Flat Plate V Spiral (Optima), DC/DC v Parallel Charging

Submitted: Tuesday, Sep 06, 2011 at 18:03

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Stan2.8D

Need some help with a final decision on my batteries etc as I cant make out what is just marketing from sales people and what is people's real experience with this. Thanks

Battery for fridge etc no cranking.
Alternator charging only at the moment may put in a solar panel later.
So need faster charging with less driving.
Lots of corrugations where I live.
Would like battery longevity ie more than 2 or 3 years.

Looking at the Optima D31A 75Ah X2 @$368 each
Century c12-100da AGM 100Ah X2 @$288 each

Do the Optima's really charge faster, last longer, and are less affected by vibration or is it all marketing. Am I better with lower Ahrs but with a faster charge and a longer lasting battery?

Ctek DC DC D250S Charger: Is this worth the $250? Will it charge the Optima's faster and fuller or will it make little difference.

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Reply By: allblack55 - Tuesday, Sep 06, 2011 at 18:59

Tuesday, Sep 06, 2011 at 18:59

Hi Stan,

I`ve been through this very exercise recently and sympathise with your quandry.
Suggest you Google the topic as there are lots of entries on U.S. sites, you can even contact the manufacturers and they will address your technical enquiries extensively.

In the end I decided to continue with flooded Century N770 under the bonnett, all batteries require some maintence. Similar CCA rating Optima have less reserve capacity and are heavier to boot. There are also charging issues using a smart charger if the PD is taken low by utilising 100% the claimed capacity, use of the vehicle alternator obviates this problem.

It`s the old story"horses for courses" and you will find there are several AGM batteries of similar price/specs (and more expensive ones too) available.

Given their cost in Oz and the warranty offered I couldn`t justify the outlay based on my research and requirements.

If you would like a more details that flavoured my choice mail direct sunelectronics@bigpond.com

Regards,
Leigh.

AnswerID: 464375

Reply By: Member - Captain (WA) - Tuesday, Sep 06, 2011 at 18:59

Tuesday, Sep 06, 2011 at 18:59

Hi Stan,

The Optima are a spiral wound AGM battery that has a stronger construction with its pressure valves are set at 40psi. The flat plate AGM (Century etc...) have their pressure valves set at 2-5psi, a lot lower. Simplisitically, the pressure allows the hydrogen and oxygen produced during recharge to recombine. If charging is too high, the hydrogen/oxygen will be produced faster than it can recombine, hence will cause the valves to vent and battery capacity will be lost.

The Optima with its higher pressure can handle much higher recharge rates and are also less prone to vibration due to their stronger, spiral construction. But "normal" AGM are also good for vibration resistance too when compared to a wet cell.

Most AGM's can be charged at ~25+ amps, so choosing the Optima vs Centruy on that basis alone means both are the same.

Charging a battery properly is key to long life, so a dc-dc multistage charger will help significantly. Virtually no van/vehicle has wiring big enough to properly charge a battery to 100% (many caveats here) and this is one reason batteries die prematurely.

AGM's are more prone to heat issues and do not like underbonnet applications. I prefer wet cells in an engine bay and AGM's in a van (or away from heat in rear of vehicle etc...) but many people install AGM's underbonnet and have success.

By keeping the SoC (state of charge) greater than ~50% you will improve battery life. If you regualry run your battery too low (<12V), then life will be less. So getting a higher a/hr will improve SoC for a given load.

I assume you are installing in a van, if so IMHO the Century AGM would suit your purpose better (as well as being cheaper) as it has a higher a/hr and can still easily handle the 25A charge the Ctek dc/dc charger will produce.

Cheers

Captain

AnswerID: 464376

Reply By: Travis22 - Tuesday, Sep 06, 2011 at 19:19

Tuesday, Sep 06, 2011 at 19:19

This is my short answer.

AGM batteries will charge faster then a Wet cell ie. Calcium/ Calcium lead acid battery.

