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Discussion Starter · #1 ·
I am looking to fit a dual bat system into my GU7 Patrol. From what I understand most dual bat isolators are only about 95% efficient. I take it that this means that the aux bat will only be charged to 95% of its full capacity.

So what are my options? Can you just wire in a 240V bat charger and use mains power to top up the aux?

Do you need to disconnect the aux bat from the dual bat system before using the 240V bat charger?

Also what would be the minimum charge rating that you would go for in a dual bat isolator? I have seen dual bat management systems rated at 140, 150 and 180A.

What would you guys recommend?

Thanks in advance,

Steve
 

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Dual battery systems

I am looking to fit a dual bat system into my GU7 Patrol. From what I understand most dual bat isolators are only about 95% efficient. I take it that this means that the aux bat will only be charged to 95% of its full capacity.

So what are my options? Can you just wire in a 240V bat charger and use mains power to top up the aux?

Do you need to disconnect the aux bat from the dual bat system before using the 240V bat charger?

Also what would be the minimum charge rating that you would go for in a dual bat isolator? I have seen dual bat management systems rated at 140, 150 and 180A.

What would you guys recommend?

Thanks in advance,

Steve
Hi Steve, welcome to Patrol 4x4

I'll put up some answers, and I'm sure our more learned electricians on here will come along and fill in the details. I have reasonable electrical experience myself, so should be of some help.

Battery Charging
You are really going to struggle to get a battery to 100% capacity, it doesnt happen, even after a really long charge, unless you've got a decent 7 stage battery charger. Your alternator is a fairly rudimentary battery charger. Also, the output of the alternator is in the region of 90A. You lose some of that just to run the vehicle ie fuel pumps, lights, ECU etc, so your charging current could be around 50A depending on conditions.

Mains charging.
Yes you can charge the auxillary battery from a battery charger, and you dont need to unwire or isolate the auxillary battery from the main battery. Obviously you'll need a 240V supply to charge. That may not be available everywhere.

Isolators.
I went with a 200A Red Centa Isolating relay, and it has done it's job well. Most of the isolators out there do a good job, If I did mine again (and I will end up doing this anyway) is to have an electronic relay (Maybe Projecta 150A) as the main relay, but back it up with a manual isolator. Could save you if you need to jump start off the auxillary for any reason.

Reccomendations?
Do you have good memory, and are unlikely to forget anything..........manual isolator. If you have poorer memory, or want to let things take care of themselves, then go with an electronic isolator with approx 150A load. If you want redundancy, go both.

Hope this helps.
 

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Hi 5.11, could you elaborate a bit more on this 95% efficiency of a dual battery isolator, because I have never heard of such a thing.

All standard ( solenoid/relay ) type isolators have no effect on the efficiency of the way auxiliary batteries are charged, this is entirely controlled by the vehicle’s alternator and is one of the primary advantages of using solenoid/relay type isolators.

Next, the maximum charging rates you are likely to ever come across in the average dual battery system is no more than about 70 amp and there are many factors to why this is the case, like the maximum available current coming from your alternator, the location of your auxiliary battery(s), the size and length of cables connecting all the batteries to together and so on.

Unless you are using an isolator for joining two batteries together for winching, anything over 80 amps is more for show than any real advantage.

Even when an isolator has emergency jump start, most relays and solenoids will tolerate high current bursts without any damage being caused. It is only when high currents need to be carried for long periods of time, like when winching, that the relay or solenoid needs to have a high CONSTANT current rate.

This is one of the problems with the way many solenoid/relay type isolators are marketed.

Many will advertise one current rate, but you need to know exactly which current rate they are advertising, the CONSTANT current rate or the MAKE current rate ( the high current burst rate ).

Unless both rates are clearly displayed, I would be very cautious about just how much current the particular isolator can actually tolerate in a dual battery system.

There is a lot more to this subject but this is a start.
 

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capiblke of 100% charge of AGM, GEL, Calcium and led acid batteries
Hi mikegq, they are all lead acid batteries and with the exception of Calcium/Calcium, the average alternator can also charge lead acid batteries to 100%, so whats your reason for spending a fortune to achieve something that your alternator can already do?
 

