Redarc SBI12 & AGM?

Submitted: Saturday, May 01, 2021 at 09:14
ThreadID: 141663 Views:7798 Replies:5 FollowUps:7
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Just after a 2nd or 3rd opinion, I've read over the Redarc docs, but didn't notice anything.

Can you use the Redarc SBI12 to charge AGM batteries??

I suspect not, but I just want to make sure.

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Reply By: Member - pedro1 - Saturday, May 01, 2021 at 09:42

Saturday, May 01, 2021 at 09:42
SBI 12 is not a charger, all it is is a solenoid that cuts in a set voltage to allow the second battery to be charged. The cranking battery is therefore charged fully before the secondary starts to be charged.
The charge is from your alternator. If your fridge is connected off the secondary battery therefore won't flatten your cranking battery as it is isolated by the SBI 12
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Reply By: Frank P (NSW) - Saturday, May 01, 2021 at 09:45

Saturday, May 01, 2021 at 09:45
The SBI12 is an isolator, designed to separate the start battery and the aux battery to protect the start battery from external loads when the engine is not running. It doesn't charge batteries, it allows the alternator to charge them when the primary electrical system is ready to do so.

Whether or not that will work depends on a number of things, such as
- Alternator output voltage. Increasingly they are too low to fully charge an auxiliary AGM battery.
- Depending on the AGM battery you have chosen, it may (probably will ) have max charge current restrictions below what the alternator will deliver when the battery is at a low SOC. Exceed those and you risk reducing battery life.
- Cabling to the second battery.

You might be lucky. If you get the right combination of alternator output, battery charge requirements, get the cable sizing right it might work.

To assess a particular case like yours, more info is needed.


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Reply By: Member - Siringo - Saturday, May 01, 2021 at 09:56

Saturday, May 01, 2021 at 09:56
Thanks for the replies folks. I haven't purchased a battery yet, still looking.

I have 2 SBI12's . I'm trying to save a few $$$s so I may just go with an old style wet, deep cycle battery, the SBI12 should be fine to recharge that.

I need as a minimum 100Ah. It's going to run a single fridge that draws at worst case 2Ah and a few LED lights. The battery needs to mount under bonnet and can't be longer than 310mm.

If I have to I could buy a cheapish DC DC charger, spotted this this morning, wondering if anyone has any experience with these, DC DC Charger from ABR:

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Follow Up By: RMD - Saturday, May 01, 2021 at 10:35

Saturday, May 01, 2021 at 10:35
It is UNWISE to fit an AGM battery under the bonnet of anything as the heat of the engine bay will cut it's life short UNLESS you can definitely heat insulate it and feed it lots of cool air from the front of the vehicle so radiant heat doesn't kill it.
Unfortunately using the AGM so close to it's charging source means there will be not much cable voltage drop to limit current flow and so that will mean a high rate of charge on a low SOC battery as mentioned above. You haven't mentioned the vehicle charging system SMART or normal as that will have a bearing on IF you need a DCDC unit.

The quality of the AGM is another factor, and I charged mine in the tub of ute, directly from a cable via a solenoid, yes, when discharged , the current would be higher with a 100AMP alternator but the cable resistance over that distance limited the flow. Batteries, even when low SOC quickly see their voltage rise and that limits the flow of heavy current and the cable resistance also causes the, small alt to battery voltage differential, so all worked for me. The Full River AGM lasted 11 years charged like that. It seems no one ever really measures the actual flow into a LOW SOC aux battery from an alternator and most fear the alt output, ie, 100amps, to be terrible. You will never/rarely get the alternator to output it's maximum and when it's regulator sees a hold back. ie, Voltage rise from where it is delivering to, it reduces the alternator output accordingly. If cabling and length are suitable, then the system simply charges the battery, Best to check the dynamics if it all and how it works before spending more and more on unnecessary gear which will work but may not be really required.
A multi meter, ie, which includes a digital clamp meter. to read volts AND a feature of having the current clamp on that meter is to read charge cable current, will allow assessment of what really IS happening. The meter may save the cost of some fancy unnecessary but functional gear. You will never regret buying the test meter.
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Follow Up By: nick g1 - Saturday, May 01, 2021 at 10:47

Saturday, May 01, 2021 at 10:47
That will work but if you go with that understand that because of the charging profile ( constant 13.2 v as in specs) it is not ideal for long battery life, because your battery will never be charged to its full capacity. A higher quality bcdc charger will have a 3 stage charging profile which will contribute to better battery longevity. AGMs do not like to be underbonet because of the temps there so your choice of a lead-acid under bonnet is best.
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Follow Up By: Nomadic Navara - Sunday, May 02, 2021 at 10:52