Given you are looking at two AGM batteries the difference wouldnt be noticeable in the real world IMO. It comes down to internal resistance so if you want to look up the figures you could work out exactly what the difference is but again IMO the Optima wouldnt be that much better. (Im guessing minutes, not hours difference like you might see when comparing AGM > Lead Acid type. But there are other variables, namely alternator voltage and current output.)

In terms of longevity again, both AGM's will last a similar term. The BIGGEST killer of AGM batteries is heat. Put them in the engine bay and you do risk shortening their lifespan.

IMO bigger is better, the difference between the above two in practical terms is going to be an extra day without running the vehicle with the fridge plugged in.

No car battery is going to recharge back to 100% off the vehicles charging system, work off around 90-95% so IMO it is a good idea to recondition / recharge batteries at home or on the road when you have 240V on a good smart charger like the Cteks after a long trip where the battery(s) are constantly cycled.

I wouldnt buy a Ctek at the RRP but the prices on Ebay and the like are much more reasonable.

I assume you are wanting to charge an axillary battery some distance from the alternator ie. camper trailer / caravan???? In which case yes, a DC-DC charger is a must unless you have solar or generator power to recharge said battery.

Will a DC-DC charger charge the rear axillary battery faster / fuller... Again, depending on your situation, you dont have any other choice. The voltage drop from your alternator all the way back to batteries in a CT/ Caravan will result in said battery basically getting no charge.

But perhaps i shouldnt assume! If you do not have a CT/ Caravan, then generally speaking no you do not need a DC-DC charger. I have my auxillary batteries in my ute tray, just under 5m total cabling. With heavy gauge wire VD is not an issue.

Again i would go with the larger battery. Any difference in the recharge rate between the two AGM's is going to be insignificant so at the end of the day the battery with the higher capacity will always have more Ah left in it which again = more time / another day at camp without running the vehicle.

If you want to get really really really picky then we would need to know your exact application / use for the batteries. How low are you going to take them (what will be their load) and then how much driving are you able to do and how often?

Travis.

AnswerID: 464379

Follow Up By: Travis22 - Tuesday, Sep 06, 2011 at 19:23

Tuesday, Sep 06, 2011 at 19:23

Geepers! Two other guys answered before me in the time it took me to reply!

All good answers, and i think we are all saying much the same.

Travis.

FollowupID: 738296

Reply By: Stan2.8D - Tuesday, Sep 06, 2011 at 20:04

Tuesday, Sep 06, 2011 at 20:04

Thanks guys.
The AGM's will go in the bed box in the Delica (van).
I can drill some holes in the box next to the batteries or they could be vented out of the floor with tubing I suppose.
If the flat plate vent at a far lower psi, is there a greater need to vent them to outside/or should all AGM's be vented to outside when used in an enclosed area such as this?

AnswerID: 464383

Follow Up By: Member - Captain (WA) - Tuesday, Sep 06, 2011 at 20:32

Tuesday, Sep 06, 2011 at 20:32

Hi Stan,

When venting a battery box, it is best to vent "high" as the hydrogen is lighter than air and will be on top. Some AGM batteries have a central collection port to vent directly from the battery to outside, but I don't think Optima or Century do this, so you should vent the box (be careful of allowing dust in!)

In the unlikley event of an AGM venting, neither would be preferable as while the Century is at a lower pressure, it will relieve less. If an Optima vents, it will be at a much higher pressure hence more volume.

In your situation (away from engine heat, possibility of high alternator amp charging) it would be very unlikley to occur and I would not get too hung up on it. Manufacturer advice several years ago was that AGM batteries did not need venting, but this is not the advice now.

While an Optima is technically a "better" battery, it is IMHO not the best value for $$$. It has specific advantages that you are not really requiring. One is they can charge at ~100A rates, unlike flat plate AGM's and your setup sounds like it is not capable of this high recharge rate.

Keep an AGM cool, stay above 50% SoC and recharge ASAP with a multistage charger and you will get many, many years (>>5) of service. Most good AGM's are capable of 10 years service in these conditions.

