Dual Battery questions

[Hants]

I'm in the planning stages of adding dual batteries to my LX450 princess: ). I've done a bunch of research here on MUD as well as other forums. I've also studied several books and FAQ's on 12v systems (boats, RV's, autos).

I did well in high-school electronics, but that was a long time and a lot of martinis ago

As I progress, I'll do a complete writeup (my 1st) for the forum.

At this point, I have a few questions:

1. Why do so many (automatic) isolators operate based on voltage (rather than Alternator Good)? I would think that drawing down the primary battery while the Aternator is charging would not be a big problem (as soon as the draw drops, the alternator would be charging the batteries again -- and very low SOC batteries charge quickly).

2. Why would one want (automatic) isolation under heavy draw (e.g. winching)? It seems that this would dramatically reduce the power (Watts) available to the winch.

In my feeble mind, it seems that voltage based isolation (e.g. BlueSea ACR) would cause cycling. Draw starts, voltage at each battery drops to (say) 11V, isolator separates batteries, primary battery jumps back to (say) 12.7V and secondary battery drops to (say) 10.5V, isolator parallels batteries because primary is high, voltage drops due to load, isolater separates batters, ad nauseum. It seems that would be mitigated somewhat (but not completely) by the alternator charging (which would raise the current threshold to X + (say) 80A.

3. What is the distinction between a solenoid and a relay? I’ve only seen relays up to 30A, but solenoids up to 200A (continuous). They certainly look different externally, but what is the electrical difference?

4. Is there an auto-resetting type of switch? For instance, push button to close circuit (in this case to trigger the solenoid for manual-parallel). Circuit stays closed until an external trigger (for instance Alternator Good), at which time the switched circuit automatically opens?

 

[MrMoMo]

You want isolation so you can only kill one battery, and not leave yourself stranded by having two dead batteries.

A solenoid is basically the same as a relay.

You might want to go with the old fashioned diode type isolator, they don't close and open circuits, they only prevent current from travelling from one battery to another. I would suggest a Surepower with one A post and 2 B posts. Depending on the size of your alternator, a 702 for a 70A alt max, 1202 for a 120A alt max, all the way up to a 3002, for a 300A alternator.

The only real disadvantage to this type of isolator, is the small voltage drop across it. However, I would not be concerned about this for your application.

I don't work for surepower by the way... but I do use their products in the electrical systems I design for the Fire/Rescue boats where I work.

You can also install a paralelling solenoid, or switch, to give you that extra juice of having two batteries in paralell for when you are winching.

Connect your negative posts together permanently, and use a heavy duty switch (like a blue sea on/off battery switch) or a continuous duty solenoid to connect positive to positve.

You could even get really fancy, and use your winch control to trigger the paralelling solenoid, so it would only paralell while the winch was under power.

You could get even fancier by using your paralelling solenoid to connect your batteries in series, and run a 24V winch. (technically, it would be a "series-ing" solenoid)

For an automatic switch, you could use a shotkey diode to monitor voltage, powering a relay or solenoid. When the voltage goes above (or below) a pre-determined voltage, depending on your configuration the circuit would open (or close). Wire this in series with a dash mounted switch, so you have an "and" circuit. This means, "if" you close your pushbutton switch "and" your voltage sensing diode is within range then your relay/solenoid would close (or open). When the voltage drops (or rises) it would open (or close)

Much simpler way to do all this, use the Blue Sea ACR, you can manually control it (electrically)

Did that confuse you enough?

 

[Rich]

...1. Why do so many (automatic) isolators operate based on voltage (rather than Alternator Good)?...

2. Why would one want (automatic) isolation under heavy draw (e.g. winching)?...

3. What is the distinction between a solenoid and a relay? I’ve only seen relays up to 30A, but solenoids up to 200A (continuous). They certainly look different externally, but what is the electrical difference?...

1) "Alternator good" signal is not universally available, so isolator manufacturers don't rely on it being there. Additonally, voltage is an indicator of battery state of charge, which in can be more meaningful than just whether or not alternator is outputting current. So being battery voltage aware can enable an automatic device to be a bit more intelligent, which may or may not suit your objectives.

