LiFePO4 reference diagram, Alternator version

[Zonker]

Originally Posted by newhaul

Ok here's a question . Can you parallel lifepo4 and low lead start bank to boost lead enough to start a tamd41 engine

Think about the current flowing from Li to lead bat. Don't do it.

[s/v Jedi]

Originally Posted by newhaul

Ok here's a question . Can you parallel lifepo4 and low lead start bank to boost lead enough to start a tamd41 engine

If you heck the reference diagram in the first post of the thread, you will see no such option. There should be two start batteries with an isolation switch; I use a four position OFF, A, B, A+B switch for that.

In such a setup I also recommend to have one battery about 3 years older than the other so that you have a rolling replacement routine

[Zonker]

Originally Posted by s/v Jedi

If you heck the reference diagram in the first post of the thread, you will see no such option. There should be two start batteries with an isolation switch; I use a four position OFF, A, B, A+B switch for that.

In such a setup I also recommend to have one battery about 3 years older than the other so that you have a rolling replacement routine

Are you an electrical engineer or a handy man ? ...

[newhaul]

Originally Posted by s/v Jedi

If you heck the reference diagram in the first post of the thread, you will see no such option. There should be two start batteries with an isolation switch; I use a four position OFF, A, B, A+B switch for that.

In such a setup I also recommend to have one battery about 3 years older than the other so that you have a rolling replacement routine

I'm thinking worst case scenario emergency hopefully never done . Not normal operation situation.

[newhaul]

Originally Posted by Zonker

Think about the current flowing from Li to lead bat. Don't do it.

The current flow is not an issue the lead will only accept at rate it will accept that's the beauty or the problem of peukert effect.

[Zonker]

Originally Posted by newhaul

The current flow is not an issue the lead will only accept at rate it will accept that's the beauty or the problem of peukert effect.

>> parallel lifepo4 and low lead start bank


So if you have a "full" li bat and an "empty" lead bat - it's gonna cook the lead bat.



If the lead bat is cooked, then Peukert will have no any effect.

[newhaul]

Originally Posted by Zonker

>> parallel lifepo4 and low lead start bank


So if you have a "full" li bat and an "empty" lead bat - it's gonna cook the lead bat.



If the lead bat is cooked, then Peukert will have no any effect.

Explain that in technical terms .
The lifepo4 is 100ah 12v and the start is 220ah fla gc2. Not dead but to low to snap the engine . I'm only talking about approx 30 seconds in parallel. You know like a jump pack

[s/v Jedi]

Originally Posted by Zonker

Are you an electrical engineer or a handy man ? ...

You may want to reconsider the way you discuss things with me because I don’t like the tone of it here.

I am an EE incl. micro electronics design.

[Zonker]

Originally Posted by newhaul

Explain that in technical terms .
The lifepo4 is 100ah 12v and the start is 220ah fla gc2. Not dead but to low to snap the engine . I'm only talking about approx 30 seconds in parallel. You know like a jump pack

If your Li Bat consists of 4 cells -> if fully charged -> ca. 16V


Your lead bat might be at 11V -> this is a huge diff of 5V and since the lead bat has very low resistance, the current is going to be very high because the Li bat can deliver it.


If I were you: have the neg. pole of the lead bat already attached. Crank your engine up only with the Li bat. After the engine runs, quickly swap the pos. pole of the Li with the pos. pole of the lead bat.


Hope this is technically good enough ...

[newhaul]

Originally Posted by Zonker

If your Li Bat consists of 4 cells -> if fully charged -> ca. 16V


Your lead bat might be at 11V -> this is a huge diff of 5V and since the lead bat has very low resistance, the current is going to be very high because the Li bat can deliver it.


If I were you: have the neg. pole of the lead bat already attached. Crank your engine up only with the Li bat. After the engine runs, quickly swap the pos. pole of the Li with the pos. pole of the lead bat.


Hope this is technically good enough ...

That solution is not possible as the lifepo4 drop ins have a 150 amp bms which by itself will not carry the load of the starter that's why staying with lead for starting to begin with.
I'm looking at using the lifepo4 bank like a jump pack if ever needed ( hopefully never need)
Or should I just carry a lipo portable jump pack?

https://www.amazon.com/dp/B015TKSSB8...REALw_wcB&th=1

[Zonker]

Originally Posted by newhaul

That solution is not possible as the lifepo4 drop ins have a 150 amp bms which by itself will not carry the load of the starter that's why staying with lead for starting to begin with.
I'm looking at using the lifepo4 bank like a jump pack if ever needed ( hopefully never need)
Or should I just carry a lipo portable jump pack?

https://www.amazon.com/dp/B015TKSSB8...REALw_wcB&th=1

Ah ... so your Li bat has a "limiter". Portable jump pack is always good but I fear it's empty when you need it (happened to me) ... Murphys law ...


But what you can do is - have a super capacitor jump starter (or installed it fixed). It can be charged very quickly from your Li bat or even from a "weak" bat which has voltage but can't do high current.


[important: I am not affiliated to any of these "products"]



https://youtu.be/GPJao1xLe7w?si=4an4mQDJNmH1Ik2a


or for example


https://www.amazon.ca/Acmount-Capaci.../dp/B0BZV4HZSQ


[edit: don't buy this jump starter, was just the first hit with Google! Way too expensive!]

[CaptainRivet]

Originally Posted by newhaul

Explain that in technical terms .
The lifepo4 is 100ah 12v and the start is 220ah fla gc2. Not dead but to low to snap the engine . I'm only talking about approx 30 seconds in parallel. You know like a jump pack

Yes you can do that but risk killing mosfet in your 150A BMS as the first connection spike will be high. most likly ok but a chance is there so use a smaller diameter cable to limit that. Then no problem. If you have access to the cells simply bypass the BMS for that and start from Lifepo4, it's emergency and cells can do it.
Recommend change BMS to 300A JK and you can directly start from Lifepo4 by just flipping the switch. Costs the double then your starter pack which is empty when you need it. Always recommend to get biggest current rating with mosfet BMS that is available, the cost difference are 30 till max 50 Euro and well invested even if you just use 100AH cells.

[newhaul]

Originally Posted by CaptainRivet

Yes you can do that but risk killing mosfet in your 150A BMS as the first connection spike will be high. most likly ok but a chance is there so use a smaller diameter cable to limit that. Then no problem. If you have access to the cells simply bypass the BMS for that and start from Lifepo4, it's emergency and cells can do it.
Recommend change BMS to 300A JK and you can directly start from Lifepo4 by just flipping the switch. Costs the double then your starter pack which is empty when you need it. Always recommend to get biggest current rating with mosfet BMS that is available, the cost difference are 30 till max 50 Euro and well invested even if you just use 100AH cells.

Drop ins on the crab boat not my own pack. And thinking worst case only