Back ground notes.

1982 the start of the Powercentre story

Relay split charging ?

Power-lockout ?

Reserve power ?

Link start ?

Starter drop-out ?

Programmed charging ?

Bi-directional charging

Maintenance charger ?

24 volt split bank charging ?

FAQ.

What is feed back ?

Bouncing contacts ?

Can relay switching damage the alternator

Why not use blocking diodes ?

Why not use MOSFET switching ?

Why us a relay for split charging ?

Various charging circuits can be produced from the P2 series split charge modules, this allows a system to be tailored to suit a particular boats requirements. Rather than trying to tailor a boat to suit a standard charging unit.

Single engine light duty 40 amp

Single engine system 100, 200 amp includes power-lockout

1, 2 or both switches 40 amp and 100 or 200 amp, includes power-lockout option

Bow battery

Twin engine light duty 40 amp

Twin engine 100, 200 amp

2 bank with power-lockout

3 bank with dedicated service battery

3 banks, includes bow battery

4 battery banks

Power reserve typical layout

Power-lockout typical layout

Reserve power

Maintaining a power reserve from a battery supply has been tackled from a number of areas. You can isolate part of the load via a power-lockout system, you can switch to a second battery bank. Both have there problems, with power-lockout you loss the use of equipment, when switching banks you get spikes, or even power loss. Our approach has been to treat the battery as one bank, but the critical equipment is supplied from one section, the non critical equipment from another. The two section being linked via a power relay, thus if a low battery is detached, the relay opens to isolate the two banks. This has the effect of minimising any spikes, and maintained power continuity for all equipment. Critical equipment being supplied from it’s own reserve bank, while full equipment usage is maintained from the remaining service bank for a limited period. Battery bank continuity is automatically restored once a satisfactory service battery voltage is restored.

A second use for the reserve power system is that on engine starting, normal or link start, the relay can automatically drop out, isolating the critical equipment from starter motor low voltages and spikes.

Integral remote battery isolator relay / reserve power relays in a single package allows a remote, or high level reserve battery bank to be installed, with localised drop-out and isolator relay package. Providing added protection from flooding to low level battery installations.

Power-lockout

Dates back to 1982, with the introduction of the P3000 system this allowed high load equipment to be automatically isolated at a low service battery voltage. Power was automatically restored when the service battery returned to a satisfactory voltage. Thus providing a dual function, stopping a constant load such as a fridge from totally flattening a battery, thus loosing power for navigation equipment. Or providing a buffer to maintain a minimum battery level for improved battery life

The new  standalone unit will feature dual relays that have a split drop-out settings. By having two voltage settings, it allows load shedding in stages, providing better power and battery management. There is a built in time delay ( factory adjustable ) to allow for sort high current draw. The voltage trip levels are all user adjustable to allow fine tuning. As with all the systems once battery capacity is restored circuits will be automatically re-connected. A manual timed override system is included to provide a power supply to equipment on a temporary basis, and a emergency override can be installed if required.

The other feature of the new system will be the re-introduction of the battery status display, allowing monitoring of voltage around trip point, and recharge point.

1973

the common way to charge a second battery was blocking diodes. Then as to-day the diode volt drop problem was the main stumbling block. It was against this background that we developed, and patented a new system, this was marketed by Astrali as the Apollo energy pack. Following  on we set out to develop the next generation, and 1977 saw the first Kdd product. The Maxcharge 5.10, providing charge from both car and mains. With the improvement in alternators, and there extended fitment to marine engines over the next few years, we set out to build the next generation split charge system.

1982

saw the Powercentre P4000. production release, this offered the following standard features:-

split charge relay system, for two battery banks, that required no mod’s to the engine charging system. This utilised a programmed charge relay driven by the display, giving initial charging to the engine battery and zero volt drop.

battery condition display  provided by LED’s giving status for each battery banks, and recharge level,

bi-direction charge, allowed the service bank to charge the engine bank from a second charge source, such as a single output mains charger or solar panel.

power-lockout at low service battery voltage the relay will isolate non critical loads to stop the service battery being drained to a very low level. Power is restored at a satisfactory battery level.

1984 saw the release of the P5000, 2 engines and 3 battery banks units appeared in 1984. These units had the same functions as there predecessors, but also interfaced with the multi stage mains battery charger we produced. Providing a programmed charge system for off-peak charging of the engine batteries.

Over the next 10 years, many 1,000’s were made as an integral part of Powercentre switch panels supplied to production boat builders.