2) Most battery isolators, including many or all of the most expensive "all electronic" isolator / combiners can not handle the full draw of an electric winch, so automatic disablement of the paralleling device may prevent the inadvertent destruction of the isolator. Check out the max amperage capability of the different isolators. A winch can draw over 400 amps.

As previously mentioned, it also can prevent the inadvertent total discharge of both batteries during winching.

3) In the context of automotive electrical systems, relay and solenoid are essentially synonymous.

 

[Hants]

You want isolation so you can only kill one battery, and not leave yourself stranded by having two dead batteries.

I concur with auxiliary loads (e.g. fridge, inverter, winch) AND with the engine off.
It seems to me, though, that with the engine on (Alternator Good), that the batteries would be quickly re-charged to above "dead" (due to high-amperage acceptance by a battery with a very low SOC).
Even with a winch drawing more than the alternator can output and more than the batteries (in parallel) can maintain without significantly dropping voltage, I'm thinking that the risk of dead batteries ("can't start the engine") is very low (as long as you leave the engine on for a period of time to pump some juice back into them).
Am I all wet here?

You might want to go with the old fashioned diode type isolator, they don't close and open circuits, they only prevent current from travelling from one battery to another.

My understanding (I haven't specifically looked) is that the stock Alternator does NOT provide an external voltage sense wire (to attach post-isolator). Consequently, the voltage at the the battery very likely would be too low to fully charge the batteries (ever or in a very long time).

You can also install a paralelling solenoid, or switch, to give you that extra juice of having two batteries in paralell for when you are winching.
Connect your negative posts together permanently, and use a heavy duty switch (like a blue sea on/off battery switch) or a continuous duty solenoid to connect positive to positve.

This is similar to what I'm planning. Specifically, my plan is to use a constant-duty high-amp solenoid, and activate it via the Alternator Good signal.
The reason for this thread is to get my head wrapped around some of the other "features" that others include in their systems.

You could even get really fancy, and use your winch control to trigger the paralelling solenoid, so it would only paralell while the winch was under power.

I hadn't considered that one.... my concern would be draining the primary battery when winching with the engine off. Automatic transmission & dead battery = long walk home.

You could get even fancier by using your paralelling solenoid to connect your batteries in series, and run a 24V winch. (technically, it would be a "series-ing" solenoid)

I don't understand how this would work? My limited understanding of parallel vs series connection of batteries indicates that one would need to switch both the positive AND negative lines around to get 24V. How could you do this with a single solenoid? How would you keep from cooking all of your 12V accessories (including the ECU)?

...you could use a shotkey diode to monitor voltage...

Woah... I'm not up to RT's skill level with electronics....

 

[Niner]

An automatic isolator does just that. isolates. so you may run you aux battery dead if you wish to, and not touch the main start run battery. Once the vehicle is running it will allow the alternator to charge both batterys, without allowing the dead battery to draw juice from the start run battery.

 

[Hants]

1) "Alternator good" signal is not universally available, so isolator manufacturers don't rely on it being there.

Makes sense.

which may or may not suit your objectives.

It doesn't at this time... but I reserve the right to change my objectives!

Most battery isolators, including many or all of the most expensive "all electronic" isolator / combiners can not handle the full draw of an electric winch, so automatic disablement of the paralleling device may prevent the inadvertent destruction of the isolator. Check out the max amperage capability of the different isolators. A winch can draw over 400 amps.

Makes sense. It brings up another question, though:
Winch draw = 400A (plus or minus)
Alternator output = 80A (plus or minus) at 14V (plus or minus)
Batteries each output up to (say) 300A at 11V (plus or minus)
250A constant-duty solenoid parallels system with 1/0 cables (375A intermittent)
Winch is connected to the "auxiliary" side of the solenoid
Engine is on and Alternator is charging. Consequently, solenoid is paralleling system. Winch is operating at near-stall (400A draw).
My understanding is the following:
Alternator provides first 80A because it is higher voltage than the batteries.
Batteries would each provide 160A (assuming identical batteries and identical SOC).
System voltage would be around 11V.
Amperage through the solenoid would be 240A (rated for 375A for 5 minutes).
If the Auxiliary battery were severly discharged prior to winching, primary battery would provide (say) 240A, and the auxiliary battery would provide (say) 80A. System voltage would be around (say) 10V. In this case, amperage through the solenoid would be 320A.
Is my thinking correct?

