which? two 6 volt or one 12volt battery?
- Thread starter Bbasso
- Start date
Bbasso
Expedition goofball
I don't think I can separate the alternators for independent duty... I could be wrong but these 7.3 take a lot of starting power. I know the batteries handle the starting but dual alternators charge them up way quicker.
Hopefully sooner than later I aim to put a 100wt panel on the roof with a charge controller inside to keep the house battery (s) topped off and in good shape.
And that brings me back to my original question.
Would I be better off with a single BIG 12v battery or two 6v for house duty only?
Which is the smarter choice?
(Size and weight are not an issue but cost is)
Again thank you for all the help.
Hopefully sooner than later I aim to put a 100wt panel on the roof with a charge controller inside to keep the house battery (s) topped off and in good shape.
And that brings me back to my original question.
Would I be better off with a single BIG 12v battery or two 6v for house duty only?
Which is the smarter choice?
(Size and weight are not an issue but cost is)
Again thank you for all the help.
jbob
Observer
I need to look at the 7.3 I just bought -- now I'm curious as to whether it has dual alternators as well. I do know it started just fine with a new battery under the hood and the second one disconnected at temps below freezing. Not that you'd want to run it that way, but it's a data point.
Each cell is nominally 2V, so a 12V battery has six cells, and each 6V battery has three. So there's really no difference between a really big 12V and two 6V, except the 6V batteries enable you to move and mount each set of three cells independently. Have you priced out the two options? While the Trojan T-105 seems to be the "gold standard", I believe a lot of Costcos sell 6V GC batteries (~ $85/each), and my local Batteries Plus has them for < $100/each.
olsen_karl
Adventurer
For my truck camper, I decided to go with the two 6V golf cart batteries from Costco. I had the space, and this is the least expensive way to get that many amp-hours. Also, according to what I've read while researching deep cycle batteries, GC batteries are supposedly ruggedly built and can handle repeated deep discharges -- more than the combination "marine/starting" deep cycle 12V batteries that I found while searching. True deep cycle 12V batteries (i.e. no CCA rating, not sold as a trolling or combination starting battery) are quite expensive.
FWIW, I vented my two GC battery setup by putting them in an action packer type plastic box (Walmart), and attaching the factory flexible hose vent to the lid of the plastic box, using some Home Depot PVC fittings. The two GC batteries fit well inside this box -- a little room for wiggling them in place, but they can't shift sideways more than a few mm.
FWIW, I vented my two GC battery setup by putting them in an action packer type plastic box (Walmart), and attaching the factory flexible hose vent to the lid of the plastic box, using some Home Depot PVC fittings. The two GC batteries fit well inside this box -- a little room for wiggling them in place, but they can't shift sideways more than a few mm.
4x4junkie
Explorer
I don't think it would make much of a difference, if any (only if the starting batteries were deeply discharged would it take longer to recover them with a single alt).
Starting the engine takes a small amount of energy from the batteries (relatively speaking), meaning the batteries will remain close to fully-charged. A battery that is near full-charge is slow to retake that small amount of energy (taking several minutes or longer) at a current usually less than 10 amps , which should be well within the capability of a single alt.
So ×2, I would also say get rid of that diode box and separate the two alts if you can.
And FWIW, I'm not quite sold on costly AGM batteries yet myself. I've got a pair of Delco Voyager flooded deep-cycle units that are over 9 years old (and another pair over 5 years old) that are all still going strong. That said, unless you can come up with a decent ventilation system (or relocate it under the floor maybe), I would say an AGM unit is the better choice to have inside the back there. If you can vent it though, go with the GC batts.
wrcsixeight
Adventurer
A problem with alternator charging an Auxiliary battery is the fully charged engine battery(s)
Tacked onto the charging circuit, the voltage regulator does not really "see" the extra battery. Since it is distant and the fully charged starting batteries voltage rises easily, the voltage regulator decides that the alternator does not need to make much juice.
Having one alternator hooked directly to the Auxiliary battery will allow the depleted battery to suck as many amps from the alternator as it wants at the voltages allowed by the VR.
With 2 alternators, there is no need for that voltage dropping isolator. An alternator dedicated to an Auxiliary battery will charge them much better than 2 alternators that see the engine batteries first, and with that isolater, not at all. Mere scraps of current will make it to the Aux battery
Deplete it, and put a clamp on DC ammeter over one cable leading to the battery terminal. I bet you'll see no more than 10 to 12 amps. An alternator directly feeding this same depleted battery will initially provide 50+ amps, and the batteries life and performance during that lifespan will be many times than anything that makes it through that isolator.
