Charging two types of battery at once

[Robbo22]

Lord knows theres enough been written here regarding Battery charging yet despite a short search I havent been able to a find a direct reference to my question.


It is this.....as I understand it when I've installed my new (1, 2, Both) Blue Sea (9000e series) selector switch and set it to "Both" then both batteries will charge as I run the engine/alternator. I was planning to use a starting battery for engine starts and a Deep Cycle for electric trolling motor, lights, and fishfinder etc

Can anyone tell me if its OK to have a Marine Starting battery charging along with a Deep Cycle at the same time by the same alternator. Or, should both batteries be of the same variety.

I ask this as we use different types of chargers for Deep cycle and our regular auto starting batteries?

 

[jtexas]

Re: Charging two types of battery at once

What engine? It's a rare alternator that can keep a trolling motor battery charged. More likely you'll end up with two dead batteries. Unless you plan on anchoring up in party cove for hours with a hi-power CD amplifier blasting tunes, or running a fancy oxygenated bait tank full time, hook the accessories to the cranking battery, and charge the trolling batt when you get home.

I been using interstate deepcycles for cranking for a long time with good results.

 

[Robbo22]

Re: Charging two types of battery at once

Engine is a 1984 Volvo Penta AQ 125 A...

Cant an alternator charge two batteries at the same time.....apologies but when it comes to electrics I'm somewhat of a Techno-Peasant

He he, also.....no its not a party boat with 18" Yorkville bass bins, dont want that nonsense within 5 miles of me when I'm fishing.

 

[tommays]

Re: Charging two types of battery at once

It is not IF they can be charged BUT how long it would take

They make units for charging off the ALTERNATOR that will sense that the main battery is fully charged and switch to the other battery


I am in a mooring field full of 800 boats without shore power and people do manage to keep there battery's charged

 

[jtexas]

Re: Charging two types of battery at once

We didn't know whether you had a small outboard with a 4-amp alternator or twin diesels - sure it can charge 2 batteries, it's just that trolling motors are so power-hungry, it might take hours of running WOT to replace the power it uses. That all depends on your equipment and useage patterns, etc., actual mileage may vary.

 

[Robbo22]

Re: Charging two types of battery at once

We didn't know whether you had a small outboard with a 4-amp alternator or twin diesels - sure it can charge 2 batteries, it's just that trolling motors are so power-hungry, it might take hours of running WOT to replace the power it uses. That all depends on your equipment and useage patterns, etc., actual mileage may vary.

Jtexas.....My thanks for your replies.....

OK, we've established that you can charge two batteries at the same time from the same alternator (albeit slowly) so then, to re-iterate my original question, is it safe to charge a deep cycle AND a regular marine start battery simultaneously from the same alternator......... I pose the question as two different types of charger are usually recommended for Deep C and regular start batteries. I mean, will linking the two types in this way somehow internally damage one or both batteries ?.....

Maybe I didnt frame my question adequately but that was the intended thrust of my original post ?

Regards
Rob

 

[Seon]

Re: Charging two types of battery at once

You'll need to install an "Multi Battery Isolator" available at most auto parts store.
Once connected, you'll be able to charge two batteries as you described. Here's a link that'll give you more info: http://www.mastertech-inc.com/vanner/iso.html

 

[Silvertip]

Re: Charging two types of battery at once

You are a prime candidate for an ACR (Automatic Charge Relay) rather than a battery switch. This is essentially an isolator that allows the main start battery to be charged normally. When it is topped off the ACR switches to the secondary battery and charges it. When parked, all accessories would run from (or should run from) the secondary (deep cycle) battery. The start battery would be isolated and therefore protected from accidental discharge. Keep in mind that start and deep cycle batteries have different charging profiles. If you essentially parallel them, the voltage regulator can only monitor "system" voltage and reacts accordingly, treating your deep cycle battery like a start battery. Will it charge both? YES. Will it kill the deep cycle? Don't Know! Is it the best system? In my view no! In your situation the ACR is my recommendation. If you have dual start batteries, then a battery switch makes sense.

