auxillary battery on alternator booster diode

Submitted: Sunday, Nov 24, 2019 at 23:47
ThreadID: 139353 Views:1089 Replies:5 FollowUps:12
I need to replace an auxillary battery in the ute tray & am hoping for a maintenance free one. It is mainly for a fridge mainly - not to start the vehicle. A DC-DC charger may be better, though because it's the vehicle that comes as part of my job, don't want to add much accessory to it. So I have an alternator booster diode, though remove it if doing long highway runs. I'm looking for recommendations of what battery to buy. Is it worthwhile spending the extra on a gel battery over an AGM one?
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Reply By: Member - shane r1 - Monday, Nov 25, 2019 at 09:01

Monday, Nov 25, 2019 at 09:01
G’day
Any of the known brands in an AGM would do the job.
I understand the booster diode, but are you also running a voltage sensitive relay?
Cheers
AnswerID: 628786

Follow Up By: Cybermike - Monday, Nov 25, 2019 at 10:10

Monday, Nov 25, 2019 at 10:10
Yes I have the basic Redarc voltage sensitive relay. About the battery type - I heard that the gel option may be less damaged than the AGM by feeding it a voltage that is less than ideal.
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FollowupID: 903341

Follow Up By: RMD - Monday, Nov 25, 2019 at 11:10

Monday, Nov 25, 2019 at 11:10
Cybermike
If using a boost diode it has to be a Non smart alternator. If you need the diode in a normal alt system, is it being used to create compensation for a sickly low voltage regulator, ie, bringing the voltage up to normal which is then suitable for an AGM anyway. Any AGM needs around 14.4v and with a boost fiode creating that voltage all is normal, isn't it? Do you have a digital voltmeter on the aux battery to monitor what it is receiving ?
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FollowupID: 903342

Follow Up By: Cybermike - Thursday, Nov 28, 2019 at 00:52

Thursday, Nov 28, 2019 at 00:52
Reading 14.09v at engine idle the auxillary battery in the canopy. I'm guessing would be about 14.3v at normal driving revs. It was about 0.4v lower befor I fitted the alternator booster diode.
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FollowupID: 903373

Reply By: Notso - Monday, Nov 25, 2019 at 10:02

Monday, Nov 25, 2019 at 10:02
I reckon you are better off buying a 12 volt to 12 volt charger.

Fit this on your battery box and it can move with you when you change vehicles. This way you don't need a VSR as most of them have it built in.

12 Volt Redarc DC to DC with battery isolator

Or Projecta Charger
AnswerID: 628788

Reply By: Dave B18 - Tuesday, Nov 26, 2019 at 13:55

Tuesday, Nov 26, 2019 at 13:55
DC/DC charger can be fitted right next to the battery, and does not need to be a permanent fixture.
GEL batteries are definitely not more suitable, and are the most easily damaged battery.
Playing around with sub-standard charging options on an AGM battery, don't expect good life from the battery.
Use a quality DC/DC charger like the Ctek D250S or Projecta that are temperature compensated.
AnswerID: 628806

Reply By: Phil G - Thursday, Nov 28, 2019 at 09:49

Thursday, Nov 28, 2019 at 09:49
I think your current setup will kill an AGM battery in quick time.
You have no limit on the charging current. Most AGMs have a limit of 25-30A, which can be easily doubled with your setup. If you exceed this limit, they lose capacity until they become useless.
I had an AGM die within 12 months in a 79series canopy because it was simply charged through a Redarc isolator (no booster diode) and I could measure 46 amps going into it.
Simple solution - fit a 25A DC-DC charger for single battery or 40A for double battery. I have both Ctek D250S and Projecta IDC25 and both work fine.
AnswerID: 628827

Follow Up By: Cybermike - Thursday, Nov 28, 2019 at 10:20

Thursday, Nov 28, 2019 at 10:20
Thanks. Are there any other batteries that could handle life without a DC-DC charger? The starting battery is a sealed (wet?) battery that has lasted well being fed through an alternator booster diode. Maybe there is a deep cycle of similar chemistry?

