Can I parallel battery chargers?

[rigpigpaul]

Hi All, I want to increse my battery bank to 400amps. I currntly have a 20amp Dolphin charger. Can I fit another 20 amp charger in parallel with the existing charger. I am trying to avoid buying a 40 amp charger.
rgds RPP

 

[maby]

It probably depends on how "intelligent" the chargers are. If they are very basic constant output chargers of similar characteristics, you may get away with it. Most high specification chargers fitted to boats are "intelligent" chargers that adjust their output to match the perceived state of charge of the battery and may go into a variety of maintenance modes with variable outputs. Under those circumstances, I would think there was a real risk of the two chargers fighting each other - at least you would lose any kind of intelligence, and they could overload each other.

 

[ianj99]

Hi All, I want to increse my battery bank to 400amps. I currntly have a 20amp Dolphin charger. Can I fit another 20 amp charger in parallel with the existing charger. I am trying to avoid buying a 40 amp charger.
rgds RPP

You don't have to upgrade the charger - unless charging time is limited.

 

[TrueBlue]

Thinks,
Is it worth constructing (bit of soldering etc) a diode block so that the chargers are isolated one from another.

The real question is - given that one (I) assume the chargers are left on for a considerable period of time i.e. for "the week" after a weekend's boating - then the batteries have all that time to be recharged? So more welly is not really needed.

Have I missed a point ??

However, if the bigger battery charger is needed 'cos you dive for cover overnight (back to the mains supply) ready for the next day's consumption, THEN to my my mind an extra battery might be more practical / cost effective.


I've always gone on the basis of charge slowly / use at "whatever". It's not really a good plan to throw a lot of kit at the problem - just because it's easy to fit. Better always to go to the real requirements -

which you haven't defined.................

I wait for further information.

Fin.

 

[Jamesuk]

Hi All, I want to increse my battery bank to 400amps. I currntly have a 20amp Dolphin charger. Can I fit another 20 amp charger in parallel with the existing charger. I am trying to avoid buying a 40 amp charger.
rgds RPP

Yes. We have two Mastervolt chargers that throw in up to 180 amps on a bulk charge, Then one drops out as and when the batteries get to the aborption phase As for wiring. ooo consult the manual.

 

[rigpigpaul]

Can I parallel battery chargers

Thanks for all the replies.
TrueBlue---I thought the rule of thumb for battery a charger size was 10% of the battery bank value. My base is Bodrum area so it will be a couple of days at anchor then onto a jetty with power for a couple of days.
rgds RPP

 

[noelex]

Thanks for all the replies.
TrueBlue---I thought the rule of thumb for battery a charger size was 10% of the battery bank value. My base is Bodrum area so it will be a couple of days at anchor then onto a jetty with power for a couple of days.
rgds RPP

There are rules of thumb like this, but often it is mystery why they develop or continue to be quoted. Very slow charging can result in stratification of the electrolyte, but in practice it's rarely a problem. An occasional equalisation charge (if OK for your batteries) will generally undo this.
If you drain your batteries down to 50% then 48 hours on a 20 A charger is enough to get them back up to very close to 100% ( assuming you only have a mild load on the batteries while charging). If you spend only short periods on shore power, or use a high load from the batteries while connected to shore power then adittional charging capacity is worthwhile. Multiple chargers are OK.
Get a good battery monitor and check your SOC. If you are getting back to fully charged with your existing battery charger I would not go to the expense of an addition one.

 

[William_H]

Battery chargers

The idea of a diode block is probably not a good one with many moder chargers needing to see the battery voltage before it decides what to do by way of charge. Of course with old steam chargers no problem but any regulated charger will see the diode volt drop and charge to a lower voltage hence % of charge.
As said try your bigger battery bank with the 209 amp charger. Depending on your needs it should be fine. olewill

 

[nigelmercier]

Interesting to find this thread via Google, as I have just had this conversation with CTEK regarding their M300 25A charger:

You can parallel connect 2 pc M300, then you get 50A in charge ...
Surely the chargers would conflict with each other?
No, there is no conflict between chargers. You connect each charger directly on the plus and minus terminals.
But how does the charger “know” what the state of the battery is, if there is another charger in parallel?

I'm waiting for their reply ...

 

[ianj99]

Interesting to find this thread via Google, as I have just had this conversation with CTEK regarding their M300 25A charger:

You can parallel connect 2 pc M300, then you get 50A in charge ...
Surely the chargers would conflict with each other?
No, there is no conflict between chargers. You connect each charger directly on the plus and minus terminals.
But how does the charger “know” what the state of the battery is, if there is another charger in parallel?

