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solarwind

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Joined: 03/02/2008
Location: South Africa
Posts: 51

Posted: 11:52am 29 Nov 2014

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Is anyone able to comment on the disadvantages of parallel connecting A) lead-acid cells and B) Ni-Fe cells?

You don't have success until you've tried it!

VK4AYQ
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Joined: 02/12/2009
Location: Australia
Posts: 2539

Posted: 12:49pm 29 Nov 2014

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Hi Solawind

The two types have different charge discharge characteristics from memory the NIFE cells have a higher internal resistance so when connected in parallel the lead acid battery would do more work than the NIFE cells.
Nife cells are not as critical voltage wise as FLA cells and can be undercharged or over charged without damage whereas FLA cells need charge and discharge parameters closely controlled if you expect a reasonably long life, to me it would be like hooking a horse and a donkey to a plough and expecting good results.

I have used both types in the past but not connected together.

All the best

Bob

Foolin Around

solarwind

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Joined: 03/02/2008
Location: South Africa
Posts: 51

Posted: 09:42am 30 Nov 2014

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Thanks Bob,
What do you think of the idea to have them charged using isolation diodes and also isolating diodes feeding the load?

I know there is a loss introduced by using the diodes, but I might gain the extra Ah.
Your take on this?
Regards,
Johann

You don't have success until you've tried it!

VK4AYQ
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Joined: 02/12/2009
Location: Australia
Posts: 2539

Posted: 03:05pm 30 Nov 2014

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Hi Solar wind

The charging is not so much the problem as NIFE cells are quite forgiving but the discharge side is more the problem as the FLA batteries will discharge faster than the NIFE cells and may discharge deeper than is good for them, if you monitor the depth of discharge on the FLA cells carefully you could avoid this effect. Depending on the load you are pulling you could use a voltage switching controller to cut out the lead acid batteries before they over discharge. I think that diodes alone are not going to control the amps out of each section, as for the charge cycle the both batteries would be OK in parallel to 15.5 volts of your regulator, for discharge the diodes in series with the FLA will introduce a little extra resistance but it may not be enough to prevent an over discharge.

Also I not that the two batteries have different AH capacities to further complicate matters

All the best

BobEdited by VK4AYQ 2014-12-02

Foolin Around

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