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steves avatar image
steves asked

My MPPT / Orion sytem cycles the battery. Is this a problem?

I have a 100 W panel charging a 100AH lead acid starter battery (SB) through a Smart MPPT. When the 'engine on' voltage signal is given an Orion DC-DC takes input from the SB and charges a 300AH house bank (HB). (Currently also lead acid but possibly Lithium in the future.)

If the HB has a significant draw it causes the SB to give the 'engine off' signal and until the SB has recovered, a few seconds usually , the Orion sleeps. This results in the voltage in both HB & SB cycling around near the float voltage until either the demand drops or the panel provides enough power to keep everyone in the absorption phase, or later float.

My QUESTION is this. Does this cycling have any detrimental effect on either the batteries or the Orion?

This is of course an issue when the boat engine is off. When the engine is on the alternator has enough power to hold the start battery up whatever the Orion chooses to draw. Most of the time boat engines are not running however.

orion dc-dc
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ingo21 avatar image ingo21 commented ·
why are you charging the SB with the solar panel and not the HB?
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steves avatar image steves ingo21 commented ·

Its a power boat so when underway both batteries are charged. I have set it up this way for two reasons.

i) I want to be in doubt the starter battery is fully charged. (If set up the other way and both batteries were down it would favour the HB)

ii) My Alternator is not ideal for charging Lithium. I want the option to switch in the future though since I wrote my query I increasingly doubt I will. Even for AGM HB I can give a better charging profile this way.

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2 Answers
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bostonmarinervelectrical answered ·

The Orion outputs a set amperage. When the source battery reaches a charge voltage, the Orion turns on, draws amperage from the source battery, and charges the other battery until source voltage drops below charging voltage. Unless your solar output amperage is equal to or greater than the Orions rated amp draw, it will eventually draw down the source battery, lower its voltage and turn off.


I'd guess that you are decreasing the lifespan of the starter battery. In my opinion, you'd be better off moving the mppt to the house bank.

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steves avatar image
steves answered ·

Yes, your description of how it works is exactly right, but not a problem. I can set it so if it can not hold the float voltage it just turns off from delivering SB > HB. That is why it ripples though, hence my question above:

My QUESTION is this. Does this cycling have any detrimental effect on either the batteries or the Orion?

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