 

[Robbo22]

Re: Charging two types of battery at once

You are a prime candidate for an ACR (Automatic Charge Relay) rather than a battery switch. This is essentially an isolator that allows the main start battery to be charged normally. When it is topped off the ACR switches to the secondary battery and charges it. When parked, all accessories would run from (or should run from) the secondary (deep cycle) battery. The start battery would be isolated and therefore protected from accidental discharge. Keep in mind that start and deep cycle batteries have different charging profiles. If you essentially parallel them, the voltage regulator can only monitor "system" voltage and reacts accordingly, treating your deep cycle battery like a start battery. Will it charge both? YES. Will it kill the deep cycle? Don't Know! Is it the best system? In my view no! In your situation the ACR is my recommendation. If you have dual start batteries, then a battery switch makes sense.

Bingo !...this is exactly the info I was looking for......Thanks Silvertip, and others who took the time to reply.

Rob

 

[Boatist]

Re: Charging two types of battery at once

First step is to know how big your alternator is. If it is 30 amps or more then You can charge both batteries thru your switch in the both postition or you can charge thru a battery isolator or you can charge with a ACR (automatic charge relay). It really makes no difference.

Most I/O alternators are a least 30 amps and many newer one can be over 100 amps. The alternator supplies a DC Voltage to charge the batteries. Most are between 13.8 and 15.0 volts. 14.4 volts common.

So if you charge thru your switch in the both position when you set it to both before starting the discharged trolling motor battery will be drawing current from your charged starting battery. If the starting battery is weak and the trolling motor discharged this could leave you dead in the water. After the motor starts then both batteries will get 14.4 volts. Since the alternator is big enough to supply more current than either battery will take at 14.4 volts they will both charge at that voltage. Actually for the first 30 second after a long hard start and with a discharged trolling motor battery it may not reach 14.4 volts but soon after it will. So both batteries will charge up.

Charging batteries with a ACR switch. Again when you start the alternator will start puting out current trying to reach the voltage of the regulator 14.4 volts. The starting battery will get full voltage and the trolling motor will get nothing until the starting batrery reaches a certain voltage. This ensures your starting battery gets charged up to a point before start charging the trolling motor battery. This is a very good thing if you have a small alternator like on small or older Outboards. It may only be 8 amps. So when you start and have the blower on and the navigation light, a radio and depthfinder the battery may only get 1 or 2 amps and it can take a while to replace the starting current. When it does charge up to the Voltage that the ACR is set to the relay will pick and voltage is also applied to the trolling motor battery. Many think both battery charge from that point on but it does not. What happens is when the ACR picks and the Voltage is also applied to the trolling motor battery since the alternator is only supplying 1 or 2 amps not used by the boat the trolling battery draws more than 2 amp and the starting battery voltage drops. The ACR see the voltage drop and drops the charging realy. Then the starting battery again reaches the voltage where the ACR picks.
The result is the ACR sound like a busser and chatters. Now with a 30 amp or more alternator this will still happen but will not go on for two long, as the trolling motor will start to gain some charge and not load the starting battery as much.

Charging both batteries with a battery isolator. When you start your motor both batteries will start to charge at the same time. The battery with the lowest voltage will get most of the charge. In the case of a charged main battery and a dead trolling motor battery the trolling motor battery will get most of the charge. As soon as the trolling motor battery gets above 13.3 volts then the starting battery will also get charged. The diodes in the isolator will drop about .7 volts, so if the voltage regulator is set to 14.4 Volts each battery will charge at 13.7 volts and take longer to reach full charge. If your alternator has an external regulator then the input to the regulator should come from the starting battery and this will again raise the voltage for both batteries to 14.4 volts or what ever voltage the regulator is set for.

Hope this helps some. Again the best set up really depends on the size of your alternator.
Small alternator 8 to 10 amps probably best to not try and charge the trolling motor battery.
Large alternator with an external regulator then I like the battery isolator best.
Large alternator with an internal regulator then ACR is a good choice.