Cheers

Captain

FollowupID: 738303

Follow Up By: Stan2.8D - Tuesday, Sep 06, 2011 at 21:39

Tuesday, Sep 06, 2011 at 21:39

When I vent the bed box does this has to go outside the van?
If so it really can only go via a pipe through the floor as I dont want to drill a hole in the side of the van.
The Delica has two whopping dual sealed cranking batteries (they do that in Japan apparently),
so I am guessing the alternator (90amp) will struggle with another 2 batts in the back.
Would the DC DC charger help this as the jury seems to be out on getting one at the moment?

Many thanks for your help.
Stan

FollowupID: 738319

Follow Up By: Member - Captain (WA) - Tuesday, Sep 06, 2011 at 22:15

Tuesday, Sep 06, 2011 at 22:15

Hi Stan,

I would not get too hung up on venting the box. I cannot advise you not to do it, but my battery box is large and does not vent to the outside - enough said! (size and potential volume of gas taken into account).

A 90 amp alternator is actually quite large. Starting a vehicle takes next to no power at all, the starter runs at say 300A for 2 seconds, thats only 0.2a/hr so you can see its inconsequential - from an a/hr point of view. If your starter batteries are fully charged, then recharging them after starting the vehicle will only take seconds (actually, not quite true, but the point being it takes minimal power from your alternator and illustrates what I am trying to say).

So, you still have all 90 amps to recharge your new AGM batteries - but you will only be using ~25A with the Ctek. That means your alternator has ~65A to spare (runs your lights at night, fuel pump etc...). Point I am trying to make is that your 90A alternator should do this easily, the only exception is if you have a huge amount of spot lights for night driving.

If you want the best life from the AGM batteries, then the dcdc charger will be a worthwhile investment. Making some assumptions here, your alternator will be able to recharge the batteries to ~85% SoC, but will struggle to get higher for many reasons. 100% recharge is possible from alternator charging, but you will need BIG cables and a long driving time.

Now if you already have a decent multistage 240V charger, then if you only rely on the alternator a few times to recharge the batteries "fully" then no problem and there will be minimal effect on battery life. But if you are away from 240v for extended times (greater than week/s) and stay at low SoC, this will adversley affect battery life.

Even with a dcdc charger, you will still need a reasonable driving time if your battery has a low SoC. While you get 25A charging initially, it tapers off at ~90% SoC but the voltage then increases to "fill up the battery" - this is what the alternator cannot do.

Cheers

Captain

PS. I have simplified some concepts so not 100% tecnically correct for some explanations, but it hopefully does explain the concept.

FollowupID: 738324

Follow Up By: Stan2.8D - Tuesday, Sep 06, 2011 at 22:32

Tuesday, Sep 06, 2011 at 22:32

Many thanks: I think I am almost there with this.

I am thinking of getting 2 slightly larger batteries to compensate for Ah capacity loss due to being unable to fully recharge and fully discharge. The larger Century flat plates (120Ah/125Ah)will take up to 36amps charging rate. The 100Ah will take up to 30amps.
The DC DC charger seems to be a good idea but it seems to be self limiting with a 90amp alternator and batts which will take a charge up to 36amps, to fit a charger which will limit to 20amps. I presume that a higher rated charger will charge quicker than the 20amp charger. If so, any recommendations?

I wont be fitting the van with 240v input (but may have to if this is an issue) and will likely be away from 240v for several weeks at a time. Will be relying on alternator charging and a vague possibilty of solar later on but not convinced on that for lots of reasons. Will the DC DC charger assist in compensating for long periods of alternator only charging?

FollowupID: 738328

Follow Up By: Member - Captain (WA) - Tuesday, Sep 06, 2011 at 23:20

Tuesday, Sep 06, 2011 at 23:20

Hi Stan,

Simplistically, you need to put back in what you take out. Getting more batteries will not help you put back in, it will only delay how long you can keep taking out for.

Also, having a ~95A alternator doesn't mean you can recharge at 95A. There are many reasons why, but you will be very unlikley to charge at more than 15A to a rear mounted battery, the size cables needed for this will be very large and their cost will virtually buy a dc-dc charger!