 

[mobi-arc]

Blue Sea ACR will cycle constantly, meaning usually several times a minute. Every time it cycles on and off, the contacts arc and the resistance through the device increases. Eventually the resistance is so high and it gets so hot that it fails....it's a mechanical solenoid. Traditional isolators like Surepower have TREMENDOUS voltage drops and, by nature of the their design, will not allow a battery to completely charge. They get hot due to the innefficiency, thus the 8 pound aluminum finned designed which is supposed to be mounted to vertically. True that most isolators can't handle whiching current. Some can, you just have to find them and be willing to pay a premium price for a premium product. If you're cost sensitive, be prepared to trade performance and reliability.

 

[Mike S]

Blue Sea ACR will cycle constantly, meaning usually several times a minute. Every time it cycles on and off, the contacts arc and the resistance through the device increases. Eventually the resistance is so high and it gets so hot that it fails....it's a mechanical solenoid.

This is NOT my experience. I installed and ran a BlueSea ACR for over a year under a lot of conditions... here is what I know...

The ACR is normally combined. It opens (isolates) only under manual control or when the voltage on either the primary or secondary (acc) battery drops below the preset voltage limit. This prevents the draining of the primary battery.

The ACR does not then combine the batteries until the primary has reached full charge. It then combines the batteries for the secondary battery to be charged.

According to reports cycling is rare, and I never experienced it. According to BlueSea specs, " Internal time delay prevents relay action for transient conditions, voltage must be within range for approximately one minute to cause closure, relay will open when overvoltage is detected for approximately 15 seconds. Meets SAE J1171 - External ignition protection requirements."

Proper installation allows three modes of operation - manually combined, Auto, or manually isolated. This means that if you want to winch, you can manually isolate the secondary (winch) battery from the dash, then operate the winch. When done, you can return to auto mode, and the alt will check the charge on the primary battery, then combine to begin recharging the secondary battery.

This is a robust system used for marine applications. It will limit voltage as a protection for the system wiring.

I do not work for or own stock in the company - just happen to like marine grade products designed for heavy duty marine applications.

M

 

[mobi-arc]

To each their own.

Fact: Solenoids are moving parts that are guaranteed to fail.
Fact: A solenoid's best performance occurs day one. Each time it subsequently opens and closes, it arcs increasing the devices resistance ever so slightly.

Perhaps I'm different, but if I could but a Toyota with no moving parts, I'd be all over it. If I were to buy an isolation device, and I had a choice of a solenoid that slaps back-and-forth, or a solid-state unit, it's a no brainer. It's no surprise that according to the APRA, the starter solenoid has the highest failure rate of any vehicle component. If you are in the solenoid business, this is great news. If you're a consumer and you want a component to last forever, a solenoid is not your answer.

A solenoid used for "isolation" is no different. A voltage sensing circuit simply provides an element of autonomy. My feeling....everything is a compromise. Go solenoid, it's cheap, easy to install, limited lifespan with ever-degrading performance. Silicon or Shottky solid-state isolators, tremendous voltage drop, get hotter than blazes, tough to find real estate to install, cost more than solenoids. MOSFET based solid-state isolators, easy to install, performance makes solenoids and traditional isolators seem downright elementary and power wastful. They come in varying sizes, capacities, performance, and price; price being the biggest objection as a MOSFET isolator that handles 600 amps can run you $500. A solenoid will run $10, but at that current rating, it would be dead within ten on-off cycles.

There's always a trade-off.

 

[Rich]

Fact: Solenoids are moving parts that are guaranteed to fail.

The published specs for the Bluesea solenoid are:

10,000 cycles @ 2000 Amperes @ 28 Volts DC
100,000 cycles @ 200 Amperes @ 28 Volts DC

At the 12 volts and the much lower current for automotive charging I wouldn't be expecting failure within the lifespan of the vehicle it is installed in.

