switch, in fact a voltage regulator typically switches on/off to provide regulation (PWM is Pulse, "on/off", Width "time" Modulation).
.
It is not usual to have a switch between a low voltage panel and the regulator, so covering the panel is the best way of disconnecting a panel or disconnect in the shade or at night. Why would you need to disconnect normally anyway?
.
Kevin H
Stitebunny
Adventurer
A question regarding the original solenoid plan and jump starting.
How large of a solenoid do you need to be able to handle the current of jump starting?
And with that, what size fuse or breaker at the battery as well?
I will have about an 8 foot run from the leisure battery to the starter battery and want to make sure I have a solenoid up to the task and the battery properly protected.
How large of a solenoid do you need to be able to handle the current of jump starting?
And with that, what size fuse or breaker at the battery as well?
I will have about an 8 foot run from the leisure battery to the starter battery and want to make sure I have a solenoid up to the task and the battery properly protected.
dlichterman
Explorer
I have no idea what I'm doing, but I accidentally left 100W of lighting on for hours and drained my battery enough to get the dreaded "click" when trying to start. Had enough power to join the batteries with the solenoid and self jump though. I used a 200A solenoid with 200A fuses:
http://amzn.com/B000CEBXRS
http://amzn.com/B005EUTLYW
http://amzn.com/B00CBB72AM
So far I haven't burnt the truck down.....
dwh
Tail-End Charlie
I've jumped my Ford 460 several times through my truck's split-charge relay which uses a decent quality 80a rated solenoid. Most starters are rated at like 250a max draw but actually only draw around 150a or less. So if you rig for 200a you'll be fine.
dwh
Tail-End Charlie
Multiple different charging systems don't affect each other. They're too dumb. Each just supplies current until the voltage reaches a certain point and then shuts off. They don't compete, their effect is added together and each contributes something to the total. Say 20a from the alternator and 10a from the solar - total power available = 30a.
So say your alternator's voltage regulator is set to 14.2v and your solar charge controller is set to 14.4v. Below 14.2v, they'll both be supplying power. Between 14.2v and 14.4v the alternator will be shut off but the solar will still be supplying power until the voltage reaches 14.4v and then the solar charge controller will shut off.
If the solar could supply enough power to hold the voltage up over 14.2v, then the chassis voltage regulator wouldn't ever turn the alternator on.
The battery can supply hundreds of amps, and the various chargers are, of course, protected from any backflow from that BigAss(tm) battery. So whatever amps this charger or that charger is supplying, isn't going to overcome the other chargers' backfeed protection and damage them.