marine battery chargers are they worth the difference in price

[geem]

Sorry - a 400Ah needs about a 100Ah charger - that's 15% of AH capacity = 60 amps + 5% for house loads = 20 amps. Always go higher, so you need a 100 amps charger - I've never seen an 80 amp charger!!!!

AGMs need a minimum of 20% of Ah capacity +5% = 25%, so again = a 100A charger.

I have corrected my error.

Why?
One size doesn't fit all. If you have no other form of charging then maybe so but lots of boats have solar, wind, towed and of course engine alternator of varying capacity. Some boats have just a 100w solar panel others have 1500w of solar. How can you say you must have 15% of battery capacity? You are not taking in to account the use of the boat. Two identical boats can have hugely different use characteristics.

 

[sailinglegend420]

I was not going to reply, but must ask, do you know the theory behind a VSR? ....

That's a bit of an insulting comment!

I don't understand from your post what I have said that you disagree with.

My observations on my boat are as stated in my post, charge the starter battery first and I see 100+ amps discharged as the VSR closes, then the starter battery voltage falls as the service bank is low and the VSR disengages - chatter - chatter .... as this is repeated. This is not good for the starter battery as it is just like another engine start cycle, and not good for the VSR relay repeated turning on and off.

Charge the Service battery first and chattering will never happen. The starter battery can probably start the engine 10-20 times before it needs re-charging as less than 1% of its Ah capacity is used on each start cycle.

So what have I suggested in my post that has upset you?

 

[halcyon]

That's a bit of an insulting comment!

I don't understand from your post what I have said that you disagree with.

My observations on my boat are as stated in my post, charge the starter battery first and I see 100+ amps discharged as the VSR closes, then the starter battery voltage falls as the service bank is low and the VSR disengages - chatter - chatter .... as this is repeated. This is not good for the starter battery as it is just like another engine start cycle, and not good for the VSR relay repeated turning on and off.

Charge the Service battery first and chattering will never happen. The starter battery can probably start the engine 10-20 times before it needs re-charging as less than 1% of its Ah capacity is used on each start cycle.

So what have I suggested in my post that has upset you?

I was not trying to insult you, just explain how and why a VSR operates.

Chatter, I tried to explain why it should not happen, but in the past it is due to bad design, one large manufacturer used to engage at 12.8 volt and drop out at 12.8 volt, thus chatter.

Brian

 

[sailinglegend420]

I was not going to reply, but must ask, do you know the theory behind a VSR ?

I have read this thread again and I really don't understand what you are saying in places!

...Engine battery normally has a higher charge level, so needs a higher charge voltage so takes no charge till voltage reaches it's charge voltage. At this point the service battery is close to the capacity of the engine battery and both take a current as they need....

This I'm afraid is totally confusing. Do you mean State of Charge (SoC) - in which case this is impossible. How can a service battery that is at say 50% SoC and maybe 5 times larger capacity than the starter battery - which is at about 99% SoC - suddenly have the same capacity or SoC?

Charging batteries is very involved and needs a scope to track actual current and voltages, not just what does the multimeter read.

This is again totally wrong! A cheap digital ammeter is needed.

 

[lw395]

I was not trying to insult you, just explain how and why a VSR operates.

Chatter, I tried to explain why it should not happen, but in the past it is due to bad design, one large manufacturer used to engage at 12.8 volt and drop out at 12.8 volt, thus chatter.

Brian

Even if there is plenty of hysteresis in the pull in/drop out voltages, some were prone to dropping out due to the load of the starter, then immediately pulling in again as the house battery goes back to higher voltage, especially if these a solar panel charging the house battery.

 

[lw395]

Sorry - a 400Ah needs about a 100Ah charger - that's 15% of AH capacity = 60 amps + 5% for house loads = 20 amps. Always go higher, so you need a 100 amps charger - I've never seen an 80 amp charger!!!!

AGMs need a minimum of 20% of Ah capacity +5% = 25%, so again = a 100A charger.

I have corrected my error.

I think the 20% of AH is a maximum not a minimum. So shoving in 25% because the fridge is turned off might not be a good plan?

 

[halcyon]

Even if there is plenty of hysteresis in the pull in/drop out voltages, some were prone to dropping out due to the load of the starter, then immediately pulling in again as the house battery goes back to higher voltage, especially if these a solar panel charging the house battery.

We always had an interface to the starter motor, dropped out the relay if secondary charge sources were in operation, so service bank never had starter motor loads, unfortunately people have not incorporated this feature.

Brian

 

[PaulRainbow]

Don't get the +5% for house loads

My domestic bank is 390ah, so i need 19.5a of battery charging capacity to cope with domestic loads ? What if i double my battery capacity, do i need to fit a bigger charger, how does my domestic requirements vary because of battery bank capacity ?

My mains charger is actually 30a, slightly less than 10% of my battery capacity, during the Winter it manages quite nicely.

During the Summer, my solar panels run everything on the boat without shore power. Max output of the controller is 15a.

 

[PaulRainbow]

Sorry - a 400Ah needs about a 100Ah charger - that's 15% of AH capacity = 60 amps + 5% for house loads = 20 amps. Always go higher, so you need a 100 amps charger - I've never seen an 80 amp charger!!!!

AGMs need a minimum of 20% of Ah capacity +5% = 25%, so again = a 100A charger.

I have corrected my error.

You need to get out more

https://www.mastervolt.com/products/chargemaster-24v/chargemaster-24-80-3/

https://www.es-store.co.uk/product_...tery-Charger&cat_desc=&cat_id=70&show_menu=21

As for needing a 100a charger with 400ah battery bank .............. seriously ?

 

[geem]

Don't get the +5% for house loads

My domestic bank is 390ah, so i need 19.5a of battery charging capacity to cope with domestic loads ? What if i double my battery capacity, do i need to fit a bigger charger, how does my domestic requirements vary because of battery bank capacity ?

My mains charger is actually 30a, slightly less than 10% of my battery capacity, during the Winter it manages quite nicely.

During the Summer, my solar panels run everything on the boat without shore power. Max output of the controller is 15a.

Totally agree. These quoted ‘must haves’ are useless if you know nothing about boat use. We have 1000amp domestic bank, 380w of solar, Duogen for wind and towing. A generator with two shore power chargers. We hace nowhere near 20% of battery capacity on our charger but we dont really use the charger as solar and wind/ towed does it for us. People tell is we wont be fully charging our batteries but the hydrometer says otherwise. Fully charged everyday.