Two Chargers Simultaneous Charging

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coulomb
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Two Chargers Simultaneous Charging

Post by coulomb »

Paul9 wrote: No, not this time! This time the combined charge got up to 27.4amps and stayed there?
Paul, is it possible that last time you checked and the lead acid charger backed off quickly, you were using thinner cable temporarily, and now that it's wired in more permanently, the cables are thicker? The lead acid charger might have been getting a significant voltage drop across the charger cables, but now less drop?

Chargers really should have four output cables: two thick ones to deliver the power, and two much thinner wires to accurately sense the battery voltage, without being affecI'mted by the voltage drops. This is often referred to as a Kelvin connection. Perhaps one sense wire would do, assuming that the voltage drop across both cables would be the same. Though in many EVs, this may not be the case.

Edit: a quick note on how this would work. Suppose you have a battery that rests at 100 V, and is full at 110 V. With thin cables from the charger to the battery, at 25 A the battery might rise to sat 102 V due to its internal resistance, but the charger output might be say 108 V. The extra 6 V are dropped across the thin charger cables. So the charger thinks the battery is getting close to full, so it cuts back the charge current. With thicker cables, the voltage at the charger might rise to only 104 V (one third the voltage drop), so the charger continues at full current.
Last edited by coulomb on Sun, 17 Apr 2016, 08:57, edited 1 time in total.
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Paul9
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Two Chargers Simultaneous Charging

Post by Paul9 »

Thanks guys,

Thanks Peter C, I know what you are saying and I will bounce it off my electrician brother who is now also rather curious about what could be giving these conflicting results.

Thanks coulomb, as a matter of fact this time I used the exact same "Y" shaped cable (that I mentioned earlier in this thread) as I used in the two tests! As I mentioned, during the two tests, the base of the "Y" cable became warm so I reduced its length from 18 inches down to about 4 inches to reduce resistance and therefore heat build up. Knowing my cable connecting skills were not terrific, I went and bought another "Y" cable from Jaycar and took both the shortened cable and the new "unshortened" cable to my brother's place. He was keener about using the "unshortened" cable so we used it - exactly the same cable I had used in the tests.

No other cables have been touched!

Thanks
Paul
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Adverse Effects
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Two Chargers Simultaneous Charging

Post by Adverse Effects »

i asked because it sounded like the cases where not connected and now they are

a good test could be unbolting the old charger where it is and just sit it on a wood board and see if the same thing happens

i have seen a similar thing happen in duel PSU's in computer systems (dont know why it happens i am no EE)
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Two Chargers Simultaneous Charging

Post by Peter C in Canberra »

Adverse Effects wrote: ...have seen a similar thing happen in duel PSU's...


Maybe because the PSUs duel rather than dual! Image
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Two Chargers Simultaneous Charging

Post by Adverse Effects »

Peter C in Canberra wrote:
Adverse Effects wrote: ...have seen a similar thing happen in duel PSU's...


Maybe because the PSUs duel rather than dual! Image


Image
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Two Chargers Simultaneous Charging

Post by Paul9 »

Hi people,

I thought I would update this thread.

My brother and I fitted the old lead acid charger after having replaced the circuit breaker from a 10amp to 16amp. We then tried the stock-standard Jaycar "Y" cable and the two chargers started off at a combined 27.4 amps and the lead acid charger quickly dropped to 4 amps giving a total charge of 21.4 amps. Charging progressed smoothly until the BMS turned them both off as they were both attached through the same cable.

My brother was slightly concerned about heat build up in the base part of the "Y" cable where the full charge slightly exceeds the 10amp (240 volt) rating. We cut up a 15amp extension chord and used a junction box to connect the two 10amp cables to the 15amp cable.

I have charged up a few times and everything seems to be going well.

Thanks for every ones' advice!
Cheers
Paul
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