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AGM. GEL AND CALCIUM will NOT charge 100% from alternator charge. 95% yes but the last 5% requires specific charge cycling and spiking to fully saturate that is what 5.11 is refering to.
infact most manufactures state 80% as a figure of maximum charge of those batteries from the vehicles alt. sorry buddy

A standard Lead acid Flooded vented battery doesnt apply here
 

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The nutty professor
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all i can say is

ford starter relay or any other heavy duty relay rated at around 100 amps, wired to energize when the ignition is turned on, a 30 amp circut breaker if your 2nd battery is an agm , and wiring to join and earth the batteries, and some 100 amp fuses if you are worried

simple and cheap, charges with the motor running, isolates the batteries when you turn the car off

that 5% would last 30 mins if you are lucky, depending on what you are running, just use a home charger before you leave to top it right up if you are really worried about it
 

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AGM. GEL AND CALCIUM will NOT charge 100% from alternator charge. 95% yes but the last 5% requires specific charge cycling and spiking to fully saturate that is what 5.11 is refering to.
infact most manufactures state 80% as a figure of maximum charge of those batteries from the vehicles alt. sorry buddy
Hi again milegq, and can you show one single battery, alternator or vehicle manufacture that makes anything like a statement like that. There is no such thing.

And there is no reason why a standard alternator can not FULLY charge AGM and Gel batteries to 100%, especially when both of these types of batteries are easier to charge than your standard cranking battery.

I don’t know where you got that incorrect info from but I’ll take a guess and say it was form one of the DC-DC converter sellers advertising hype, the problem is that it’s just that, advertising hype.

Oh and BTW, a Calcium/Calcium battery can be charged upwards of 95 to 97% by a standard vehicle alternator and this info comes from one of Exide's web sites.
 

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all i can say is

ford starter relay or any other heavy duty relay rated at around 100 amps, wired to energize when the ignition is turned on, a 30 amp circut breaker if your 2nd battery is an agm , and wiring to join and earth the batteries, and some 100 amp fuses if you are worried

simple and cheap, charges with the motor running, isolates the batteries when you turn the car off

that 5% would last 30 mins if you are lucky, depending on what you are running, just use a home charger before you leave to top it right up if you are really worried about it
I am with you, this set up is cheap and works really well.

If you are concerned that it might not be fully charged just put it on a home charger periodically.

I have this setup on my current vehicle and it works well.
 

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Hi 5.11, could you elaborate a bit more on this 95% efficiency of a dual battery isolator, because I have never heard of such a thing.
He didn't say a dbs, he stated about the alternators capabilities to charge batteries to a true 100% capacity in car as obviously they are always in use in some way.
He didn't mean any DBS could not do it (as they are just a gadget for passing power to batteries with the power available to it), but an alternator could charge a battery to near 100% if there was more power available to it than what was being used, one reason why alternators have regulators to prevent overcharging.
Also most batterys begin their deterioration from the moment it's made so it's ability to take or hold a true 100% full charge as it ages is very unlikely.
 

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He didn't say a dbs, he stated about the alternators capabilities to charge batteries to a true 100% capacity in car as obviously they are always in use in some way.
No, mikegq had already stated ( wrongly ) that manufacturers state 80% maximum charge.

So is he talking about the isolator, the alternator or the battery as being the reason for not being able to fully charge a battery?

As requested, could mikegq please be more specific.
 

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Im not on this forum to argue, just to help people out who genuinely want it. Everyone will have a differant opinion here so its a waste of time. 5.11 asked a question and I simply answered. Ive always said " a little bit of knowledge is very dangerious" and its true. Thats not my fault and im not going to argue with them. Manufactures like "redarc" who have a fabulous name in the industry dont spend all there money designing products that have no use. Thats all I have to say on the matter.
If anyone one needs help with anything electrical them msg me, if u want to argue then dont bother i dont have the time :)
 

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Discussion Starter · #15 ·
Hi Graham99,

Thanks for the info. Backs up what I was thinking. As I only drive short distances to and from work I will have to use a 240V charger to maintain the aux bat. I will have to make sure the isolator be it solenoid or electronic can handle a 240V charger while it is still in the circuit.

Hi Drivesafe,
I had a look at some of the major dual bat isolator manufacturer’s web sites and listed on their product specifications page some of them list the efficiency of their devices. They range from about 80 to 95%.

If I go and spend big dollars on a good quality aux bat I will have to keep it maintained with a good quality 240V charger.

