Will the voltage booster maintain the protection provided by the original fuse that it replaces in the event of a fault developing in the vehicles electrics?

Yes, the MK1 uses fuseable links that will rupture the same as the original fuse and protect your vehicles wiring etc.

The MK3 version has two levels of protection, an electronic circuit breaker and a fuseable link. The first level of protection is the electronic circuit breaker that trips to protects the vehicles wiring, once the fault condition has been corrected the circuit breaker will reset and the booster will resume normal operation. The second level of protection is a fuseable link (fail safe), if the electronic fuse should fail to trip (extremely unlikely) the fuseable link will rupture and protect the vehicles electrics.

How much will the booster increase my alternators output voltage by?

The booster will increase your alternators output voltage by around .5V - .6V on average.

I have read that only a DCDC charger will fully charge my battery, is this true?

This is a popular misconception, your alternator charges at around 14.4V@24C (normal alternator) and around 14.2V - 14.4V@24C for a high temperature compensated type alternator with a HKB Electronics booster diode fitted. A DCDC charger charges at around 14.4V@24C ie the same as your alternator!

As you should be able to see from the above, if a DCDC charger can fully charge a battery then a alternator can too.

Which will charge my battery faster, an alternator or a DCDC charger?

A DCDC charger needs to protect its self from over loading, to do this it has to limit its output current  to a maximum safe value, in the case of a 20A charger it will be 20A, a 40A charger 40A etc. To achieve this it will start charging at a low voltage, ie in the case of a severely depleted battery it might be only 10.5V for instance, then gradually increase its output voltage to maintain a constant 20A charge into the battery until it gets to its maximum output voltage, ie 14.4V@24C in the case of the CTEK. It will then swap to constant voltage charging, this won't occur until the battery has reached an approximate state of charge (SOC) of around 80%, it will then continue to charge at 14.4V until the battery charging current drops to around 2A at which time it will enter its trickle charge float mode.

An alternator on the other hand does not need to limit its output as it has a much greater output capacity, a reserve capacity of around 60-100 amps is typical. It will reach its maximum output voltage within a few seconds of the vehicles motor starting as it is not current limited, allowing the battery to take whatever charge it will accept.

For instance, in an under bonnet setup with a have a 120Ah alternator, a 66Ah Optima battery as the aux and simply VSR we can charge the Optima from 0% SOC to 90% SOC in around 50 minutes.

A 20A DCDC charger will take around 4 hours to reach the same level, assuming you have nothing else connected to the charger, if you are also running a fridge or two of it then recharge time will increase.

What about if the battery is mounted in the rear of the vehicle or a camper trailer for instance? It will certainly take the alternator VSR setup longer to charge the battery than it would in an under bonnet scenario, but providing adequate cabling is installed one would expect it to still take considerable less than the 4 hours the DCDC charger would take.

The following details the performance of a typical in car setup:

Test environment:

Toyota 120 Prado D4D

Cranking battery Optima D27F (fully charged)

Aux Marine Pro 600 about 50% SOC (12.04V)

Rotronics isolator in simple VSR mode

Alternator output voltage about 14.3V – 14.1V

Ambient temperature 25C

Monitoring equipment, wireless amp & volt meters.

Sample Rate Amps & Volts = 2 Seconds interval, range auto.

The following graph is constructed from the real time data:

A couple of points to note, the vehicle was fitted with 10mm2, and fuseable links, the fuseable links introduce an additional .15V drop under high charging currents. Using 13mm
2 cabling would have result in an even quicker recharge times.

Peak current 61.6A

Average recharge current first hour 28.1A

Average recharge current for last 40 minutes 14.68A


Total charge put back in in a 1 hour and 40 minute, was 42.78Ah (85.5%)

A 20A DCDC charger would have replaced 33.33Ah in the same time.(66.66%)

The total recharge time would be about the same as a 20A charger, however the simple VSR will replace the bulk of the charge much more quicker, the more deeply discharged the battery is, or the more battery capacity you have the more the balance swings in favor of simple the VSR Setup. If  13mm2 had been used for the installation the overall recharge time would have been much shorter than the DCDC charger could manage. Also keep in mind, with a simple VSR setup, adding another one or two batteries will have little effect on the recharge time, assuming each battery is individually wired to the VSR and the alternator has sufficient reserve capacity to charge all the batteries. Adding an additional battery to a DCDC charger will double the recharge time, adding a third will triple it etc.

I have been told that raising the alternator voltage will cook my batteries, is this true?

Simple answer is no, in recent years manufactures have lowered the charging voltage for two main reasons:

1/ Lowering the charge voltage reduces the load on the engine at idle and improves the standard fuel consumption figures manufactures use to sell cars, lower fuel consumption figures sells cars.

2/ Lowering the load on the engine at idle is a cheap way to reduce exhaust emissions and helps the manufacture meet strict overseas emission requirements.

Unfortunately lowering the charging voltage is not good for the cars battery and has led to a rising trend in premature battery failures. The Alternator Voltage Booster simply restores the alternators charge voltage to pre low output alternators charging voltages.

Note, not all manufactures have introduced low output alternators as they didn't need to to meet emission requirements. Some manufactures have introduced ECU control alternators whereby they can turn the alternator off to lower engine loads even further, some of these types of systems allow the "smart charge function to be turned off" by doing this the manufactures can meet the emission requirements but then turn the "smart charge function off" when it causes issues to the customer.

Recently at least one manufacture that has been using low output alternators has recently raised the charging voltage of their latest models due to charging issues.

How to wire parallel batteries and why?

How to wire parallel batteries and why can be found here.