Tacked onto the charging circuit, the voltage regulator does not really "see" the extra battery. Since it is distant and the fully charged starting batteries voltage rises easily, the voltage regulator decides that the alternator does not need to make much juice.
Having one alternator hooked directly to the Auxiliary battery will allow the depleted battery to suck as many amps from the alternator as it wants at the voltages allowed by the VR.
With 2 alternators, there is no need for that voltage dropping isolator. An alternator dedicated to an Auxiliary battery will charge them much better than 2 alternators that see the engine batteries first, and with that isolater, not at all. Mere scraps of current will make it to the Aux battery
Deplete it, and put a clamp on DC ammeter over one cable leading to the battery terminal. I bet you'll see no more than 10 to 12 amps. An alternator directly feeding this same depleted battery will initially provide 50+ amps, and the batteries life and performance during that lifespan will be many times than anything that makes it through that isolator.
Bbasso
Expedition goofball
I could possibly move the batteries underneath the van but the costs getting two stock battery boxes would be too costly for me at the moment. later down the road I would like to but only a group 31 battery would fit. So house batteries will be inside the van from day one.
Unless there is a huge influx of money suddenly that will allow me to build a custom stainless steel battery box to mount underneath. Lol
As for only needing one battery to start a 7.3, I won't take the chance. Especially when the temps drop into the single digits when the glow plugs need all the time to heat up.
As for splitting up the alternators, I'd honestly rather not. If it means adding some more expenses then so be it.
Unless there is a huge influx of money suddenly that will allow me to build a custom stainless steel battery box to mount underneath. Lol
As for only needing one battery to start a 7.3, I won't take the chance. Especially when the temps drop into the single digits when the glow plugs need all the time to heat up.
As for splitting up the alternators, I'd honestly rather not. If it means adding some more expenses then so be it.
wrcsixeight
Adventurer
Well look at it like this, that surepower isolator is a power robber. If you want a smart simple and better device in the same place you are looking at another 50 to 100$. If alternator charging is to be the primary recharge method, then getting rid of the surepower will save you money in batteries down the road, because chronic undercharging is batterycide.
If you reroute the one alternator cable to go only to the single house battery, you do not need an isolator. Expense saved. Much better chance batteries get closer to full charge every time you drive
You probably do not even need a new cabling as the previous owner likely just pulled power from one of the engine batteries.
Hopefully they are already fused and all you have to do is move the cable from one engine battery to alternator. (+) stud
I would not, and did not recommend removing a battery from diesel starting duties.
A little more complexity if the voltage regulator is not inside the alternator itself.
Don't personally know Fords so won't elaborate on that
If you reroute the one alternator cable to go only to the single house battery, you do not need an isolator. Expense saved. Much better chance batteries get closer to full charge every time you drive
You probably do not even need a new cabling as the previous owner likely just pulled power from one of the engine batteries.
Hopefully they are already fused and all you have to do is move the cable from one engine battery to alternator. (+) stud
I would not, and did not recommend removing a battery from diesel starting duties.
A little more complexity if the voltage regulator is not inside the alternator itself.
Don't personally know Fords so won't elaborate on that
Weasel with a Diesel
Observer
Well, I read now a couple of times the Diode isolator causes a voltage drop.
So far so good.That's correct.
Did anyone of you has used a diode isolator in the past?
Gents: It is a Sure Power isolator with an extra "E" regulator input!
Are you blind?
This compensates the voltage drop just by increasing the alternator output voltage about the same amount of the diode voltage drop simply by routing one contact of the regulator brush directly into the diode E reg input....
I'm using Sure Power since a couple of years (by the way, they are in business since 1959) and never had any problems with undercharged batteries.
That is a myth created by folks not knowing either how to use them or how they work.
Diode isolators simply do their job.
If you want trouble - then go with solenoids. I wouldn't look back into that direction.
Sure power even sells a diode coupler to charge a single battery with two alternators.
Does this looks like a voltage drop?
It's a Battery monitor measuring the charge current (10.0A) and voltage (14.2V) directly in front of the supply battery poles (about 15 feet behind the battery diode isolator!):
And you can see that the battery (Optima yellow top) is about 80% charged, still being charged with a current of 10 A.
So far so good.That's correct.
Did anyone of you has used a diode isolator in the past?
Gents: It is a Sure Power isolator with an extra "E" regulator input!
Are you blind?