I'm waiting for their reply ...

Both chargers will see a drop in current as the battery charges up and as you are only needing both chargers for bulk charging, it doesn't matter if one switches mode - no current will ever flow from one charger to the other.

Ie If one charger should switch to absorption or float, it won't matter as the other will continue until it switches mode as well - only one charger is needed in the float or absorption phase when currents are very low.

 

[nightjar]

I have 2 X 30 AH Sterling chargers wired in parallel. Normally use only one, but where quick recharge is required both are used. No problems with this setup over 12 years.

 

[pcatterall]

I have 2 X 30 AH Sterling chargers wired in parallel. Normally use only one, but where quick recharge is required both are used. No problems with this setup over 12 years.

That was going to be my response; have the second one ready to switch in if you need a quick charge.

 

[Mistroma]

I also wondered about this last year but didn't follow up. Searches at the time threw up everything between it will be fine and it could damage the chargers. I remember being advised that it would be OK as long as both chargers were identical.

My need was mainly to cut initial 50%-85% time with mains charger via Honda genny and then switch back to one charger if putting more in (i.e. short stink on shorepower).

I had realised that 2 x dumb chargers might work well but 2 x smart chargers might "hunt" but I thought it would be fine when batteries were pretty much taking all current available from both chargers. Dumb chargers with 30-40A didn't seem common but variable "power supplies" seem to be quite cheap. I discarded the option of using a cheap power supply on a timer because I thought it wasn't a good option (several reason but I won't bother to list them).

I have a Cristec 40A charger and had thought about adding a cheap 30A-40A charger purely for use when running the generator. However, I shelved the idea due to the lack of solid information. Some of the nay sayers were obviously talking complete rubbish and obviously clueless but a few did sound credible.

I've seen this unit on eBay and would be tempted if I could be convinced it wouldn't cause any harm and would give me 65A for a couple of hours when needed. I wouldn't be able to fit 2 identical chargers.
http://www.ebay.co.uk/itm/FULLY-AUT...tEquipment_Accessories_SM&hash=item1e76a4ce8e

I do remember reading suggestions about putting in diodes to isolate chargers from each other and that didn't seem to be viable for reasons given. Pity, as I actually have a redundant isolation diode sitting on the boat (100-150W).

 

[srm]

Why not use a solar panel and have the batteries topped up during the day? We have a 400AH domestic bank and can go for a week or so at anchor without it dropping below 80% on the west coast of Scotland with solar panels and a wind turbine (but as we usually pick sheltered anchorages the wind doesn't contribute much). Should have plenty of solar energy around Bodrum in the sailing season and the panels will still charge when on shore power so no need for a second mains charger.

 

[Mistroma]

Why not use a solar panel and have the batteries topped up during the day? We have a 400AH domestic bank and can go for a week or so at anchor without it dropping below 80% on the west coast of Scotland with solar panels and a wind turbine (but as we usually pick sheltered anchorages the wind doesn't contribute much). Should have plenty of solar energy around Bodrum in the sailing season and the panels will still charge when on shore power so no need for a second mains charger.

Unfortunately, not much help to me as I'm not in Bodrum, my wind-gen and 125W solar won't keep up with usage for long periods. I'll be on board for 6-7 months and although solar and wind will keep up in mid-summer they are a short early and late season. Batteries do get down to 50%-55% and generator needs long runs to get back to 85% with only 40A charger. No problem when motoring but it is a pain if anchoring in one place for a long time (or hopping from bay to bay under sail). I'd also like to make better use of shorepower from time to time without having to hang around the marina for longer than I really need to. I like to have a backup when possible and a second charger would be better than my current fallback (motor more often).

I wouldn't have posted if my boat's power generation, storage and usage were fine with the current setup. Yes, I could add more solar (if I could find space) but would need a lot more to cover early and late season.

 

[srm]

Unfortunately, not much help to me as I'm not in Bodrum, .

Ooops Sorry for the confusion Mistroma; I was responding to the OP, who said he was based in Bodrum.

Your comment makes it look as if the west coast of Scotland and Scandinavia is better for solar than Galacia as my panels only total 150W, with only one in good light at any time given their distribution. More likely we have very different loads at anchor, though my fridge is on 24/7 while we are on board - usually for 5 or 6 months and we aim to motor and use marinas / shore power as little as possible. I have never had my batteries below 70% capacity even after night sailing and have only resorted to the towed generator on a couple of occasions.