 

[mobi-arc]

If you read a manufacturer's specs and take them as gospel....got a bridge I'd like to sell you. Take everything you read with a grain of salt. When was the last time you bought a 2x4 which actually measured 2x4? Do your own testing, exercise common sense, and talk to smart people. Most people don't really understand what a tremendous amount of energy 2000 amps is. I think you'll find that if you run those specs past a design engineer who specializes in power managment, his response will be something like......bull****! In our business, we come across specs that are wrong all the time. Sometimes they're wrong by mistake, sometimes by design.

With respect to the products functionality, I don't doubt that it works. I don't believe for a second that it will switch 2000 amps 10,000 times, nor do I believe that it's capable of 1 million cycles which is another marketing spec I've seen thrown around by Tyco/Blue Sea. And, like any solenoid, it's guaranteed to fail and degrade in performance over time....that's what soldenoids do. The only way to counter continuous degradation is to break-before-make; turn off the load prior to connecting the source.

The published specs for the Bluesea solenoid are:

10,000 cycles @ 2000 Amperes @ 28 Volts DC
100,000 cycles @ 200 Amperes @ 28 Volts DC

At the 12 volts and the much lower current for automotive charging I wouldn't be expecting failure within the lifespan of the vehicle it is installed in.

 

[Rich]

Here's the spec sheet. http://relays.tycoelectronics.com/datasheets/ev200.pdf I expect that the specs were authored by a "design engineer that specializes in power management".

 

[bulldog-yota]

Well the starter on a vehicle uses a solenoid that actually passes a lot of current everytime it is used. That is not true for an isolation solenoid which rarely will see more than a few amps on most uses.

Also keep in mind that Mosfet devices also have a limited lifetime and degrade over their lifespan. Not in a similar way as a solenoid, but they still do degrade. One thing that kills mosfet life span is high current and especially high temps, which makes it a real issue when installed in the engine bay. Also keep in mind that a short circuit can easily destroy a mosfet, while it is less likely destroy the solenoid.

So making claims that one will work better than the other is really more dependant on how well each has been designed. Both degrade over time, the electronic device less so from the current, but much more so because of heat.

 

[mobi-arc]

Agreed to a certain extent, the caveot being that if the device is designed to run cool, you greatly expand the lifespan of any device. Unfortunately, the inherent design of a typical solenoid, switched while under load will generate tremendously more heat, by a factor of 100 or more than a MOSFET device appropriately designed to handle the same amount of current.

Well the starter on a vehicle uses a solenoid that actually passes a lot of current everytime it is used. That is not true for an isolation solenoid which rarely will see more than a few amps on most uses.

Also keep in mind that Mosfet devices also have a limited lifetime and degrade over their lifespan. Not in a similar way as a solenoid, but they still do degrade. One thing that kills mosfet life span is high current and especially high temps, which makes it a real issue when installed in the engine bay. Also keep in mind that a short circuit can easily destroy a mosfet, while it is less likely destroy the solenoid.

So making claims that one will work better than the other is really more dependant on how well each has been designed. Both degrade over time, the electronic device less so from the current, but much more so because of heat.

 

[cruiseroutfit]

mobi-arc, I don't doubt the fact your product will last longer than a typical solenoid style... But who here has actually had a solenoid isolator fail? I know of Wrangler units that are 10-15 years old and still work as they did they day they were installed (mine has been working great for 5 years now). On top of that, if a solenoid fails, your looking at ~$50 for a replacement, cheap insurance you could carry in your spare parts if it mattered.

Sure I have had solenoids fail (such as on a starter), but it was usually on a 30 year old LC starter that hadn't seen use in many years, the contact were probably covered in rust & water...

 

[firetruck41]

For others reading this thread that didn't know, Mobi-arc sells the Powergate, an alternative dual batt manager, so he has a different perspective and motivation regarding these systems. FWIW, the powergate does look like a quality unit for more $$$. When I get dual batt system, it will probably come down to how much $$$ I can spend at the time, as even the solenoid systems seem to have a decent lifespan/reliability for many members on the board.

