question

ian-rob avatar image
ian-rob asked

AGM charging regime.

I want to install 2 x 95Ah AGM batteries on my boat but I am concerned about the charging regime.

Based on the battery data sheet, they require an absorption voltage of 14.4 volts and a float voltage of 13.5 volts. This is mismatched to the output voltage of the alternator fitted to my Volvo D1-30 engine which delivers +-13.9 volts at 2300RPM

  • to get around this, can I use a Victron Orion Smart 12/12 30A to adjust the voltages to the AGM charging regime?
  • to minimise the alterations to the existing cabling, can the Orion just be installed on the existing cables upstream of the splitter or do I need to alter the cabling, as someone has suggested, so that the supply is off the 75Ah AGM start battery (which will act as a buffer)?
  • the shorepower charger similarly has a mismatched outputs. Is there any reason why it’s output couldn‘t be also be regulated by the Orion?

I am rather confused!

Thanks.

battery chargingAGM Battery
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4 Answers
Justin Cook avatar image
Justin Cook answered ·

1. Yes

2. Start battery on input as buffer is the supported method of installation

3. Same as 2, but can't you just reprogram the shore charger with a better profile?

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ian-rob avatar image
ian-rob answered ·

Thanks for your reply.

With the engine running, will both the starter battery and the two domestics batteries, get the voltages they require? Are the batteries charged simultaneously or does the charger first charge the starter battery to full absorption and then switch to the domestics?

Unfortunately, the shorepower charger only has two settings, described as ‘Liquid & Gel’. The Gel setting is right for the absorption stage but wrong for the float stage and vice-versa for the Liquid setting

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Justin Cook avatar image Justin Cook ♦♦ commented ·

The charger does not charge the start battery; the alternator charges the start battery. Once the start battery is at the "turn on" voltage you have configured within the Orion, the Orion turns on and starts pulling current from the start battery to send to the auxiliary batteries.

Have a look at the user and installation manual: https://www.victronenergy.com/media/pg/Orion-Tr_Smart_DC-DC_Charger_-_Isolated/en/index-en.html

When in doubt, please consult a reputable, experienced marine systems installer to help establish the course of action that will best suit your particular use-case!

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ian-rob avatar image
ian-rob answered ·

….. but if the AGM starter battery is charged by the alternator and the alternator only delivers 13.9v rather than the recommended 14.4v, how is it kept in good condition?


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Justin Cook avatar image Justin Cook ♦♦ commented ·

Well you said the start battery is a different battery in any case, so it may have different charge parameters. That's where a marine systems installer could assist, because you may need an external alternator regulator on the system for best performance, or you may be fine with what you have - no way for us here to tell.

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ian-rob avatar image
ian-rob answered ·

The starter battery is 75Ah AGM with same charge parameters but I will try and find a marine installer as you suggest with expertise in Victron kit. Thankyou.

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