This compensates the voltage drop just by increasing the alternator output voltage about the same amount of the diode voltage drop simply by routing one contact of the regulator brush directly into the diode E reg input....
I'm using Sure Power since a couple of years (by the way, they are in business since 1959) and never had any problems with undercharged batteries.
That is a myth created by folks not knowing either how to use them or how they work.
Diode isolators simply do their job.
If you want trouble - then go with solenoids. I wouldn't look back into that direction.
Sure power even sells a diode coupler to charge a single battery with two alternators.
Does this looks like a voltage drop?
It's a Battery monitor measuring the charge current (10.0A) and voltage (14.2V) directly in front of the supply battery poles (about 15 feet behind the battery diode isolator!):
And you can see that the battery (Optima yellow top) is about 80% charged, still being charged with a current of 10 A.
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4RunAmok
Explorer
I'm well aware of Sure Power and their products.
The problem is that others that don't know the difference between a Sure Power with an E post, and a standard diode isolator without the compensation, and may just assume one is just like the other, and go with the cheaper part to save a couple bucks.
I typically do not recommend any old solenoid. I advocate using the Blue Sea 7622 Automatic Charging Relay, rated at 500 Amps Continuous Duty, and over a 1000 amps peak. Tested thoroughly on the high seas and proven durable. The magnetic latching mechanism uses milliamps to operate, so you can leave batteries combined with no active charging source and it won't cause a draw on the system like a regular relay would.
I'm glad you've got your sure power system and that it works for you, but I can use a 7622 without having to tap my alternator, using less wire for the same result.
The problem is that others that don't know the difference between a Sure Power with an E post, and a standard diode isolator without the compensation, and may just assume one is just like the other, and go with the cheaper part to save a couple bucks.
I typically do not recommend any old solenoid. I advocate using the Blue Sea 7622 Automatic Charging Relay, rated at 500 Amps Continuous Duty, and over a 1000 amps peak. Tested thoroughly on the high seas and proven durable. The magnetic latching mechanism uses milliamps to operate, so you can leave batteries combined with no active charging source and it won't cause a draw on the system like a regular relay would.
I'm glad you've got your sure power system and that it works for you, but I can use a 7622 without having to tap my alternator, using less wire for the same result.
Weasel with a Diesel
Observer
Thank you for your Comment 4RunAmok.
I don't want to sound offensive- I'm just getting tired of the amount of misinformation floating around.
I do use a diode isolator without an E post since I have an external regulated Nippon Denso alternator.
I would never use an relay again.
I still remember how often we have been left stranded in our VW camper with dual batteries. The supply battery was drained and robbed power from the starter battery as soon as the relay was closed. Leaving us stranded with two drained batteries.
This can thankfully not happen with a diode isolator.
I don't want to sound offensive- I'm just getting tired of the amount of misinformation floating around.
I do use a diode isolator without an E post since I have an external regulated Nippon Denso alternator.
I would never use an relay again.
I still remember how often we have been left stranded in our VW camper with dual batteries. The supply battery was drained and robbed power from the starter battery as soon as the relay was closed. Leaving us stranded with two drained batteries.
This can thankfully not happen with a diode isolator.
4RunAmok
Explorer
We can argue for Ford/Chevy, PC/Mac, Snap-On/Matco, all day long everyday forever.
I build systems for "mission critical" uses, such as Emergency and Law Enforcement vehicles, as my profession. It's important to know what works and what does not, and how to build a system that operates correctly and reliably. Standards in this industry exist for a reason. There's always an optimal way to do things. Are any of them fool-proof? Nope. ALL SYSTEMS FAIL, eventually.
Everyone should only modify something to the extent they're comfortable with, or have prepared for the consequences by having extra parts, or using a part that operates automatically and manually (like the Blue Sea 7622
)
I build systems for "mission critical" uses, such as Emergency and Law Enforcement vehicles, as my profession. It's important to know what works and what does not, and how to build a system that operates correctly and reliably. Standards in this industry exist for a reason. There's always an optimal way to do things. Are any of them fool-proof? Nope. ALL SYSTEMS FAIL, eventually.
Everyone should only modify something to the extent they're comfortable with, or have prepared for the consequences by having extra parts, or using a part that operates automatically and manually (like the Blue Sea 7622
)
Weasel with a Diesel
Observer
Interesting, I'm close to that industry too.
But law enforcment/emergency, military over here uses Lithium-ion-systems:
-2/3 less weight
-1/3 the space consumed of conventional systems
-10 years life expectancy with a full cycle per day
-recharged within 1 hour
That standard, you use is lets say a bit outdated?