 

[waskillywabbit]

I run a "triple" battery system set up w/ the Painless Wiring dual battery kit w/ some modifications that works flawlessly.

I have (1) battery in the stock location and the other (2) in the rear cargo area. Everything is setup using the Painless Wiring diagram except where the battery cable goes to the 2nd battery in their diagram, mine goes to a Marine battery manual switch that separates the (2) rear dual batteries. This allows me to alternate between charging these (2) rear batteries and keeping everything separate. Each of the batteries can be read on an in-dash voltmeter so I know which one needs to be charged if any with a quick glance, the front one on the stock gauge and the rear two on Autometer voltmeters. Only inconvenience is the marine battery switch when I have to "switch" it, but that is really trivial.

 

[bulldog-yota]

mobi, I think you are greatly exagerating the contact wear on a solenoid used for isolater/combiner purposes on a vehicle. In most applications that solenoid sees far less duty than the starter solenoid. It normally only closes once after the engine is started and then only opens after the engine is shutdown. I use a Surepower unit sold by Wrangler, with some elctronic bits that open and close at certain voltage to auto charge and prevent main battery discharge. It is simple to install and you don't have to mess with the main system wiring.

Solenoids have their weaknesses that one day they will fail as they wear out, the thing is most of them will outlast the vehicle since they dont work very hard in most cases. The advantage though is that they are very robust devices, which easily can handle voltage spikes and current overloads. They are also far less affected by environmental tempratures.

I have spend plenty of years working with power MOSFETs and they are mostly used in circuits that require continues switching over the period of operation. Something a mechanical device is not up to task. However these devices are very finiky and probably the most prone to failure of any semiconductor, the price you pay to handle high power in electronics. One they can not handle a good current overload or voltage spike, just one sufficient spike will kill them. That is the reason why designers build in many protection circuits around them, but that is still not foolproof. Secondly the environment temprature plays a very large role in the MTBF of these devices, this and voltage/current spikes do actually degrade the performance of the MOSFET.

Now back to isolators. The fact is they do very little high current work and you normally connect the batteries together before you do winching i.e. high current work. Secondly the MOSFET device can not handle short circuit loads (2 high capacity batteries with one completely drained), even your own company ackonowledges it, while the solenoid tends to survive a number of those. Lastly the solenoid will handle its continues rated current easily at 70-80C. I have to see the powergate device handle its rated current of 300A at 70-80C continuesly, remember that small box has to dissapate 19W at an ambient temprature of 70-80C which can easily happen under the hood in summer time.

So I guess what I'm trying to say don't knock an old school technology till your modern technology is proven for many years for the application in discussion. The reason why I'm saying this is that I have worked long enough with power electronics and have seen enough failures due to reasons listed above, to know in short that I seriously doubt the MOSFET device will outlast a solenoid device in the hands of a normal user for this appllication. In fact I'm willing to bet under hard abusive circumstances the solenoid will outlast the MOSFET device.

Just my opinion and what was the topic again???

 

[bulldog-yota]

Hants, some reading that might help you.
http://www.surepower.com/pdf/separatorinterconnect.pdf
http://www.toyota120.com/GenDocs/dualbattsep.pdf

I have been happy with mine, works very easy and allows you to override. What I like most is that you don't have to mess with the main wiring of the vehicle, so if it fails for whatever reason your vehicle will work as normal and the second battery with acc hanging of it will just die.

I believe there are some other companies making similar devices, but the idea is pretty much the same. You hook it up and forget about it for the most part. Till you need to winch or need the 2nd batt to help with starting. TJM makes a fancy version with voltage readings, I believe it is the IBS and costs a premium. Surepower makes a less fancy version, which just uses the ignition or manual switch inputs to connect, I think they are a bit less expensive.

The Surepower unit can be bought at Wrangler (or other distributors but I don't have the link ready ).
http://www.wranglernw.com/commerce/ItemDetail.asp?ItemNo=17-MBS200


Oh BTW, ARB actually resells the Surepower unit in Oz and other places, so I doubt they would do it if it was junk.

 

[firetruck41]

I have seen the surepower units for sale online at RV parts/suppliers for around $80-90.