Starter drop-out

Is used when a second charge source, such as a solar panel or wind generator, is fitted to the service battery. This means that the charge relay can be engaged, when the engine battery is on charge. Should the engine be started now, the current would be drawn from both engine and service bank initially, causing possible overload to the charge cables, and spikes to electronic equipment. The drop-out interface links the control module to the starter solenoid, so that on turning the key  the charge relay is dropped out before any load is applied.

Link start

This allows the charge relay to be used to link the engine and second battery for starting if the engine battery is low. It’s operation depends on the engine installation, and battery charging system installed.

Single engine boat can have a problem from low voltage, or spikes to electronics if used for engine starting. Installing reserve power can solve this by isolating the electronics on start up via the starter drop-out system, in this case it would be the reserve relay. Battery bank size is also a consideration in this case, the non critical section needs to be large enough to cope with the starter load with normal power levels.

Twin engine installations can be approached in a number of different ways:-

• Were one battery bank supplies domestic power, you can use a similar set-up as for a single engine.
• Were the system is also supplying a battery in the bow, either inter-link the reserve power system, or if not fitted a dual supply module can be installed. This will allow power to be supplied from the engine running for electronics, thus avoiding low voltage and spikes.
• Fit each engine with a dedicated starter battery, the services are then supplied from a third battery bank.Thus there is always a clean supply during engine start, the link relay connects the engines directly, and no power is drawn from the service battery, thus maintaining a clean supply.

Relay split charging

The system we use goes back to the late 1970 , early 1980’s which we developed for the Powercentre range. How does it work ?

i) a battery has three defined voltage ranges, on load ( 12.4 - 10 5 v ), no load ( 12.7 - 11.85 v ), on charge  ( 13.2 - 15.6 v ), note, voltages are a guide and the actual value vary with many factors.

ii) the voltage you see at the battery is produced by the battery internal resistance, not the alternator producing a voltage, it produces watts, which is why the amps fall as the voltage increases, though this is also effected by battery resistance in the later stages.

iii) the alternator starts charging the engine battery, normally this will rise rapidly, unless a low battery or starting problems are encountered. Either way once the threshold voltage is reached, the relay is engaged and the batteries are connected in parallel.

Iv) with the connection of the service battery, two things happen, first there is a small discharge from the engine battery, the voltage drops, and the alternator output takes the least line of resistance, and flows to the service battery.

v) normally if the service battery is not very low, the short discharge from the engine battery, and the alternators total output pull the service battery voltage rapidly above the drop-out threshold voltage, and the relay locks in.

vi) due to the voltage falling, lower resistance in the service battery, it is to low to charge the engine battery so all alternator output goes to the service bank.

vii) once the voltage rises to the charge level of the engine battery, it will start to take a charge and all batteries will take a charge that suits them.

viii) if charge stops, the voltage will fall, rapidly if the service bank is supplying a load, and drop into the lower voltage range. On passing the drop-out threshold voltage, the relay will drop out, isolating the engine battery from the service load.

Programmed charging

Is basically an extension to the Powercentre system, using stepped switching voltages, and the physics of the battery to control charge flow and location. Where you have multiple battery banks, the system allows each bank to be charge separately initially, then as a large bank to finish charge.

How doe it work.

Let us take a twin engined boat, with domestic power supplied from the starboard engine bank, and a bow battery for bow thruster and winch.

I) the port engine will initially charge it’s battery, rapidly reaching threshold and putting the bow battery on charge, voltage drops and full output goes to the bow battery

Ii) the starboard engine will be charging it’s battery, which may be low due to sitting at anchor, and also supplying domestic power, fridges, navigation equipment etc. This can generate two problems, the domestic load is using alternator output current, reducing amperage to the battery charging. But can also can reduce output voltage due to the type of load, again reducing battery charging.

Iii) but once the port engine has put a charge into the bow battery, it has surplus capacity that is doing nothing, so the link start relay is energised, and the batteries connected into one large bank.

Iv) we now have two alternators charging one bank, the port engine and bow batteries probably at a higher charge level, so the voltage falls to the voltage generated by the domestic load and starboard battery. Both alternators will charge this bank until it reaches the charge level of the other two, all batteries will then be charged  as one.

V) when the voltage rises to a level equal to the setting of the lower alternator regulator, the alternator will shut down, leaving the higher setting one to top up charge.

With single engined boats, it allows batteries to be charged in a set priority based on importance, rather than which is lower.

