ArgoFet Output Question

[Zoodles]

My new install includes an Argofet Isolator with outputs to a SLA 'Reserve/Start' battery and LifePO4 House battery bank.

Although the battery banks will be almost always isolated, there is the possibility I may join the battery outputs together in an emergency start situation where I need additional power from the 'House". (The engine starter is connected to 'Start' battery)

My question is this: If the Argofet outputs are shorted together when the batteries are paralleled, will that damage the FET's on the isolators output??

Thanks

[GordMay]

That might be a good question for the equipment manufacturer.

Victron ➥ https://www.victronenergy.com/contact

[goboatingnow]

Firstly paralleling LFP and a LA battery is never a good idea.

The paralleling should take place between the Argofet(s) and the battery not after the argofet because these isolators are unidirectional and you could have current flowing between the batteries when paralleled and this could damage the Argofet ( though the body diode of the power mosfet is usually quite robust )

[Baronkrak]

Originally Posted by goboatingnow

Firstly paralleling LFP and a LA battery is never a good idea.

The paralleling should take place between the Argofet(s) and the battery not after the argofet because these isolators are unidirectional and you could have current flowing between the batteries when paralleled and this could damage the Argofet ( though the body diode of the power mosfet is usually quite robust )

Interesting statement can you expand on the subject?

https://www.cruisersforum.com/forums...la-257943.html

[Zoodles]

Firstly, Victron does not seem to respond to technical support questions by us mere mortals...

I am interested in the comment above that LFP should not be directly paralleled with SLA... the idea is that it would be for a short term (2 mins?), urgent situation... but if this creates a problem I would like to know about it...

Also, the Argofet would not be in a charging (forward-biased) state, as the alternator would not be providing voltage yet (Regulator programmed for delay in ramping up after starting)... so, question is: are the output fet's vulnerable?

But I am interested in the comment of negative impacts of paralleling the LFP's with SLA's too...

[donradcliffe]

The LFP house battery and the AGM chassis batteries are combined while the engine alternator is putting out more than 13.5 volts in my RV. The combiner is a 200 amp voltage sensitive mechanical relay from Yandina, and I can force the relay on or off with a rocker switch to charge the AGM from the LFP/solar or to prevent overcharging the LFP (the alternator has a dumb 14.1 output).

The system has worked for over 2 years and 20,000 miles (5-700 engine hours).

[PaulCrawhorn]

There is nothing wrong with briefly paralleling LFP and lead banks for occasional jump starting

so long as you know what you're doing.

Issues include higher current than circuitry is designed for

inrush current at join time if V delta is over say half a volt

starter pulling too high amps

wiring infrastructure not robust enough

etc etc

maybe a high amp A/B switch rather than Both?

The House bank likely can crank fine in its own

[goboatingnow]

Paralleling a lithium with a low SOC to a LA with a high SOC is not a good idea as considerable balancing currents could flow albeit for a short time. This would reverse bias the lithium argofet

[donradcliffe]

I forgot to mention that Yandina recommends a minimum length of relatively high gauge wire between the two battery types to act as a current limiting resistor. I have measured the current in the crossover wire when the house bank is deeply discharged, and I saw 70 amps from a 180 amp alternator, which was fine with me and shouldn't stress anything. I am of the battery charging school that says a little patience is better than running all the gear to its advertised limits.

[rgleason]

In a hybrid LFP/SLA system, would it be better to use an adjustible Victron Smart DC-DC converter to
1. Keep the starter battery charged from the LFP.
2. Provide an inherent discharge path through the DC-DC charger to the FLA for any LFP BMS disconnect, to protect the alternator and system ele tronics?

Alt is charging LFP with wakespeed ws500 equivalent with current sensing and alt temp sensor using LFP settings.

[Catapault]

Originally Posted by rgleason

In a hybrid LFP/SLA system, would it be better to use an adjustible Victron Smart DC-DC converter to
1. Keep the starter battery charged from the LFP.
2. Provide an inherent discharge path through the DC-DC charger to the FLA for any LFP BMS disconnect, to protect the alternator and system ele tronics?

Alt is charging LFP with wakespeed ws500 equivalent with current sensing and alt temp sensor using LFP settings.

I prefer the reverse setup.

Charge the starter bat direct from the Alternator, keep the Engine system seperate from the House bank. I like independant systems.

Use a DC-DC from the Alternator to the lithium system. (And this may not even be needed, depending how you manage this charging source).

This has the side effect of protecting the Alternator as it always has a LA battery to dump into (the starter).

Of course you CAN replace alternators with more expensive ones, and other things like the Wakespeed, but I prefer not to. It really depends if this is a primary charge source for house bank, or a backup. In my case, it is a backup only.

[goboatingnow]

Most efficient is the alternator to the LFP bank as this is the bank requiring most charging . A small dc dc charger can be used to keep the starter toped up.

You can add a balmar alternator protector but your wakespeed has full remote disconnect ability.

[rgleason]

@goboatingnow Agreed. I understood from another thread that the victron smart dc-dc from lfp to charge sla starter battery will provide alternator protection in case the wakespeed does not shutdown and the lfp bms disconnects.
Also a Balmar APM would be another good backup.

The reason I ask these questions, is it appears that given these devices work as I think they do. it might be feasible to use drop-in lfp wirh bms with no external signal and relay/mosfet.

What do you think?