Using batteries with different amperages under the same battery charger

[Eren]

I have a problem with my bow thruster. With very short usage, it switches itself to safe mode and comes back again in about half an hour. I first suspected from overheating but in the end it came out to be a foulty battery at the dedicated thruster battery bank. The thruster batteries at the current setup are gel type, which are not found to be suitable. Now the electrician advices me to use Optima batteries, which are AGM type and have very high "sudden load" capacity. I am convinced with this choice but I have 2 issues that I am not so sure. First of all the other batteries under the same battery charger are gel type and secondly they are 100 amps. The highest capacity Optimas are 75 amps. So I wonder if these inconsistencies can be problem.

I will be glad for your help.

 

[Portofino]

Does the charger have seperate outlets say 3 allowing them each to be set up to what ever bat type ?
If not then buy a dedicated seperate charger for the BT bats .
Where are these BT bats .?
What charger ( s) have you got doing what ?

 

[Eren]

Does the charger have seperate outlets say 3 allowing them each to be set up to what ever bat type ?
If not then buy a dedicated seperate charger for the BT bats .
Where are these BT bats .?
What charger ( s) have you got doing what ?

I have 3 chargers, 2 x 24V and 1 x 12 V. I will soon find out which one is doing what. But I am sure that there is no dedicated charger for the thruster batteries, they are sharing a charger with some other batteries. The batteries are located at the bow, right next to the thruster. I don't want to go to a solution for a dedicated charger, just want to know if using batteries with different amperages under one battery charger will give harm to something on the system.

 

[[2068]]

I was advised to go for a lead-acid “starter” type battery for the bow thruster, as it will pull something line 300-400 amps when in use. It is working well so far, but my other batteries are also lead acid.

Having batteries of different capacities on the same charger should not be a problem ... they will be at different states of discharge anyway.
Mixing different types on the same charging circuit is not a good idea.

.

 

[Portofino]

just want to know if using batteries with different amperages under one battery charger will give harm to something on the system.

And wether different types e.g. AGM and gel or lead acid are ok together in the same charge circuit ?

Would have thought bats need to be SAME amperage in a circuit , otherwise the lower ones may overcharge ? - thinking safety here or the bigger ones not reach max charge ( cos it's turned it down sensing the smaller is charged ?)

Also I know the charge regime bulk / float / rest / desulphor - etc is different between types - not a lot but enough to set today's all" singing n dancing " chargers up to match the bat types .
Thinking more in terms of longevity here

 

[jrudge]

Given the legendary battery thread and the importance of how the batteries are wired if the battery at the bow on very long leads is not on a Sep charger or circuit I doubt it will ever achieve full charge. Buy a cheap separate charger

Also they have settings for different types so I cannot see you can mix types.

 

[MapisM]

Would have thought bats need to be SAME amperage in a circuit

Yup, that has always been my understanding too.
Not only that, but as I recall from what Annageek explained us, even one slightly misaligned battery within the same bank can lead to troubles.

That said, the DP recharging system is against these principles: while the battery charger does have two 24V channels, one for service bank and the other for engine bank, as soon as the engines are turned on the following happens automatically:
- battery charger is disconnected
- both banks are kept connected in parallel
- both alternators (also in parallel) keep both banks recharged while under way

So, it's pretty obvious that while under way the recharge of the two banks is almost never (unless by coincidence) perfectly balanced.
In spite of that, the system seems to have worked well in the last 13 years, not only in mine but also in al other DPs around, so I'm giving it a try for the moment.
And unless it will show a significantly shortened battery life, I'll keep it as it is, 'cause I like its inherent redundancy.
I don't think Annageek would approve it, though...

 

[MapisM]

Would have thought bats need to be SAME amperage in a circuit

Yup, that has always been my understanding too.
Not only that, but as I recall from what Annageek explained us, even one slightly misaligned battery within the same bank can lead to troubles.

That said, the DP recharging system is not consistent with these principles: while the battery charger does have two 24V channels, one for service bank and the other for engine bank, as soon as the engines are turned on the following happens automatically:
- battery charger is disconnected
- both banks are kept connected in parallel
- both alternators (also in parallel) keep both banks recharged while under way

So, it's pretty obvious that while under way the recharge of the two banks is almost never (unless by coincidence) perfectly balanced.
In spite of that, the system seems to have worked well in the last 13 years, not only in mine but also in al other DPs around, so I'm giving it a try for the moment.
And unless it will show a significantly shortened battery life, I'll keep it as it is, 'cause I like its inherent redundancy.
I don't think Annageek would approve it, though...