Bi-direction

All the units ( from 1982 ) monitor the voltage of both battery banks, this allows the relay to charge from either battery. Thus the engine will charge a service battery, and the service battery will charge the engine battery via a solar panel, wind generator, or single output battery charger.

Allows the engine battery to be charged and also act as a dump for surplus power from solar panel or wind generator.

Provides alternator redundancy for twin engine installations, allows one alternator to charge all battery banks should one alternator fail.

Maintenance charger

Not new, we first introduced them back in the mid 1990’s, as part of the cycle of the mains battery charger we made, or as a stand alone unit. It was intended to provide a charge cycle to batteries when a boat was not in use, only powering up when a charge was required, thus minimising current consumption.

In operation the system will power up, and provide a charge cycle to 14.5 volt, at this point it will turn of the mains, and introduce a counter current to the battery, the charge cycle will the be repeated. The length of pulse, and the time interval between pulses varies with the recharge level of the battery.

This has the effect of breaking down and minimising sulphation, provide a deep charge to the plates, assisted by the counter current, and maintains a mixing effect to the electrolyte during the charge pulse, which can be a problem when maintaining batteries at float voltage for long periods.

24 volt split bank charging

An interesting concept, you take a 24 volt battery bank, and charge each half independently.

This allows both half's of the battery bank to take a independent  optimum charge, either bank can be at a different voltage, take different charge current, in fact they may even not be on charge at the same time.

This means that all the batteries are charged separately, you do not over charge, or under charge a battery or bank. Thus the batteries take an optimum charge, maximise battery capacity and life.

What is charge feedback , and is it a problem ?

No it’s not a problem, we identified it back in 1980 and fitted the low volt drop out circuit, and correct spec contacts to avoid any possible problem.  In fact we use a little feed back to help soften the load on the alternator when the relay connects the service bank.

For it to be a problem you need an under sized relay controlled by the alternator warning light. It is then assumed that a full engine battery will discharge into a dead flat service battery. What happens is that in this situation the voltage will drop rapidly, the low volt sensing circuit will then drop out the relay to prevent the discharge.

Are bouncing contacts a problem with charge relays ?

Not something we have come across in 25 years. The force to overcome the solenoid clamping load on the contacts is likely to result in structural failure in the boat before the contacts are opened. Also the contacts are arrange so that there faces are vertical when installed, thus any vertical shock load will only try to slide the contacts faces, not open them.

We have come across chattering contacts with badly designed systems, where the hysteresis is to low or non-existent. Thus when the relay cuts in, voltage drops, and the relay drops out, voltage shoots up, relay cuts, and on and on.

Can relay switching damage the alternator ?

No the alternator is always connected to the engine battery, the service battery is connected in parallel with the engine battery when the contacts close. The current then takes the least line of resistance, which is normally the service battery, which then takes full alternator output till it catches up with the engine battery. All the batteries then share the alternator output based  on there requirements.

Why not blocking diodes

A number of reasons that we do not like them for charging,

Volt drop 0.5 - 1.0 volt, can reduce recharge levels to 50%, we are not against them, we do use Schottky diodes for power supplies, it’s just the application we are against.

But they are simple ?, yes but to make then work you have install smart regulators, making it even more complicated and expensive. You also have to change the engine wiring to run the alternator output through them, so a diode failure can result in lose of charge to a battery, or a shorting link between batteries. Every additional connection point is also a potential weak link due to corrosion.

They are also not flexible, you cannot use them for integral link start, or bi-directional charging.

MOSFET switching

We looked into MOSFET switching as a cheaper alternative to power relays in the mid 1990’s, at the time we turned them down on a number of points, they were liable to thermal run-away, they included a fly-wheel diode that allowed a reverse feed , thus batteries would back feed the alternator output terminal. They were also not flexible in use, as per blocking diodes, you could not provide link start or bi-directional charging. Plus you needed to alter the engine wiring and to run the charge through them, thus a fault could loose charge to the engine battery.

Why use a relay

Back in the late 1970’s when we started the design of the Powercentre system we set a specification.

I) That the alternator should always be permanently connected to the engine battery, this was to maintain s secure charge to the engine starting battery, minimise the number of connections, and avoid any modifications to the engine wiring.

Ii) to be able to automatically control when the switching should take place.

Iii) minimise volt drop in the system

V) allow maximum flexibility with minimum components, for example one relay will allow split charging from the engine, charge from a second source , or allow the engine to start from the second battery bank.

Vi) to allow installation with the minimum number of connections, or additional wires.