Battery Isolator Amps query

[bony]

Hi folks,

Does the amperage rating of a Marine battery Isolator in a Dual sytem refer to the output of the alternator or the amperage of the batteries.

Here is an example of one I am looking at -

ProSplit D - 70 Amp 2 Output Marine Battery Isolator - Low Volt Drop Split Charge | MonsterMarketplace.com

My alternator puts out 65 - 70 amps and I am assuming I will need an isolator with a rating of 70 amps to handle this. Is this correct or is it normal practice to use an Isolator with a highrer rating , say at 90 amps?

Thanks,
bony

[djmarchand]

The isolator needs to be rated to handle the current from the alternator. A 70 amp isolater should be fine with a 70 amp alternator as you will rarely if ever see 70 amps from that alternator in real life.

David

[bony]

Hi David,

I've been reading up a fair bit on the subject but just needed to get some clarification on that point. Thanks for the advice.

Cheers,
bony.

[Andina Marie]

Diode isolators have a built in voltage drop which can reduce the voltage delivered to the batteries and cause heat. You could consider a Combiner100 for about the same price that is rated for alternators up to 100 amps, has no voltage drop and can handle voltage spikes up to 1000 volts which would destroy a diode isolator in 1/1000 th second. They come with unlimited warranty that you will not get on a diode isolator.

[donradcliffe]

You should get clarification on whether the rating is for the alternator side or the maximum current that can go to each output. I had one melt down when one of my battery banks had a shorted cell and all the power went to one leg. I bought the next size up when I replaced it--the cost wasn't that much different as long as it wasn't sold as a 'marine' unit.

[bony]

Hi Andina Marie,
Thanks for that advice. I've had a look around for the Combiner and
am wondering if the 100 amp unit found on the link below would be suitable, it is on special at a good price?

Combiner 100 Sheet

It states that it is rated at

• 75 amps continuous rating, 400 amps closing current (2 seconds), 100 amps for 5 minutes
• Suitable for alternators up to 100 amps, up to 18 volts.

The website also has a lot of good information regarding Battery Combiners.



And thanks also to donradcliffe,

It seems the word "Marine" has the same crazy effect on retailers worldwide in which they feel it necessary to triple the price of their goods.

I will take heed of your good advice.

bony.

[Andina Marie]

The experience quoted by donradcliffe points out the big difference between diode isolators and Combiners. An isolator charges the LOWEST battery first, then when its voltage reaches the voltage of the second battery BOTH are being charged. This puts maximum stress on the alternator and the isolator.

A Combiner100 does not start to charge the house battery (typically the LOW one) until the starting battery gets up to 13 volts or more. As the current supplied by the alternator drops off due to the charge received by the starting battery, the unused capacity of the alternator is diverted to the house battery. The amount of charge delivered is controlled by cycling on and off until both batteries are above 13 volts and can safely be charged in parallel.

[colemj]

Originally Posted by Andina Marie

The experience quoted by donradcliffe points out the big difference between diode isolators and Combiners. An isolator charges the LOWEST battery first, then when its voltage reaches the voltage of the second battery BOTH are being charged. This puts maximum stress on the alternator and the isolator.

A Combiner100 does not start to charge the house battery (typically the LOW one) until the starting battery gets up to 13 volts or more. As the current supplied by the alternator drops off due to the charge received by the starting battery, the unused capacity of the alternator is diverted to the house battery. The amount of charge delivered is controlled by cycling on and off until both batteries are above 13 volts and can safely be charged in parallel.

Isn't a combiner usually installed so that the charging source goes to the house bank and the combiner combines in the starter battery when the house voltage gets above the setpoint?

At least that is how the combiners are set up in our boat, and how the instructions recommend installing them.

Mark

[Andina Marie]

In the early years before we had accumulated field experience it was recommended to connect the alternator to the house bank and let the Combiner100 charge the starting battery. After a few years it was evident that the relay contacts were going to last longer than any boat they were in and there was no need to change the alternator/engine wiring.