Sunday, May 02, 2021 at 10:52
That device from Sidewinder will give you less charging voltage than your Patrols alternator. It is just a regulated power supply. If you are not going to invest in a propper DC-DC charger then use your old device.
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Reply By: Member - Siringo - Saturday, May 01, 2021 at 11:54

Saturday, May 01, 2021 at 11:54
Thanks everyone for the help. The vehicle is a 2013 Patrol 3 litre.
I've found a few AGMs that say they can be fitred under bonnet. 1 is from SSB. The names of the others elude me at present.
AnswerID: 636220

Follow Up By: RMD - Saturday, May 01, 2021 at 15:42

Saturday, May 01, 2021 at 15:42
Most AGM batteries do not like heat, hence the under bonnet precaution and excessive charging. If under bonnet, AND MAYBE claimed to be OK, then you have to consider both the underbonnet heat input and the charging heat input as additive of all heat applied to the battery. WHERE the battery is in the engine bay also has a large bearing on the above, Near/at front of engine bay is far cooler than at the rear of engine bay, ie, up in the corner where heat soak is maximized. On the turbo side of the engine bay is not a good place because of radiant heat, turbo do get warm sometimes. Many 70 series Toyotas had shorter life spans with their normal wet cell start batteries because the battery WAS up in the corner and failed from heat stroke. Operated in hotter climates makes the whole equation even worse.
All your choice of course.
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Follow Up By: Dennis Ellery - Saturday, May 01, 2021 at 23:34

Saturday, May 01, 2021 at 23:34
It would be wrong to say that all AGMs are not suited for under bonnet use.
A Century Dual Force AGM is specifically designed for 4WD under bonnet use.
I have two in my 70 series V8 diesel Troopy.
Optima is a spiral wound AGM that also works well under the bonnet.
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Follow Up By: AlbyNSW - Sunday, May 02, 2021 at 08:00

Sunday, May 02, 2021 at 08:00
I have used the under bonnet rated SSB AGM battery and they have given me 4 to 5 years of life. I am now on my second one
If that is the best place for your battery I wouldn’t hesitate to fit one, no doubt they would last longer in a cooler environment but I am happy with the compromise
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Follow Up By: Member - Bigfish - Friday, May 07, 2021 at 05:34

Friday, May 07, 2021 at 05:34
My SSB AGM lasted 13 months under the bonnet. I got 3 years out of 2 identical ones in the cars rear tub before I removed and went lithium. (still had lot of life left when I sold them cheap as second hand batteries. ...heat is no good for longevity!!!.
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Reply By: Member - Cuppa - Sunday, May 02, 2021 at 08:55

Sunday, May 02, 2021 at 08:55
I understand that you want to save money, but whilst going cheap on initial costs means less money spent now, it won’t save you money in the long run.

With any battery charged only via a VSR & under the bonnet expect a max battery life of up to 5 years. (But quite possibly less).

Taking the battery out of the heat & having it in the car may increase it’s life a bit, but if inside the car with you - ensure it is AGM, not a wet battery.

If using a VSR & under bonnet battery, I see no advantage in spending any more than you have to on a battery. A cheapie will get you a battery life much the same as a more expensive one.

A good AGM inside the car, looked after(ie. not regularly discharged below 50% & charged back to ‘float’ every 24 hours) with a smart charger should have a lifespan of 10 years+.

Batteries are expensive.

I don’t know the ABR dc to dc product, but offer a couple of considerations. A lot of cheaper dc to dc chargers are low amp outputs. Commonly 10amps or thereabouts. They will take a far longer driving period to recharge the battery so may not be effective, I recommend a minimum of a 25amp output. Also temperature compensation is a very desirable feature which is a significant aid to long battery life.

There are two commonly available types of smart chargers - dc to dc & solar regulators. If you have solar then the use of a VSR to charge whilst driving, & solar to top up the battery to 100% (which the alternator never will in day to day driving of a battery supplying regular loads) is a valid & workable solution for less initial cost than a dc to dc charger, providing you either stop driving early enough each day to set up portable solar to give it enough time to do the job, or if you have roof mounted solar which works all the time in conjunction with a VSR.

At the end of the day, a VSR alone will work, but will give you less available overnight battery capacity (from the same size battery which has been ‘smart charged’ but it may still be ‘enough’ to meet your needs). A valid path to take, but just buy a cheap battery - even just another starter battery - & expect to replace it far sooner.
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