At the moment I am the custodian of this company car which could be ‘borrowed’ by another employee, but still want the auxiliary battery for running the fridge on the weekends. I’m just trying to avoid investing much in portable equipment before I get my own vehicle.
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FollowupID: 903381

Follow Up By: Frank P (NSW) - Thursday, Nov 28, 2019 at 10:34

Thursday, Nov 28, 2019 at 10:34
The Supercharge AllRounder is a maintenance-free, wet dual purpose battery that others have reported on favourably, as have I.

According to my local Supercharge retailer, the AllRounder, because it is a wet battery, will accept without damage the currents that occur in a simple solenoid-controlled dual battery system. He said max charging voltage should be 14.4V. In another post you said you thought you had close to that.

My suggestion would be to go with one of those, and if budget is a factor, they are not outrageously expensive.
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Follow Up By: Allan B (Sunshine Coast) - Thursday, Nov 28, 2019 at 10:42

Thursday, Nov 28, 2019 at 10:42
Frank,

I also think that a hybrid battery ( AllRounder etc) may suit Cybermike's preferences.
But I think it should be described as flooded rather than "wet"?
Cheers
Allan

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Follow Up By: Frank P (NSW) - Thursday, Nov 28, 2019 at 12:17

Thursday, Nov 28, 2019 at 12:17
You're right, Allan. Flooded is the correct terminology.

Cheers
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Follow Up By: Allan B (Sunshine Coast) - Thursday, Nov 28, 2019 at 12:58

Thursday, Nov 28, 2019 at 12:58
.
Yes Frank, I guess all lead-acid batteries are "wet" in one manner or other, but flooded refers to those with free liquid electrolyte and differentiates from AGM type with the electrolyte absorbed in a fibre-glass mat.
I know that you understand that but it was for those who may wonder what we are on about.
Cheers
Allan

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Follow Up By: Frank P (NSW) - Thursday, Nov 28, 2019 at 13:25

Thursday, Nov 28, 2019 at 13:25
Absolutely, Allan. It is another example of the importance of correct terminology, rather like the threads about weight-based speed limits. Or should that be mass-based speed limits? OMG!!!

LOL
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Follow Up By: Allan B (Sunshine Coast) - Thursday, Nov 28, 2019 at 13:42

Thursday, Nov 28, 2019 at 13:42
.
Well Frank, I guess that it matters if the said vehicle runs over your foot (weight) or hits you at speed (mass), eh?
Cheers
Allan

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Follow Up By: Phil G - Thursday, Nov 28, 2019 at 17:39

Thursday, Nov 28, 2019 at 17:39
Cybermike, The crank battery would fare OK because it is flooded wet cell and because it is not being cycled. You stated the auxillary will be in the tray. An Optima is only AGM I know of that might fare well with unrestricted current while being cycled.
The only downsides to the Optima are that the capacity is only 75Ah for a 12" battery and of course they are a bit more expensive.
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FollowupID: 903398

Follow Up By: Cybermike - Sunday, Dec 01, 2019 at 04:06

Sunday, Dec 01, 2019 at 04:06
The battery I am replacing is an Optima Yellow Top that I’m not sure gave a fair life because of the low voltage it was getting before fitting the alternator booster diode. Yes, these batteries have a low capacity on paper, though from what I’ve heard can be taken down to a lower depth of discharge, versus the 50% generally recommended for other types.
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Reply By: Paul W33 - Saturday, Nov 30, 2019 at 21:06

Saturday, Nov 30, 2019 at 21:06
I bought my 76 series with a Diode and VSR and it had an AGM installed. Almost 3 years later everything going good, really happy with the set up, can't say how old the battery is as the label is a bit second hand but it a 105a AGM.

I have had a fridge running almost constantly over that period.
AnswerID: 628897

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