But law enforcment/emergency, military over here uses Lithium-ion-systems:
-2/3 less weight
-1/3 the space consumed of conventional systems
-10 years life expectancy with a full cycle per day
-recharged within 1 hour
That standard, you use is lets say a bit outdated?
DiploStrat
Expedition Leader
Don't do this for a living, but I have spent the better part of a year studying these issues and and fair amount of money testing various products. There are a couple of ways to accomplish what you want and while none of this is hard, it is a bit complex. I wrote a small paper on the "problem" which I will happily share if you send me an e-mail.
If you only want to charge a small camper/house (as opposed to a truck/starter) battery, placed under the hood or close to your alternator(s) and starter battery, then all is very easy. If you want to charge a large (400+Ah) camper battery placed far (10+ feet) from the engine compartment, then things get harder.
If you only want to charge from the engine alternator, then things are easy. If you want to share the charge from engine, solar, and shore power, then things get more complex, but, in some ways, easier.
When working with a "12 volt" system, voltage drop is the enemy. In order for a 12v battery to charge "fully" (call it 12.6v - 13v) you are going to have to give it a charging voltage of between 14.2 and 15.2v, depending on the type of battery and the temperature at the battery. Most AGM batteries sold in the U.S. want about 14.2v at 70F. Open FLA batteries want up to 15v under the same circumstances. Even AGM batteries want about 15.1v at 20F. If the voltage difference between the charge source and the battery is too low, then the charge rate will be very low. That is, it will take a very long time.
Once you have enough voltage, then you need enough current. AGM batteries need a minimum of 25A charge for every 100Ah of bank size. They would like C/1, that is 100A for every 100Ah and can accept up to C/5, but no one has a charger that large. So basically, you want 100A for every 100Ah of camper battery. (Good luck finding that.) And, it gets worse; for every 100Ah you discharge, you need to recharge between 110Ah and 1250Ah.
Finally, you need time. Battery charging is a chemical reaction and modern chargers lower the charging rate once the battery passes about 80% charged. (Call it 12.4v.) You can guesstimate that the battery will require about two hours of "absorption" charging after it reached "full" charge. Shore or solar power are about the only practical ways to achieve this.
All of this argues that on an overland vehicle, you want to be able to harvest as much current as possible from your truck alternators while driving (this is called "Bulk" charge) but you have to recognize that with any battery bank over 100Ah, you may never drive long enough to achieve a full charge. This argues for a solar kit or shore power to complete you charge. This is very important as lead acid batteries loose their ability to accept a charge over time if they are not fully recharged regularly, say, at least once a week. (Equalization/desulphation cycles may be able to help this, but regularly recharging fully is best.)
Sooo, what to do?
If your alternator does not put out at least 14v, then you need a way to boost your charging voltage. In this case you might look at:
-- An A2B such as those made by Sterling Power: http://sterling-power-usa.com/12volt-210ampalternator-to-batterycharger.aspx Available in 200A and 400A models, these work as claimed. (I installed one.) They may not work on a modern truck as the 200A model, at least will shut down if it is fed 15.5v as it will be during the winter. Part of the "magic" of this device is its ability to run a sense wire to the camper battery and thus compensate for voltage drops in your wiring harness.
-- A B2B, such as those made by Sterling or CTEK (and others) will work, but can typically supply only about 50A. They CAN be paralleled and, because the 50A is provided at a full 14+ volts, can work well in an older truck with a 13 volt system. Here again, you mount this beast close to the camper battery in order to compensate for losses.
Both of these are diode based systems that put a voltage amplifier after the diode to compensate for the loss. Because they are diode based, they do not allow charging of the starter battery from the camper battery.
-- There are various ways you can scam your alternator into producing a higher voltage. The easiest is to add some form of controller, like one of these from Mechman: http://store.mechmanhighoutputalternators.com/voltage-control-modules/ This can be very useful as long as you measure your voltage at the load, not at the alternator output terminal. (And, of course, as long as all loads see only the reduced, not the boosted voltage.) A problem may arise with loads that are close to the alternator and which would see the boost and loads that are distant and would not.
A diode isolator will induce a voltage drop of between .5v and 1.5v depending on the current passing through. There are a couple of issues with diode based systems:
-- You must compensate for the voltage drop, either through your efforts or by using a diode system that includes voltage compensation. (The Sure Power unit referenced above, appears to be able to do this in most applications.)