But having two batteries (if you can fully recharge them) is good as it increases the SoC for a given load. The longer you stay put, the more batteries you will need to maintain a decent SoC, or run the vehiicle to recharge, or go solar!

A 100a/hr battery at 50% SoC will give 50a/hr, about what most people use a day - give or take a bit. Go lower than this and you strt affecting long term battery life. How long do you intend to stay put? (I know, how long is a piece of string!) This will help decide whats the best way, but then the best is not the cheapest!

The way I see it, you have several options;
1. one AGM, alternator charging - will be cheapest but will likley have the battery struggling to last more than 2 years - but cost effective!

2. one/two AGMs, dc-dc charging - will give good 100% recharging (if you drive ~3-4 hours) and should give good battery life. But you will be limited to 2-3 days between driving for recharge.

3. add solar and depending on how many panels, increase to 5+ days before driving (if sunny!).

4. add a generator to account for cloudy days.

I have been thru all the above steps over time and in that order. I have 2 x 120a/hr AGMs, 40A dc-dc charger, 160W solar with MPPT controller and a Honda genny.

From my experience, getting the dc-dc charger was perhaps the best move as my type of camping is moving on after a few days. Adding the solar makes a 5-6 day stay possible without any motor running (sun dependant) but after that i need to run a motor, either the vehicle or the genny. My power consumption is ~80a/hr day, but I have a party of 4 and am a relatively big power consumer.

Trying to read into what is most cost effective for you would arguably be a dc-dc charger on a single AGM battery. If you can get a second AGM, even better. Hopefully I haven't confused you further!

Cheers

Captain

FollowupID: 738331

Reply By: TerraFirma - Tuesday, Sep 06, 2011 at 20:17

Tuesday, Sep 06, 2011 at 20:17

AGM Batteries and Ctek charger is a winning combination. Ebay is the go for 25AMP Cteks for as little as $260 without the crocodile clips. The Ctek chargers are the best, spark free, with 8 modes including re-conditioning. You don't have to buy Optima for your application. Other brands such as Fullriver make an excellent DC Series AGM battery.

AnswerID: 464385

Follow Up By: Stan2.8D - Tuesday, Sep 06, 2011 at 20:21

Tuesday, Sep 06, 2011 at 20:21

Is that a Ctek charger for mains charging or DC DC alternator charging?

FollowupID: 738301

Reply By: Member - Phil G (SA) - Wednesday, Sep 07, 2011 at 00:03

Wednesday, Sep 07, 2011 at 00:03

Gday Stan,

For the conditions you state, Optima is the winner.

Big difference is the max charging rate. With Optimas there is no limit. With the C12-100DA Century AGM (and most similar AGMs) you are limited to 30Amps (see their spec sheet). If you have good wiring, you can easily put 50 amps into that battery from an alternator at 2000 rpm.

If you fit the Century AGMs then how are you planning on limiting the current? The Ctek DC-DC charger will limit the current to 20Amps which will prevent you from getting the quick recharge you want from your alternator.

Optimas have been around for a long time and it is very rare to hear a bad word about them. I'm running a 55Ah Bluetop thats 8 years old, but had an easy life, but it still runs an Engel for 2 days straight. I killed a Remco AGM (identical to the Century AGM) in under 3 years by charging it straight off the alternator.

Cheers
phil

AnswerID: 464400

Follow Up By: Stan2.8D - Wednesday, Sep 07, 2011 at 00:07

Wednesday, Sep 07, 2011 at 00:07

Thanks Phil,
Its because of your previous post that I have been seriously considering the Optima for the last day or two, but as you can see people dont seem to think that the Optimas will charge any quicker than flat plates.
What you say makes sense but I just dont know who is right as this is all new to me.

FollowupID: 738334

Follow Up By: Stan2.8D - Wednesday, Sep 07, 2011 at 00:21

Wednesday, Sep 07, 2011 at 00:21

Im guessing here that the issue is not so much the maximum charge rate but the type and length of wiring. Captain says the max from my set up is likely to be 15amps into a 20amp charger and 30amp rated battery. Phil says I could potentially produce 50amps into an unlimited battery presumably without need of a DC DC charger but this would require upgraded wiring.