Thanks everyone for your advice.
Rgds,

Steve
 

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The nutty professor
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Hi Graham99,

Thanks for the info. Backs up what I was thinking. As I only drive short distances to and from work I will have to use a 240V charger to maintain the aux bat. I will have to make sure the isolator be it solenoid or electronic can handle a 240V charger while it is still in the circuit.

Hi Drivesafe,
I had a look at some of the major dual bat isolator manufacturer’s web sites and listed on their product specifications page some of them list the efficiency of their devices. They range from about 80 to 95%.

If I go and spend big dollars on a good quality aux bat I will have to keep it maintained with a good quality 240V charger.

Thanks everyone for your advice.
Rgds,

Steve
i wouldnt stress too much about the "maitanance" of the aux battery unless you are using it everyday with the motor off, if it is only being used when out camping then the daily drive to and from work should be enough to fully charge it, even with a basic isolator set up, when you are out camping on the other hand and the 2nd battery is being used alot then short trips will struggle to fully charge the 2nd battery ,but enough power will be put back in to get you by as long as the drive isnt too short

it normally takes a couple of hours of driving to fully charge the batteries , so unless you dont want to drive around every now and then when camping then i suggest a solar set up to suplement the battery
 

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Hi 5.11, can you post a link the this info, I’m not sure you are reading correctly.

If it’s a purely electronic type switching isolator then this may be the case.

But as the vast majority of isolator use relays/solenoids to do their switching and as such, these devises have no effect on the charging capability of a battery to the point where they will actually restrict the battery’s charge capacity.

As posted earlier in this thread, when relay/solenoid type isolators are used, the primary charge control is done by the vehicle’s alternator. So the 80 to 95% is a mystery.

Also 5.11, ITS A FORD NOT A NISSAN’s post is right on the money.

Mikegq, the basic idea of all forum of this nature is to help, but, as in your case, why post up something, then when questioned about it’s validity, you choose to declare foul play rather than, as requested, follow through with some legitimate support info.

If you have valid credible info to back your claim, then posting it up for all to see will negate any arguments, running off to send MPs is just proving the obvious, but that your choice.
 

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Anyone using the ABR/Sidewinder gear?
 

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Ahhh well, that fizzed out pretty quick. :D

5.11 ...
I have a series 6 not a 7 but there is no difference to the Electrical Supply or Charging System I am aware of that will affect your systems differently to mine and I have a Redarc Solenoid fitted between Cranker and the Aux's and run up to 4 N70's in various configurations on extended trips. Our work vehicles include Series 7 Patrol 4.8, Cruisers and Landies also have Redarc systems and we have yet to see a serviceable Aux battery capacity down to 80 or 90% compared to the Cranker

Redarc style 'smart' solenoids and 'dumb' solenoids such as a Starter Solenoid will not affect the charging capacity from the vehicle into the Aux battery and can be considered 100% efficient in that specific aspect to all intents and purposes. Feel free to fit one with absolute confidence that whatever SOC you will get into your Cranker you will get into your Aux given sufficient engine running time IE you won't get 40 Amp Hours capacity in 1 hours running time back into an Aux or a Cranker using the Alternator or a Ctek.

I have NEVER had to use a 240 Volt charger to top up any of my Aux batteries that were given sufficient Alternator run time and when hooked up to a Ctek style charger after extended trips the Charger almost immediately shows the Battery as fully charged and goes into "float" waiting for the next trip.

Obviously any of the Batteries that might have been taken out of circuit DO require a recharge from the Ctek and I don't deny however that the Ctek per se will assist in desulphating etc that the Alternator/Regulator system is not capable.

Solenoid Rating - 100 Amp continuous is more than enough unless you have a high current application such as Winching or large Inverters or whatever. The 150 amp Projecta or 200 amp continuous rated Redarc is then probably a better choice

DC/DC converters - Don't get confused with the advertising hype around DC/DC converters if you come across them. They have there place in low voltage DC electrical/electronic applications (and a very practical one at that) BUT not in a correctly spec'd and installed Dual Battery System as there are inefficincies in the conversion process.



Anyway, like all posts on the Forum thats my opinion. Consider or discard as you wish :cool:
 

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Further to the DC/DC converter as I can't amend the post due to Server Error message.

Readarc for example in the BCDC specifications state the Product is used "where the distance from the main battery may cause a significant voltage drop" as these devices are aimed at using Vehicle supply to charge Aux batteries in Caravans and Boats etc.
 
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