By leaving the alternator on the starting bank you give desirable PRIORITY to the starting battery and use the regulating feature of the Combiner100 to limit the load on the alternator to a safe level for very large house banks with low charge.

It makes installation much simpler, just 2 battery cables and a ground.
It saves risking warranty on new engines due to changing wiring.

Our Combiners are standard equipment on some emergency vehicles where our Combiner160 is operating with a 200+ amp alternator. The overload was causing thermal protection shut down and heavily loaded house batteries were not getting enough charge. Connecting the alternator to the house bank on those vehicles solved the problem but otherwise is not needed although it does no harm.

[colemj]

I'm still confused. In most boats, the alternator is already wired directly to the house banks. Our boat was wired that way from the factory. A wire leads from the house battery to the combiner to the start battery. In other words, just two battery cables and a ground.

The start battery is always almost fully charged - all it does is work for a few seconds to start the engine, so I don't see the need to have it as the priority charge.

I don't understand how a combiner regulates the charge to the house bank since it is only a relay that, once closed, combines all batteries into one large bank and the charging source then sees the low voltage bank. If anything, I would think that suddenly combining a charged starting battery to a low voltage large house bank would cause some serious discharge current flow from one to the other - which would not be as bad if the house was connected once charged a bit.

I wouldn't even want a regulation feature in a combiner because that is why we have programmable alternator regulators with temperature sensors. A standard internally regulated small case alternator would never be under a harmful load in any case unless the alternator and battery bank sizes were severely mismatched beyond normal expectations.

Don't get me wrong - I think your combiners are excellent products and were in use on our boat for 14 years before a recent lightning strike took them out. I am just seeking education because I am not understanding how combining battery banks makes any difference to the load on the alternator, how the wiring is any different regarding which bank the alternator is connected to, and why it is desirable to give the start battery priority on a cruising boat.

Mark

[Andina Marie]

All engines come from the engine manufacturer with the alternator connected directly to the starting battery, typically via the starter cable. The boat manufacturer can then connect however they like. The most common boat setup (especially for small boats) is just a starting battery. If a little more fancy the engine is connected to an off,1,both2 switch so either battery would be charged directly. Under most circumstances it makes little difference. Our Combiners are standard equipment some boats but usually an owner add-on.

Our Combiners regulate the load on the alternator by using differential voltage detection and timing circuits. They are designed to roughly deliver 1 amp-hour of charge on each relay closing until the second battery voltage gets over 13 volts. It is heat that kills overloaded alternators, not the actual current flowing. By cycling once or twice a minute "packets" of charge are delivered and the rate of delivery depends on battery voltages and alternator capacity.

Do not confuse it with a VOLTAGE regulator, voltage regulation is left entirely up to the charging source. It is a CURRENT regulator. Devices like the echo charge are secondary voltage regulators and unlike a Combiner, they attempt to emulate a charger output.

Thanks for the vote of confidence . Your lightning damaged combiners are covered by our UNCONDITIONAL warranty and will be replaced free of charge if you still have them.

You can set your own priority by how the Combiner is connected. My personal preference as a live-aboard for 14 years is that being able to start an engine is more important than TV.

The comparison was being made to diode isolators. A diode isolator charges the lowest battery first and adds the other battery(ies) while the lowest is still at peak bulk load. If the alternator on the engine was designed for handling monster house banks then no problem but frequently stock alternators were part of an automobile or truck package and intended for a much smaller battery bank and can suffer from overheating on large battery banks.

[colemj]

Originally Posted by Andina Marie

Thanks for the vote of confidence . Your lightning damaged combiners are covered by our UNCONDITIONAL warranty and will be replaced free of charge if you still have them.

Thanks for the explanation. I know the combiners are still covered under warranty, but we are in Panama and shipping/customs/etc would be more than they cost. Besides, I have already repurposed the 70A relay and the utility box of one of them in two other projects (these were the old 70A combiners in grey boxes).

Mark