Did I get this right?

Phil's set up would cost quite a lot more as it would require maybe 2 or 3 Optima's but could potentially cut charging time by 2/3rds.
The flat plate option would give me greater Ahour storage capacity but the greater the capacity, the longer it takes to recharge especially if limited to 20amps.

FollowupID: 738335

Follow Up By: Member - jay D (VIC) - Wednesday, Sep 07, 2011 at 08:25

Wednesday, Sep 07, 2011 at 08:25

Redarc now make a 40 amp dc/dc charger. Mite also be worth a look.

cheers

jay

FollowupID: 738343

Follow Up By: Member - Phil G (SA) - Wednesday, Sep 07, 2011 at 08:37

Wednesday, Sep 07, 2011 at 08:37

Gday Stan,

The numbers I give are one's I have measured. I don't believe anything unless I've measured it.

For the 3rd battery in the canopy (similar situation to your Delica) I run 4Ga cable for both pos and neg, a Redarc isolator, fusible links at each end. I measure current with a digital clampmeter. Alternator is the standard 110A Landcruiser alternator. My earth lead goes to both the motor and the cranking battery - important if you want to maximise charging current from the alternator.

When the 100Ah Remco AGM was near new, I discharged it to 12.0V and measured current about 5 minutes after starting with my hand throttle at 2000rpm so the alternator's output was good. Current was 46amps. As the charge comes up on the battery the current drops exponentially. So after an hour, it might be 20+ amps, and after 2 hours, maybe 10+ amps etc etc

The Remco specifies a max "initial charge current" of 30 amps - same as the Century AGMs you are considering. I used to think this was purely because the battery could get hot if this was exceeded, so I put a temp probe on the casing and found the temperature never got above ambient. So I allowed this to be exceeded. After 2 years the AGM was underperforming, after 3 years the capacity was down to 20Ah and it was very slow to recharge because it was dead - I presume from sulphation. That battery was well looked after - never discharged below 12.0V and was topped up on a Ctek when not on trips.

I replaced it with an 8 year old 55Ah Bluetop Optima that my son gave me. Did the same measurements a few months back and have used it on 2 trips now to run one of my 2 engels. It performs very well - will run the Engel for 2 nights and I've measured 35 amps going into it under the same conditions as above. Even though the Ah are lower on the Optimas, I think the capacity is more usable - just like they claim.

I'm sure you will find either battery will suit your purpose well - you have done your research well and have narrowed it down to the 2 best choices for your situation. But if you are like me, and drive for 30 minutes or an hour during the day and want to get the most current back into your batteries, then you need nice fat wiring, good short circuit protection and a battery that can stand high charge currents.

Cheers
Phil

FollowupID: 738344

Follow Up By: Stan2.8D - Wednesday, Sep 07, 2011 at 09:07

Wednesday, Sep 07, 2011 at 09:07

"But if you are like me, and drive for 30 minutes or an hour during the day and want to get the most current back into your batteries".

Yup, that really is my main priority.. by far.

FollowupID: 738349

Follow Up By: Member - Captain (WA) - Wednesday, Sep 07, 2011 at 10:03

Wednesday, Sep 07, 2011 at 10:03

Hi Stan,

Phil is correct in that an Optima will take very high charge currents. However, this requires very large wiring. 4AWG cable is 20mm2 and assuming you have 14V available at the alternator, you still lose ~0.6v at 60A recharge over 6m cable length. Thus there is "only" 13.4V available for recharging - but this will quickly get charge your battery to ~85% SOC, then continue to get to 100% over a longer time.

But... it is very dependent on your alternator. My 200 only puts ut on average 13.2V, its temp compensated and as soon as the underbonnet warms up, it drops from the 14.3V to 13.2V quite quickly. Thus in my case under the above assumptions I would only have 12.6V to recharge, this would not work very well at all (some assumptions here for simplicity, but you get the idea). Its also why I had to go to a dc-dc charger and as many vehicles now come with temp compensated alternators, why dc-dc charging is becoming more important.

