2010 Prado dual battery

[was44 Lurker Find all posts View Profile Close was44]

We have a 2010 Prado GXL and want to put in a dual battery system. We have been told that it is not that simple as there is not enough charge in ault to charge both batteries. Has any one got any ideas. was44

[rob127 Lurker Find all posts View Profile Close rob127]

Re: 2010 Prado dual battery

I have had a pirana system installed into a diesel, and it works fine. I run a third battery on camper trailer that also charges just fine

[LeighW Avid PP Poster! Find all posts View Profile Close LeighW]

Re: 2010 Prado dual battery

Hi,

I sell a Voltage Booster which will overcome the charging problem, see accessories 150, dual battery system.

Cheers

LeighW

[Kaosad Lurker Find all posts View Profile Close Kaosad]

Re: 2010 Prado dual battery

Hi guys, an alternative to voltage boosters when fitting dual battery systems is to fit a redarc dc to dc charger. I had the usual issue and ditched my voltage sensitive relay as it wasn,t reaching switching voltage. The Redarc unit takes the standard alternator output and digitally ups the voltage and current up to around 14.9 volts and 21 amps at idle to the second battery! As the second battery gets closer to full charge, it drops back and when it reaches full charge, the charger goes into "float" mode to maintain the battery. This is beneficial to your second battery as it reaches 95-98 % capacity as compared to 80- 90 % that the alternator gets it to. It has an ignition sense wire that only turns it on when the start battery is at a safe level, but unlike a voltage sensitive relay, it comes in at around 13 volts not 13.8. The unit sells for around $490+ but is definitely woth it.

[drivesafe Senior Member Find all posts View Profile Close drivesafe]

Re: 2010 Prado dual battery

Hi Kaosad, and sorry but that’s a gross misrepresentation of the facts.

For a starter, why will an alternator only charge a battery to 80-90%. If the voltage being applied to a battery is higher than the voltage of a fully charged battery, which is 12.75v, then the battery will be fully charged to at least 95%.

So even if the vehicle’s voltage is just 13.2v, that’s still nearly half a volt higher than that required to get a battery to a fully charged state.

Where there is an advantage is that the higher the charge voltage, the quicker the battery will charge, but even here your info is misleading.

While an alternator may only charge at 13.2v and while any brand of DC-DC step up can raise the voltage higher than 13.2v, contrary to your comments, these devices can only raise the voltage higher as the battery approaches a fully charged state.

So if the battery is in need of topping off, then a DC-DC step up will fully charge the auxiliary battery quicker than your alternator.

But if you have a 100 Ah AGM auxiliary battery and your take it down to it’s limit of 20%, your DC-DC step up device will NOT be charging at 14.8v, it will be more like 13v if it’s lucky.

Furthermore, it will take around 5 hours driving time to fully charge the battery and in 5 hours driving time with an alternator voltage of 13.2v you will get the battery to about 90-95%.

So for an investment of nearly $500 you get a gain of just 5-10% over what your alternator can do.

For a hell of a lot less money, you could use a 120 Ah battery and while the alternator would charge still charge to about 90% in 5 hours driving, your DC-DC device would do no better because a fact that is ALWAYS neglected when talking about these converters, and that is that the charge time is very much time based and the lower the battery the longer the drive time needed and if was44 found that his single auxiliary battery was not big enough or if he buys a caravan or CT and needs to charge even more batteries, then your DC-DC converter will be an absolute disaster for him.

For every 20 amperes used, you need to drive for AT LEAST one hour when using a DC-DC converter, this does NOT apply when using your alternator, and an alternator replaces the bulk of the used battery capacity in the early stages of any drive time while a a DC-DC converter does not.

Using rob127’s set up as an example, if he starts his drive with two low batteries, he could easily up to 50 amperes of used battery capacity in the first hour and another 20 amperes in the second hour, but a DC-DC converter would need nearly four hours to do the same thing.

Now while the charging of batteries by an alternator means the charging tapers off rapidly as the battery’s SoC rises, so the charging current reduces rapidly, but after 4 hours drive, rob127’s alternator will still have replaced far more of his used battery capacity than your DC-DC converter would have a hope of doing.

There is a lot more to it but the way these DC-DC converters are being marketed is based only on their glossy points and not on the full facts.