G'day I'm Cahn and in this video I wanted to test and demonstrate the difference between a VSR (AKA Smart Battery Isolator) compared to a DCDC when using either an AGM or a LiFePO4 aux battery... So I set up a simulated vehicle charging system on the bench complete with variable voltage power supply, starter battery, the DCDC and Voltage Sensitive Relay / Dual Battery Isolator and then of course a shunt to measure and display what was happening... then tested all the combinations: • AGM + VSR • AGM + DCDC charger • LiFePO4 + VSR • LiFePO4 + DCDC charger The idea is to actually see what happens to charging current, voltage, voltage drop and battery behaviour rather than just talking about the theory. I'll also show why a VSR can work perfectly well with some lead acid setups, but becomes a very different proposition once you introduce lithium. And rather than just telling you which one is "better", we'll put them both on the bench and see what actually happens. As always, thanks for watching and thanks to everyone who supports the channel! Keen to hear what setup you're running and how it's working for you! Cheers, Cahn
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One thing not taken into account in this testing setup, is fuel economy. I started my van life with a VSR + AGM setup. Everything was fine, and I was averaging 300kms per tank in my 2007 Mitsubishi Express Van After a year, I upgraded the battery to a lithium battery, while staying with a VSR. While the Lithium charged fine, and I had no issues. What I did notice, was my fuel economy. I dropped down to barely reaching 200kms per tank. TBH, because at that time, I wasn't that knowledgeable on VSR's I actually thought I had a fuel leak. I spent hundreds on Mechanics only for them to tell me they were adamant there was no leak. Eventually I saw a youtube vid on a Victron DCDC charger. It explained how bad VSR's are for lithium (still nothing about the fuel economy though.) So wanting to save my lithium and alternator from further harm, I quickly replaced my VSR with a 30amp Victron DCDC charger. Only then, did I find my fuel economy actually return to normal before the Lithium upgrade. Infact, I was getting a slightly better fuel economy, 330kms per tank. I could have saved hundreds... 😭😭😭
Another point to mention with VSRs, especially Redarc, is the ability to manually override them with a push button to link the batteries together for a self jump start in the event that the main batteries are flat
Would not suit everyone but I manually switch the DC-DC charger on when I chose to have it charge the lithium. Lots of solar on the roof so I rarely need to rely on the vehicle alternator/battery. Worth mentioning that with the DC-DC, the charging profile can be set to lead acid or lithium for a proper full charge. Not so with a VSR.
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well explained video. thank you.
For the ppl that aren't aware when installed in a vehicle most alternators only give about 25% or so rated current at idle rpm. So a 100 amp alt. at idle will only deliver about 25 amps. Most alternators don't deliver rated or close to rated output until about 2,000+ rpm.
I run a 12v relay that coupled to my Ranger overhead switches. So it's only powered when car is on, and can also manually turn it on/off.
You seem to have some electrical or electronic background, like me. I find it challenging to explain 12V systems to off-roaders with no training in the field, especially when Ohm's Law comes into play with wiring sizes and length, and charging and solar sytem design. I have been following your journey and I have to say, you offer the clearest explanations of some complex concepts on YT that I have seen. Well done Cahn! For the past 5 years I've personally used a Victron Solid State Isolator, connected directly to my alternator, for my Calcium starter battery and my LiFePo accessory battery in my 4WD. Once you get the ignition wire connection sorted, it works.
Excellent demonstration! I have been talking to boat owners about this for more than 15 years so it's a no-brainer for me. I usually say that it's not a Battery Isolator, I call it a battery coupler, and nothing will be better than the worst battery (They are never equal!). I noticed that about :50 the current dropped fairly quick, despite that the voltage was constant. This due to the voltage in the aux battery is rising during charging. A DCDC compensate for this and can keep a constant charging current until the voltage reahes 14.8 V, when the DCDC changes from bulk mode to absorption mode. With a DCDC the aux battery is always charged faster and to a higher level, 100% instead of appr 85%.
I'd install a DCDC charger, as I intend to use a power station and like to charge it while driving.
Very useful content Thankyou.
the big problem with VSR's is modern cars with smart alternators, after 10 or 15 min of driving they sense the start battery is charged and turn down the amps
Can you use a VSR and a DCDC charger together?
Nice video, Cahn. I was charging house AGM and vehicle starter batteries via a relay in our motorhome and found that, after buying new starter batteries (2 x 12V 990CCA), joining the batteries caused problems with the engine thanks to the voltage/current issues playing havoc with the various computers - even on my '96 6.5L V8 diesel. A DC-DC charger fixed that. It also means I can switch to lithium house batteries later without spending more money.
Great video. However you'd need one more scenario, with hybrid SUV especially the PHEVs becoming more popular. With my hybrid 2016 Rav4 I would limit the LFP charging draw when vehicle is PWR-ON to 8 amps. Either with a charge controller or on a digital DC-to-DC converter. To not overtax the existing electronics (Toyota's DC-to-DC from it's HV battery). Apparently they are very expensive to repair, someone using a DC-to-AC inverter pulling over 1000w continuous burnt it out and thus an expensive repair. I imagine the Outlander PHEV is similar in this regard.
Great video A suggestion on the benefits of a vsr under the hood Connect to a dc dc charger in the caravan next to the lithium battery
Hi Cahn in a future video it would be interesting to see a comparison of resistance/heat at different currents between blade, maxi, midi, mrbf and mega fuses and circuit breakers
Nice work Cahn
I think I would put the voltage sensing circuit of a VSR on a relay connected to 'switched on', this would cut the connection to the second battery without ignition and save juice in the second battery if the was a drain.
Great video