 

[Portofino]

We have seperate Dom and bat banks ,but for ease they are the identical .
They are charged separately from different outlets on the same charger .
We have a parallel ( some times known as a cross over switch ) on the dash .
Not sure how the two alternators work - presume via a split diode "attack " the starter bank then switch to the doms during a run .Or one for each bank - dunno ? All 24 V systems
Geny has a seperate 12 v tiny car bat with a charger dedicated to it .Also in the E room near it another x over switch to rob 12 v off one of the other banks 24 V .That would be the last chance saloon @ anchor to start the geny + thus chargers .

Bow thruster is a big Vetus motor wired from the E room via large cables From the Dom bank .We don,t have bats under the fwd bunk Just heavey cables running fwd .

The batts are all sealed assume AGM , there no water caps to open and check levels .
It's a very simple boat really
Engine bank is just that engine and nowt else only .
We have quit good instrumentation so I can see the amount each side has depleted and how much the charger is independently putting back ,e.g. Bulk etc
It's a 100 ah charger into 2x 185 for each bank .most I have seen is 40 odd ah going into the dons after a long stay @ anchor .
Engine ( after a run ) hardly registers 1-2 amp so they must be basically fully charged all the time or with in 10 mins of a start up ??

 

[Eren]

Having batteries of different capacities on the same charger should not be a problem ... they will be at different states of discharge anyway.
.

I think the second sentence is a good logic catch.

Basing on this, then I wonder something else, which may be an exact reply to my initial question. The battery chargers have multi outputs. Are these outputs capable of behaving differently? (ie. one output for the service battery bank is at bulk charging state while the other output for engine start batteries can be at float state). If that is the case, then different banks can have different amperages and I can go on with installing the 75 amp Optimas.

Or, trusting on MapisM's DP charger set up, are we too sensitive about this issue? May be, the end result between an "perfect" and "practical" battery setup is quite marginal?

 

[MapisM]

The battery chargers have multi outputs. Are these outputs capable of behaving differently? (ie. one output for the service battery bank is at bulk charging state while the other output for engine start batteries can be at float state).

...

Or, trusting on MapisM's DP charger set up, are we too sensitive about this issue? May be, the end result between an "perfect" and "practical" battery setup is quite marginal?

With my Victron Multiplus inverter/charger, the answer to your first question is definitely yes.
Actually, with these units, it's slightly wrong to say that the channel connected to start batteries CAN be at float state, because according to the manual is works ONLY at float recharge.
Its full power can only be delivered on the primary channel meant for domestic bank, with variable current levels depending on bulk/absorption/float state.

Ref, your last question, based on some boaters feedbacks I gathered so far (some of which weren't even aware that in their boats the recharging while under way works as I described...), the answer to your final questions seems to be yes, since I was told that their batteries normally last 5 or 6 years, which ain't bad at all in a boat, in my experience.
But I'll be able to confirm first hand only in the (hopefully distant!) future, 'cause I installed new batteries on both banks this year... Time will tell!

 

[Eren]

I found this excellent reference regarding this issue:

https://www.victronenergy.com/upload/documents/Book-Energy-Unlimited-EN.pdf

The reference is focused on boat systems, which is therefore very valuable for us.

MapisM: According to the above reference, your start batteries may already been protected with a "battery combiner" which directs the current from the alternator to Dom batteries when it senses that your start batteries are full. Otherwise it is stated that overcharging/overheating would dry out the start batteries in the long run.

For my case, the reference clearly recommends using "spiral type" batteries (Optimas or some Exide models) as they solve the overcharging problems within themselves.

 

[MapisM]

Thanks for the pointer, I'll check that out. :encouragement:

 

[petem]

Could this be why my (single) battery charger only charges the house battery and doesn't charge the dedicated starter battery (each are different amperages)?

 

[No Regrets]

I have one charger 9Sterling) and five batteries. One is 70A/h the rest 110A/h.

The smaller battery is six years old and still going strong! Most of the larger ones have been replaced within the six years! Strange!?

 

[TK Blue MAX]

Could this be why my (single) battery charger only charges the house battery and doesn't charge the dedicated starter battery (each are different amperages)?

I've been told that fairline keep one pair of battery's separate from everything else so they cannot be affected by other faulty battery's ,charger or wiring issues ,therefor always able to start one engine ,and then crossover the other. All the fairlines that we have had have been this way.