# Looking to Upgrade DC system

Discussion in 'OnBoard Electronics & Controls' started by mydauphin, Feb 21, 2012.

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### mydauphinSenior Member

Presently I have a single DC system consisting of two 12 volt batteries connected in series to provide a 24 volt circuit and two 12 volt circuits. I have a 24 volt charger/inverter that connects to the two. I also have solar panels that charge one for the 12 volt batteries.

I am looking to create 2 more similar systems on my boat, one for the engine room and one for the bow, and the original house. So I would have a total of 6 batteries making 3 banks of two 12 volt batteries. I hope you understand my diagram. Note: this is a large boat and my engine do not require electricity to start or run.

My question are these;
If two batteries are in series, does the weaker one charge the lower voltage one?
When I parallel the 24 volt battery banks, would they charge/balance even each other?

I guess the only way to check individual battery voltage is to disconnect battery from parallel?

Anyway, any and all comments are welcomed.

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2. Joined: Jan 2009
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### pistnbrokeI try

In series when charging the better battery would get over charged which reduces its life.
always use matched batteries in both age and make and type..you will need to rate your alternators at 25A per 100AH of capacity . Multiple alternators are normal. If you have a 24v alternator then the 25A will charge 2 batteries as they are in series.

If you parallel the three 24v banks then over time they will discharge one another BUT if its used ..ie charged daily or even weekly then should not be a problem . Batteries in parallel left for a long time is not a good idea ..depends on there conditon ..again should alll match for age .type etc

Yes to check voltage you would need to disconnect but if you are looking for state of charge a hydrometer is better.

I dont know how you are getting 12v but if its by loading one of the batteries you have in series to give you 24v ..bad idea ..this will result in an unbalanced re charge and short battery life ...

The experts on house battery systems are at www.canalworld.net

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### CDKretired engineer

A small addendum to pistbroke's true words:
There are 2 ways for batteries to show signs of age, loss of active plate surface or a low resistance path (or complete short) because of conductive sludge.
During charging the first behaves like a good battery, but a much smaller one. The second draws the charge current of a much larger battery without ever reaching a fully charged state.
Both are poor candidates for parallel or serial wiring unless swapping batteries is your hobby.

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### rasorincSenior Member

It ia better to connect all your batteries in a series for charging rather than 3 groups of two. You guys probably know all this but I post it for the electrical dunses like me.
http://www.smartgauge.co.uk/batt_con.html The third method shown is the overall best for more than 2 batteries. my 2 bits.

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### pistnbrokeI try

re the above post ..it depends if you are doing constant voltage charging or not ...if its from an alternator its constant voltage so batteies in series other than 2x12v is not an option..if you are to put a high load on these batteries each 24hrs then you need a good engine driven alternator system to charge them and no no no no no diode split charging systems please !!!!

A UK canal boat with say 600AH at 12v would run its engine/alternator 8 hrs a day to replenish the daily usage ....

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### jamesgyoreSenior Member

Wow, what a fantastic resource! Thank you.

I've been lucky enough to pick up an obscene number of new batteries from a write-off Nissan forklift truck (one charge before I purchased them), which I know to be superior deep cycle devices.

I was not sure how I might put them to good use on my boat, frankly I still don't, but your link has given me greater insight.

With a little help, these batteries will not only serve as ballast with a secondary purpose, but the ridiculous amount of stored energy will satisfy every electrical mod-con with amps to spare with infrequent re-charging.

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### pistnbrokeI try

Quote ....infrequent re-charging.

Recepie for disaster .....

8. ### FrostyPrevious Member

Bad batteries swell, yes swell,-- ie I mean gets fat.

The outsides of the batt at the end is not flat.

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### jamesgyoreSenior Member

I there,

How so? While I'm not quite done with my electrical needs calculations, I'm thinking 2~3 days to run down to about 75~80% before needing to think about charging.

10. ### FrostyPrevious Member

That would be a life of hell if you were a battery. Imagine getting fed every 3 days and still having to plow a field.

An Automatic battery charger will consiquently add years to a life of a batt.

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### sdowney717Senior Member

batteries that stay continually undercharged have shorter life.

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### pistnbrokeI try

if they never go over 13.6v about 6 months....
discharge below 50% bad news

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### BertKuSenior Member

No, but you need to put 2 heavy type of Zenerdiodes made up from 4 x 2N3055 parallel and again another 4 x 2N3055 parallel for the bottom battery, which each is driven in the paralled base of the transistor with each a serial resistor of 10 Ohm and one 15 Volt 7815 regulator. In that way each battery will not be overcharged with a too high voltage , if one of the two batteries is weaker or older and thereby reducing the lifetime. I have batteries which are already charged for 8 years like that.

Yes, and that would be bad. The best is in that case to use schottky diodes between de plus poles of the 24 Volt system. As explained in thread: "1or2 batteries by gadget300 go to the photo's in the last thread".
No, if you use a shottky diode between the + poles, you can measure the batteries one by one, without disconnecting or stopping your gadgets connected.

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### pistnbrokeI try

Jesus I Feel Ill all this diode parallel **** is all vespa scoota technology ..just get good batteies and wire them us in series parallel as required and sleep easy in your bed ....all this makes me feel quite ill .....

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### BertKuSenior Member

Untill a half year later , one of your batteries goes bad and you are happily charging two in series placed batteries. One faulty one and good one.Then I feel very ill, to see the other good battery also to go bad.
Bert

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