Lithium battery bank as auxiliary starter battery

[Deividas]

Thinking about my Lithium house bank installation. Theoretically, Lifepo4 batteries (2x100Ah Renogy) could be used as auxiliary starter batteries in case the starter battery is discharged.



Will my setup work? Could I interconnect charged Lithium and discharged Lead-acid batteries in parallel to start an engine? And after the engine will start to disconnect the house bank?

[Adelie]

Yeah, looks like it would work.

Frankly, a regular FLA house bank could be used to start the engine. Some folks do without a separate starting battery and always start from the house bank.

This does away with the complication of a special charging system for the starting battery:
A. 2nd alternator
B. ACR
C. Echo charger
D. ????
Frankly you could toss out a 30W panels and a cheap PWM controller to keep the starting battery up. On a big hard starting motor you’ll use about 1Ahr for each start. On a small easy-starting motor you’ll use 1/4(?) of that. The 30w panel will be put in out about 9Ahr/d in lower latitude areas and high lays during the summer. Unless you have a starting problem even a 10W panel would do the trick.

[Adelie]

Probably want to disconnect starting battery before connecting house or house will start recharging starter batt.

[Pitchondesign]

I'm no expert, but starters draw very high amperages, in the hundreds of amps, for a very short time. Typical lithium battery BMS systems will disconnect above a certain amperage, depending on the battery. It seems that you system with two 100 ah batteries might trip those BMS's. Might want to check.

[Deividas]

Originally Posted by Adelie

Probably want to disconnect starting battery before connecting house or house will start recharging starter batt.

This is how I see this situation.
I can't disconnect the start battery because when the engine will start working I will not be able to disconnect the house bank from the engine. Without a connected battery I will cook my alternator.
And the question is if it's a problem if this is only for a short time house bank is interconnected with start bank? Just until the engine will start?

[Adelie]

I meant that if the starting battery is drawn down enough to not be able to crank the motor the switch over to house for starting and leave starter batt completely out of circuit.

Charging start batt and cranking engine at same time is going to make a big load in house batteries even bigger.

[Pitchondesign]

If you connect your lithium bank directly to a discharged lead acid battery, significant amperage will flow. The exact current flow will depend on the charge levels of each bank. The cables between the batteries will need to be fused, if not already, and you need to consider the possibility of BMS cut out, from too much amperage flowing.

The standard set up is to allow a Battery to Battery charger, using your lithiums as a power source, to charge the start battery correctly. The B2B charger will take longer but won't fry anything.

[facciatosta]

Originally Posted by Deividas

Thinking about my Lithium house bank installation. Theoretically, Lifepo4 batteries (2x100Ah Renogy) could be used as auxiliary starter batteries in case the starter battery is discharged.



Will my setup work? Could I interconnect charged Lithium and discharged Lead-acid batteries in parallel to start an engine? And after the engine will start to disconnect the house bank?

Not good idea, in theory
1) the DISCHARGED starter battery will start sucking current from the house batteries and may sink the voltage of the house batteries. If in addition to this you try to crank the engine in this situation you may overtax the house battery.

2) Before using the house batteries to start the engine without starter battery you need to check the spec of the house battery for CCA - what maximum current house battery can produce and sustain. My understanding is that in general lithium batteries are not designed for high currents but it may not be a case with Lifepo4.

You can try to connect house and starter batteries in parallel and wait until starter battery will recharge then disconnect the house battery and try to crank the engine

[facciatosta]

Originally Posted by Deividas

This is how I see this situation.
I can't disconnect the start battery because when the engine will start working I will not be able to disconnect the house bank from the engine. Without a connected battery I will cook my alternator.
And the question is if it's a problem if this is only for a short time house bank is interconnected with start bank? Just until the engine will start?

There are battery switches like Blu Sea Systems that allow to switch between the batteries without interruption the circuit as long as you do not switch it to the OFF position
https://www.bluesea.com/products/600...y_Switch_-_Red

[Deividas]

Originally Posted by facciatosta

There are battery switches like Blu Sea Systems that allow to switch between the batteries without interruption the circuit as long as you do not switch it to the OFF position
https://www.bluesea.com/products/600...y_Switch_-_Red

Thanks.
But anyway there will short moment when both batteries are connected parallelly.

[kirklkjb]

You also run the risk of blowing up your alternator by connecting to the engines alternator. The alternator is designed to charge for a short period of time at much less than the 100-200A that your LI battery can charge at. The best suggestion is a battery to battery charger or you can buy a simple hand held LI jump starter that is designed for this kind of thing and have it ready to go. That way you don't blow up your alternator, fry the cabling or other nasty things by mixing up the start and house batteries. Not an endorsement just an example. They provide a high current for a short time. https://www.amazon.com/gp/product/B0...53PO7BYQ&psc=1

[CNC30sailor]

I solved my emergency starting issue with a portable Lithium booster pack. It came in a nice case with high quality cables. 1400 cranking amps, a flashlight, 12V and 5V outputs. $130.00 on sale. Works like a charm. Already saved the day a couple of times.

[roland stockham]

Simplest and cheapest most versatile and reliable way to set up an emergency start system is a pair of jump leads!! Why complicate things?

[kirklkjb]

Originally Posted by roland stockham

Simplest and cheapest most versatile and reliable way to set up an emergency start system is a pair of jump leads!! Why complicate things?

It's just not that simple when mixing battery chemistries with vastly different current delivery and acceptance capabilities.

You may want to do it in an emergency and disconnect as soon as the engine starts but any damage could already be done or in the worst case scenario your boat could be on fire by then depending on how badly it turned out.

I still think a good quality portable starter as suggested is the best solution or a battery to battery charger. Either should do the job just fine with little risk to either sets of battery systems.

[Deividas]

OK, OK. You convinced me. Going to order this - https://www.amazon.de/dp/B07MVY7K43/...pa_dk_detail_0

Thanks