Battery Advice.

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Originally Posted by inside

Anyone on Aulro have thoughts on DCDC chargers? I await the responses. :sly:

I run two Optima 55ah batteries connected in parallel as a dual battery system. I'm happy with them and they work well. Anecdotally I believe they do charge quicker from the alternator as compared to my previous flooded lead battery.

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I was talking to my auto sparky the other day to get his opinion on what size cable I would need to run to the rear. He suggested I run a DC to DC charger.

By doing this I could run cable much thinner than I would otherwise. He also said that modern alternators don't put out the optimum charge volts and this also overcomes this.

So I am going to try one of these.

Ctek D250S Dual DC TO DC Solar Battery Charger 12V 12 Volt DCDC CAR AGM Caravan | eBay

As I run solar it is also good for this as it has an inbuilt solar regulator and if the aux battery becomes full it switches the solar to the starting battery.

A DC to DC charger will be able to boost the voltage to a higher value, however the time it takes to get a battery charged depends on the current you can get down the cable. With a DC to DC charger the current will be limited by the charger not the cable.

DC - DC chargers are quite slow aren't they? I have no experience with then but that does seem a limitation.

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Originally Posted by Mr Whippy

I was talking to my auto sparky the other day to get his opinion on what size cable I would need to run to the rear. He suggested I run a DC to DC charger.

By doing this I could run cable much thinner than I would otherwise.

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Hi Dave and this is one of the many con jobs used to sell DC/DC devices.

While most things powered by DC will reduce their current load as the voltage supplied to the device drop. Things like compressor fridges, lights and such but this is not the case with inverters.

As the voltage drops at the input of the inverter, to maintain the same voltage a current out, an inverter will increase it’s current demand.

With inverters ( converters ) like DC/DC devices, because they are not very efficient at what the do, they will increase there current demand quite substantially.

So by using thinner cable to supply power to a DC/DC device, you will dramatically increase the voltage drop and this in turn means a major increase in current demand.

This large increase in current demand means your alternator has to work much harder, and this means more energy being pulled from your motor and that all adds up to high fuel use and a more expensive drive.

So using thinner cable is a saving up front but the more you use the DC/DC device, the initial saving will soon be an additional running cost.

Also, if you go with the Optima Yellow Top, even the smallest 55Ah Yellow top can draw in excess of 60 amps, and that down 10m of 6B&S cable.

Even a 105Ah Allrounder will draw up to 35 amps while being charged off an alternator.

The lower the state of charge of the battery when you start your drive, the higher the current the alternator will supply.

So at the very time when you need higher charge current, when the is low battery, is when the alternator does it’s job.

Where as, with a DC/DC device, the lower the battery the longer ( much long ) the dive time has to be to get the battery to the same level of charge an alternator can achieve by itself.

Dave you are far better off charging your battery straight off the alternator.

Odyssey all the way , I had a few yellow tops they were ok but nothing beats 1400 cc .I been running a single odyssey battery in my previous truck and handled the winch/cranking/fridge power supplies tasks with ease.

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Originally Posted by manchild21000

Odyssey all the way , I had a few yellow tops they were ok but nothing beats 1400 cc .I been running a single odyssey battery in my previous truck and handled the winch/cranking/fridge power supplies tasks with ease.

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Which battery are you using? That current is much more than quoted for most automotive size batteries. Often the highest ratings are around the 800 to 1000 CCA. The battery blokes always make a lot of it when you tell them you have a diesel.

Its a 35-PC1400 .

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Originally Posted by manchild21000

Its a 35-PC1400 .

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That 1400 Amp is a 3-5 second pulse, not a standard measure for batteries, it is Odyssey's own Pulse Hot Cranking Amps (PHCA). Looking at some of the other more standard measures

Odyssey PC1400-35 /Optima D31A

Cost $475/$310
CCA 820/900
MCA 950/1125
PHCA 1400/????
Ah at 20 hour rate 65/75
weight kg 22.7/27.2
Dimensions: 240 x 174 x 221mm/325 x 165 x 238mm

On the brief analysis that can be done on the figures above the Odyssey is about 50% more expensive about 9% less CCA 15% less MCA, can't tell what the PHCA difference is as it is not quoted for batteries other than Odyssey batteries.

If you have limited space then the Odyssey might be a good choice. Might be worth looking at a similar size optima.

I don't know if I have missed something or over simplified it. Happy to consider other info.



Prices and data from Odyssey and Optima web sites you will have to pull down the optima battery handbook for the data.

Yep , that 3-5 sec 1400 crank made a difference in starting . However it was the ability to run a single battery system in the disco with space being premium and 2 failed Optimas that attracted my attention . Figures maybe nice on paper but mean nothing when the product fails.