It would be wise to check your alternator output before deciding on your final setup, as I mentioned earlier, a lot depends on how you camp/drive as to what suits you. Measure both at start-up and then after a long drive when the underbonnet is nice and warm - you will be able to measure if you have a temp compensated alternator.

If quick recharge is your highest priority, then nothing charges quicker than an Optime IF you have suitable recharging setup.

While alternator recharging can produce very high recharge current if you use BIG cables, it still struggles to get 100% SoC as you need a higher voltage for the last ~10-15% of charge. Thats why I use a Redarc 40A dc-dc charger, it has a high recharge (40A), but also is capable of getting 100% recharge as its a multistage charger and boosts the recharge voltage for the final stage - it gets there quicker overall to 100%. Achieveing 100% SoC is required to get long battery life and if you have invested in Optimas, you want them to last.

Phil - your AGM probably died from overcharging. If yu exceed the max recharge rate, the oxygen/hydrogen produced during recharge cannot recombine quick enough and thus vents. As you cannot top up an AGM, you lose "water" and thus capacity is lost. Simply, you lost water from the battery and it started to dry out. As Optimas have significantly higher vent pressure, they can recharge at much higher rates as they can re-combine faster.

AGM's are very efficient at using the energy to recharge thus they rarely get hot - but if thermal runaway occurs, thats a different story - its also why AGM's can have issues when installed under the bonnet.

Cheers

Captain

FollowupID: 738356

Follow Up By: Member Al (Sunshine Coast) - Wednesday, Sep 07, 2011 at 10:35

Wednesday, Sep 07, 2011 at 10:35

Captain, That is the best description on this subject that I have seen anywhere.
And I endorse it wholeheartedly.

Cheers
Allan

Member
My Profile My Blog My Position Send Message

FollowupID: 738360

Follow Up By: Stan2.8D - Wednesday, Sep 07, 2011 at 10:52

Wednesday, Sep 07, 2011 at 10:52

Yes, thank you Captain and Phil: with your excellent posts, I have been able to make what I think is the best decision for my needs.

FollowupID: 738362

Follow Up By: Member - Phil G (SA) - Wednesday, Sep 07, 2011 at 11:23

Wednesday, Sep 07, 2011 at 11:23

Gday Captain,

My measurements are done with the battery in the canopy i.e. with the voltage drop taken in consideration. It was not on a bench. My voltage drop is as you suggest, about 0.1V for every 10 amps. I use a separate voltage measuring wire on each battery hooked up to a digital voltmeter in the cab - the voltage drop gives me a rough estimate of how much current is going into each battery.

In practice, with my setup, I haven't found alternator temp compensation to be an problem. The highest currents are being pulled after startup - when the alternator is cool. I expect Stan's Delica is similar to mine where it is rare to see the voltage drops below 13.6V.

Thanks for the explanation about the AGM drying up - hard to believe that it can be overcharged at less than 14V, but there you go!

Cheers
Phil

FollowupID: 738365

Follow Up By: Member - Captain (WA) - Wednesday, Sep 07, 2011 at 15:26

Wednesday, Sep 07, 2011 at 15:26

The most important thing is to get what works for you :) My 80 used to charge fine from the alternator, but my 200 is a different kettle of fish. Its all about horses for courses.

Phil, your setup works well for you and using the volt meter is a great way of inferring the amp reading.

Stan, I look forward to your post when its all done and how if the final product works for you.

And thanks Allan for your comments :)

Cheers

Captain

FollowupID: 738381

Follow Up By: Stan2.8D - Wednesday, Sep 07, 2011 at 16:10

Wednesday, Sep 07, 2011 at 16:10

Have ordered 2X Optima's 75Ah.
The 40amp charger is about $500 so if the only benefit for me when using a spiral is extra longevity from getting that last bit of top up, thats nearly the cost of 2 new batteries which I would rather not shell out for now. So if they go a bit sooner and I dont have to restrict my charging to 40amps then its not the end of the world.

