AGM batteries

[superboots]

I am thinking of replacing my aging batteries with AGM type. Has anyone had experience of these. Lifeline is the brand leader but Delco have started selling this type now. I am thinking of going for 3 255 amp/hour batteries but I will then have a problem with the alternator. Apparently these batteries suck the juice until they are full and can fry most alternators. Bosch tell me their 140 amp alternator won't fry but is this hyp or will any large alternator cope with the demand?

 

[ean_p]

Me thinks that your battery will take what the alternator will give it....without damage to the battery or alternator....unlike wet and gel batteries that are very limited in the level of charge currant that they can accept...before they suffer damage. The problem with our AGM (Hawker Powersure) batts is that the voltage supplied during charging is very critical and has to be maintained at a constant level....unlike wet and gel batts which vary the voltage level in order to control / enable charging. I would look into this and see if your present charging equipment is suitable.

 

[pvb]

Alternators...

You don't say what alternator you have at the moment, but AGM batteries won't "fry" the alternator - always assuming that your engine compartment ventilation is reasonable. AGM batteries are effectively the same chemistry as wet lead/calcium batteries, and the charging current they'll accept will depend to a large extent on the depth of discharge they're subjected to.

I have a 660Ah bank of lead/calcium batteries and the most current I've ever seen is around 100A, using a 130A alternator and an Adverc regulator. If you are going to get a bigger alternator, bear in mind that the 100+ amp versions tend to be large-case units, which are very big and heavy, and require sturdy brackets. After bracket failures, I downsized to a 90A small-case alternator, with no real disbenefits in terms of charging.

One idea which is worth considering is to duct the air intake into the engine compartment so that it blows on to the alternator - in this way, you get some extra degree of cooling.

 

[HaraldS]

Re: AGM batteries - Frying Alternators

You will only fry an alternator if it isn't able to deliver full load for a longer time. The only difference with a big bank of AGM batteries will be that they will remain below the levelling off voltage for a longer time and thus take more charge faster. Ususlly with AGM you can also set that level a bit higher.

There are alternators on the market that cannot deliver full load for an extended amount of time. My original one was of that type and it made no more than 150 hours. In my case it was a Balmar that squeezed 100 Amps at 24V out of a small housing. Apparently several of those failed and my yard then switched to a same size Amptec that would deliver an honest 70Amps and not burn.

I changed to a bigger 135A Amptec and I'm very pleased with it. I'm also thinking of switching to AGM in a year, though my cheap semi traction batteries show no sign of aging. I currently have 6*140Ah giving 420Ah at 24V and they take charge very nicely, I charge at about 40A per battery. Often it goes at that level for almost two hours.

If Bosch says you alternator can deliver full load, which mean running at full exiting voltage for long periods, then you shouldn't be worried.





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[superboots]

Thanks for replies - not sure where this gets me. I have a delco 150 amp alternator stored on board - wonder if it will work or go up in a puff of smoke after an hour's work. Website not much good. Also is this US product compatible with european kit? How do I regulate it? AGM should not be charged above 14.1 volts. Anyone know about where to get secondhand Bosch alternators? I beleive trucks use 24 volts these days so not much use there

 

[HaraldS]

An easy precaution agaisnt frying the alternator, might be to get a regulator that senses alternator temperatur. Like for example the Balmar 612. It switches to half output if the alternator gets too hot. It also senses batterie temperature, so you can get closer to the limits with max voltage and charge faster, and it has settings for differnt types. AGM by the way can and should be charged at a higher volatge than GEL.

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[pvb]

AGM charging voltage...

It's not true that AGM batteries shouldn't be charged at more than 14.1v. As Harald points out, AGMs can be charged at higher voltages than gel batteries (which is maybe where you got the 14.1v figure from).

Most AGM battery manufacturers specify a bulk/absorption voltage of 14.4v, and you'll find that the "AGM" setting on most good battery chargers will result in this sort of charging voltage.

Whilst AGM batteries can be well suited to marine applications, I'd be cautious about keeping them in the engine compartment. AGMs can, in extreme circumstances, suffer from a phenomenon called "thermal runaway" which usually results in explosion. They are best kept in cooler places, and I'd suggest you should certainly use battery temperature sensors to control both your alternator regulator and your shorepower charger.

Your Delco alternator should be fine for your needs. It doesn't matter that it's a US product - volts and amps are universal. To regulate it properly you need to add a smart regulator. I'm very fond of Adverc regulators, but as AGMs need a more carefully controlled float voltage you might be better off looking for a 3-stage regulator such as those from Xantrex or Balmar.