Battery Combiners vs Isolators

[Bill Murray]

My 1999 H410 has an electrical system composed of a house bank of 2 4D batteries and 1 SRM-24 starter battery, Freedom 20 Combi inverter/charger and a 80 amp alternator.Hunter chose to wire these with a battery ISOLATOR and a solonoid (relay) which connects both battery banks when the starter circuit is activated. (There is seemingly no way to manually "parallel" the battery banks other than this solenoid.) The batteries seem to me to be continually undercharged ( 12.6 volts typical floating voltage).

I have two issues/questions -

1. I think using an isolator could be improved by changing to a battery COMBINER to avoid the voltage loss inherent in using an isolator. Has anyone made this modification to a similar sytstem (with the Freedom combi) and what experiences / issues did you encounter? ( I know the archives contain my posts on how to do this to a H29.5)

2. It seems to me that the solenoid is lacking in some possible respects - 1st it might not work in low voltage situations - exactly when you want it to work! and 2nd some people say you want to actaully isolate your house batteries (and any sensitive electronics) from the starting process as much as possible. In fact some battery combiners have a circuit which disconnects the combiner during starting for just this reason.

All thoughtful comments would be welcomed.....

 

[Don S/V ILLusion]

both are improvements

Bill
There are a few permutations to what you plan which may be preferable. Although replacing the isolator with a combiner will be in improvement, that setup still leaves you with a charging system which cannot differentiate between the house bank and start battery which in turn can cause premature start battery failure due to over-charging. Conventional wisdom is to trash the isolator in preference for an eco-charger to the start battery. Doing so will obviate the need for the separate relay. Alternatively, you can do as you describe but if I were going to the trouble of making this change, I'd opt to optomize the result. As to your low voltage oncern, the combiner is intended and designed to perform at that event.

Regarding your second point about voltage spikes and sensitive electronics, most marine electronics isn't that sensitive and will survive a typical voltage spike during engine start. If that were not true, most of us would be replacing them constantly. If you do have something which is that sensitive, any 12V UPS will solve that issue independent of the boat's systems.

 

[Don12364]

Isolator?

Bill,
Presumably by 'isolator' you mean one of those devices with diodes inside which drop 0.7 volt when the battery is on charge. Unless you have remote sensing on your charging circuits this setup will guarantee under charging for both engine and house batteries. Presumably also you have two "Battery Isolator" switches, one for each battery.
My H376 came wired with two battery isolators and a combiner but has no need for an isolator. Yours may have been added when the Freedom Combi was installed and it is not really necessary. My alternator is connected to the engine start battery but, as you say, the combiner comes in as soon as the key is turned so both batteries get charged simultanoeusly. I see no reason why the engine battery should get over charged because it will hardly draw any current whilst the house bank is being charged. As evidence my engine battery is still good after 11 years from new but I have changed my house bank once and am about to change them again.

There is a problem with this set up when charging from shore power. My Freedom 10 Combi does not have a separate output for engine battery charging so I simply took a 12v DC power charger from an old power tool and connected it across the combiner coil and fed it's mains side from the shore power inlet. Now, as soon as I plug in to shore power, the combiner comes in and both house and engine batteries get charged in parallel - and to the full extent as dictated by the charger.
It was necessary to insert a small 5 amp diode in series with the +ve wire of the combiner coil input from the engine so that the power brick didn't power up the engine circuits when on shore power. This system has served me very well for the last 10 years and, IMHO, is better than any I have seen elsewhere including voltage sensitive relays.