My Delica is about 15 years old so I dont reckon the alternator will be temp compensated. I can upgrade to a 120amp alternator if the 90amp proves inadequate.
I have a good auto electrician here who will no doubt give me the best wiring set up he can and again I would much rather faster alternator charging than anything else, based on the types of travel patterns I expect to do and my disinclination to go solar.

FollowupID: 738385

Follow Up By: Member - Captain (WA) - Wednesday, Sep 07, 2011 at 20:00

Wednesday, Sep 07, 2011 at 20:00

Hi Stan,

Understand about the charger cost and yes, you are right, arguably not cost effective - leaves you with more money to get bigger cables to the batteries. Better not to use anything less than 20mm2 if you want a decent charge and even bigger will only help more.

One thing I have found hugely useful is a Nasa BM1 battery monitor. It tells you the amount of charge going in/out of the battery, the current SoC, and how much time remaining for 0% SoC or 100% charge (depending if you are charging/discharging at the time). While I have a volt meter, the difference in knowing exactly what you batteries are doing and their SoC is very comforting.

Anyway, thought I would find you something to spend your money on since you have saved $500 ;)

Cheers

Captain

PS. You won't regret getting Optimas, pricey but very good.

FollowupID: 738396

Follow Up By: Stan2.8D - Wednesday, Sep 07, 2011 at 20:18

Wednesday, Sep 07, 2011 at 20:18

I looked at the Nasa but I think I'm right in saying that it would only monitor one battery or two linked together.
I was concerned that I wanted to be able to monitor how both of the Optimas were charging in case one began to fail, I wouldn't be able to tell. The Nasa looks a great unit but it was also quite pricey and I didnt have time to order it from the UK.
Also looked at the the National Luna which can monitor 2 but was quite a bit more expensive than the ABR unit which also less bulky
It wont do % of charge or discharge but that's easily solved with a bit of paper and I reckon I will learn what resting voltage equates to in percentage, so I went for that one.

To get everything your Nasa does and to be able to monitor 2 separately, I think you are looking at a Xantrex etc and then you are talking serious money.

FollowupID: 738400

Follow Up By: Member - Captain (WA) - Wednesday, Sep 07, 2011 at 21:17

Wednesday, Sep 07, 2011 at 21:17

Yeah, the Nasa monitors the whole bank, not individual batteries - same as the Xantrex does. They both can monitor an additonal voltage source, I use mine to see what the incoming voltage is from my vehicle to the dc-dc charger. The Xantrex has additional smarts that can turn generators off/on as required and has external alarm outputs.

Monitoring the whole bank as opposed to individual batteries is a very small shortcoming IMHO, if the batteries were purchased together (same age), are wired properly and thus are installed as "evenly" as possible. I am unaware of any monitor that looks at indivudal batteries in a bank, apart from simply buying additional monitors.

There is a Nasa agent on the East Coast and they sell within ~$15 of the UK price. I would have purchased from them if I had of known at the time, it took ~2 weeks for my UK purchase to arrive, but was worth the wait :)

But you are right, an amp meter and a volt meter are far cheaper, the Nasa just has a chip to do all the hard work for you :)

Cheers

Captain

FollowupID: 738414

Reply By: Echucan Bob - Monday, Sep 12, 2011 at 15:13

Monday, Sep 12, 2011 at 15:13

The local price of $255 for the CTEK compares well withe the best US price of $200 plus postage.

The Nasa BM 1 is 85 pounds plus postage.

AnswerID: 464799

Reply By: Member - Matt M - Tuesday, Sep 13, 2011 at 14:02

Tuesday, Sep 13, 2011 at 14:02

Hi All,

Great discussion in this thread. Was a time when any mention of aux batteries, DC/DC charging or alternator charging would bring out the rabid element (I have been guilty). Don't post much nowadays, but still read a lot and this is one of the best (balanced) 12v threads I have read.

No one right answer, but some great simply explained options.

Thanks all.

Cheers,

Matt.

AnswerID: 464893