-- You must dissipate the energy lost as heat. That is why the diode has such massive heat sinks and fans. The need to compensate for this loss pushes up the cost and size of diodes that can handle 200A or more.
-- The diode passes current only one way, thus you cannot share any charge coming from the camper battery with the starter battery without additional circuitry.
Does this mean that diodes are bad? No, but it does means that you need to understand a bit about how they work.
If you only want to charge a small camper/house (as opposed to a truck/starter) battery, placed under the hood or close to your alternator(s) and starter battery, then all is very easy. If you want to charge a large (400+Ah) camper battery placed far (10+ feet) from the engine compartment, then things get harder.
If you only want to charge from the engine alternator, then things are easy. If you want to share the charge from engine, solar, and shore power, then things get more complex, but, in some ways, easier.
When working with a "12 volt" system, voltage drop is the enemy. In order for a 12v battery to charge "fully" (call it 12.6v - 13v) you are going to have to give it a charging voltage of between 14.2 and 15.2v, depending on the type of battery and the temperature at the battery. Most AGM batteries sold in the U.S. want about 14.2v at 70F. Open FLA batteries want up to 15v under the same circumstances. Even AGM batteries want about 15.1v at 20F. If the voltage difference between the charge source and the battery is too low, then the charge rate will be very low. That is, it will take a very long time.
Once you have enough voltage, then you need enough current. AGM batteries need a minimum of 25A charge for every 100Ah of bank size. They would like C/1, that is 100A for every 100Ah and can accept up to C/5, but no one has a charger that large. So basically, you want 100A for every 100Ah of camper battery. (Good luck finding that.) And, it gets worse; for every 100Ah you discharge, you need to recharge between 110Ah and 1250Ah.
Finally, you need time. Battery charging is a chemical reaction and modern chargers lower the charging rate once the battery passes about 80% charged. (Call it 12.4v.) You can guesstimate that the battery will require about two hours of "absorption" charging after it reached "full" charge. Shore or solar power are about the only practical ways to achieve this.
All of this argues that on an overland vehicle, you want to be able to harvest as much current as possible from your truck alternators while driving (this is called "Bulk" charge) but you have to recognize that with any battery bank over 100Ah, you may never drive long enough to achieve a full charge. This argues for a solar kit or shore power to complete you charge. This is very important as lead acid batteries loose their ability to accept a charge over time if they are not fully recharged regularly, say, at least once a week. (Equalization/desulphation cycles may be able to help this, but regularly recharging fully is best.)
Sooo, what to do?
If your alternator does not put out at least 14v, then you need a way to boost your charging voltage. In this case you might look at:
-- An A2B such as those made by Sterling Power: http://sterling-power-usa.com/12volt-210ampalternator-to-batterycharger.aspx Available in 200A and 400A models, these work as claimed. (I installed one.) They may not work on a modern truck as the 200A model, at least will shut down if it is fed 15.5v as it will be during the winter. Part of the "magic" of this device is its ability to run a sense wire to the camper battery and thus compensate for voltage drops in your wiring harness.
-- A B2B, such as those made by Sterling or CTEK (and others) will work, but can typically supply only about 50A. They CAN be paralleled and, because the 50A is provided at a full 14+ volts, can work well in an older truck with a 13 volt system. Here again, you mount this beast close to the camper battery in order to compensate for losses.
Both of these are diode based systems that put a voltage amplifier after the diode to compensate for the loss. Because they are diode based, they do not allow charging of the starter battery from the camper battery.
-- There are various ways you can scam your alternator into producing a higher voltage. The easiest is to add some form of controller, like one of these from Mechman: http://store.mechmanhighoutputalternators.com/voltage-control-modules/ This can be very useful as long as you measure your voltage at the load, not at the alternator output terminal. (And, of course, as long as all loads see only the reduced, not the boosted voltage.) A problem may arise with loads that are close to the alternator and which would see the boost and loads that are distant and would not.
A diode isolator will induce a voltage drop of between .5v and 1.5v depending on the current passing through. There are a couple of issues with diode based systems:
-- You must compensate for the voltage drop, either through your efforts or by using a diode system that includes voltage compensation. (The Sure Power unit referenced above, appears to be able to do this in most applications.)
-- You must dissipate the energy lost as heat. That is why the diode has such massive heat sinks and fans. The need to compensate for this loss pushes up the cost and size of diodes that can handle 200A or more.
-- The diode passes current only one way, thus you cannot share any charge coming from the camper battery with the starter battery without additional circuitry.
Does this mean that diodes are bad? No, but it does means that you need to understand a bit about how they work.
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